effects of elevated co2 and agricultural management on ......integration technique (i.e.,...

Brye and Gbur

Jones M 1 1973 The organic matter content of savanna soils of West Africa 1 Soil Sci 2442-53

Maxwell G R D G Binkley and D G West 1972 Soil Survey of Arkansas County Arkansas United States Department of Agriculture Soil Conservation Service Washington DC

National Oceanic and Atmospheric Administration (NOAA) 2002 Climashytography of the United States No 81 Monthly Station Normals of Temperature Precipitation and Heating and Cooling Degree Days 1971-2000 Arkansas United States Department of Commerce National Climatic Data Center Asheville NC

Parton W 1 D S Schimel C V Cole and D S Ojima 1987 Analysis of factors controlling soil organic matter levels in Great Plains grasslands Soil Sci Soc Am 1 51 1173-1179

Phillips W W and M D Harper 1977 Soil Survey of Benton County Arkansas U S Department of Agriculture Soil Conservation Service Washington DC

348 I wwwsoilscLcom

Soil Science bull Volume 175 Number 7 July 2010

Slaton N A (ed) 2001 Rice Production Handbook University of Arkansas Cooperative Extension Service MP192 126 p

Steller R M N A Jelinski and C 1 Kucharik 2008 Developing models to predict soil bulk density in southern Wisconsin using soil chemical properties 1 [ntegr Biosci 453-63

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) 2006 Keys to Soil Taxonomy Tenth Edition [Online] Available from ftpftp-fcscegovusdagovINSSCI Soil_ Taxonomykeyskeyspdf (verified January 7 2010)

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Soil Survey Division (SSD) 2009 Soil Series Name Search [Online] Available from httporthoftwnrcsusda govcgi-binlosdosdnamequerycgi (verified July 10 2009)

United States Department of Agriculture (USDA) Soil Conservation Service (SCS) 1981 Land Resource Regions and Major Land Resource Areas of the United States Agriculture Handbook 296 Washington DC

copy 2010 Lippincott Williams amp Wilkins

TECHNICAL ARTICLE

bull

Effects of Elevated CO2 and Agricultural Management on Flux of Greenhouse Gases From Soil

Katy E Smithl G Brett Runion2 Stephen A Prior 2 Hugo H Rogers2 and H Allen Torbert2

Abstract To evaluate the contribution ofagriculture to climate change the flux of greenhouse gases from different cropping systems must be assessed Soil greenhouse gas flux (C02 N20 and CH4) was assessed during the final growing season in a long-term (1 a-year) study evaluatshying the effects of crop management (conservation and conventional) and atmospheric CO2 (ambient and twice ambient) on a Decatur silt loam (clayey kaolinitic thermic Rhodic Paleudults) Seasonal soil CO2

flux was significantly greater under elevated (439 Mg COrC ha-I) versus ambient CO2 (334 Mg CO2-C ha- I) and was generally greater in the conventional (419 Mg COrC ha-I) compared with the consershyvation (353 Mg COrC hamiddot l ) system Soil flux ofboth N20 (range -15 to 534 g N20-N ha-I day-I) and Cli (range -79 to 244 g Cli-C ha- I

day- I) were low throughout the study and rarely exhibited differences caused by treatments Global wanning potential (calculated based on flux of individual gases) was increased by elevated CO2 (334) and by conventional management (171 ) these increases were driven primarily by soil CO2 flux As atmospheric CO2 continues to rise our results suggest adoption of conservation management systems represents a viable means of reducing agricultures potential contribution to global climate change

Key words Carbon dioxide global change greenhouse gases methane nitrous oxide

(Soil Science 2010 175 349-356)

T he level of carbon dioxide (C02) in the atmosphere has inshycreased from approximately 280 ppm at the beginning ofthe

industrial revolution to approximately 380 ppm today primarily because of fossil fuel burning and land use change (Keeling and Whorf 2001) resulting in increased attention to the global carbon (C) cycle Approaches for mitigating the increase in atshymospheric CO2 are being proposed One such method is the storage of C in agricultural soils (Kern and Johnson 1993 McCarl and Schneider 200 I West and Post 2002) Research by our group and others (Amthor 1995 Torbert et aI 2000 Prior et aI 2005) has shown that soil C storage is generally increased under elevated atmospheric CO2 primarily because of increased biomass production Although increased storage of C can enshyhance soil quality the stability of this C as well as the impact of elevated CO2 and land management practices on the emisshysions of greenhouse gases (GHG) need to be addressed to fully understand the contribution of agriculture to climate change in the future

I

In addition to COz methane (CH4) and nitrous oxide (N20) are important GHG potentially contributing to global climate change Animal and crop production may account for as much

I IDepartment of Math Science and Technology University of Minnesota Crookston Crookston MN 56716 Dr Katy E Smith is correspondingI author E-mail katysumnedu 2USDA-ARS National Soil Dynamics Laboratory Auburn AL

I Received January 13 2010 Accepted for publication May 21 20 IO

I Copyrightcopy 2010 by Lippincott Williams amp Wilkins ISSN 0038-075XI DO[ 101097SS0b013e318Ie93d3c

I Soil Science bull Volume 175 Number 7 July 2010

~

as 70 ofannual global anthropogenic N20 emissions and about 33 of global CH4 emissions with these agricultural emissions projected to increase (Mosier et aI 1998 Mosier 2001) A more detailed accounting of natural and anthropogenic N20 and CH4

sinks and sources has recently been published (US EPA 2010) Given the potential of these GHG to contribute to global clishymate change impacts of management and environmental factors on their flux from soils have begun to be more intensively assessed Cultivation and application of fertilizer N have been shown to inhibit CH4 oxidation in soil (Mosier et aI 1991 1996 Kessavalou et aI 1998 Khalil and Baggs 2005) Kessavalou et al (1998) found that CH4 and N 20 flux from agricultural soils increased following tillage events and suggested that no-tillage systems represented a lower threat to deterioration of both atshymospheric and soil quality Li et al (2005) found that farmyard manure application increased C sequestration while increasshying N20 emissions with little impact on CH4 emissions For 20 years increased N20 emissions from this system offset C sequestration from 75 to 310 depending on the land manshyagement practice However Parkin and Kaspar (2006) found no differences in N20 emissions between different management systems in a com-soybean rotation Johnson et al (2007) conshycluded that agricultural practices such as reduced tillage will increase soil organic C and potentially enhance CH4 consumpshytion imparting a net positive impact on the emissions of GHG despite increased emissions ofN20 observed in no-till systems

In addition to land management practices elevated atmoshyspheric CO2 has been shown to increase emissions of GHG Elshyevated atmospheric CO2 generally increases soil CO2 flux in the range of 15 to 50 (Nakayama et aI 1994 Verburg et aI 1998 Zak et aI 2000) This increased soil CO2 flux can be caused by effects ofelevated CO2 on autotrophic (ie plants) (Nakayama et aI 1994 Vose et aI 1997 Zak et aI 2000) andor heteroshytrophic (ie soil microbes) (Nakayama et aI 1994 Vose et aI 1997 Zak et aI 2000) respiration

In addition to soil CO2 flux elevated atmospheric CO2 can impact CH4 and N20 flux Cheng et al (2006) reported a 58 increase in CH4 flux from rice paddies under elevated CO2 This increase was attributed to greater root exudates and numbers of tillers resulting in more surface area for the release of CH4 to the atmosphere (Ziska et aI 1998 Inubushi et aI 2003) Howshyever Chan and Parkin (200 Ib) reported that when exposed to elevated concentrations of atmospheric CH4 well-drained agrishycultural soils may become CH4 sinks Nitrous oxide flux was not affected by elevated CO2 in the rice study by Cheng et al (2006) However Kettunen et al (2006) showed that elevated CO2 inshycreased both N20 flux from soil and soil water content

These variable findings demonstrate that agriculture may act as a source or a sink for GHG under conditions of elevated CO2 This as well as their impact on global climate demonshystrates a need to evaluate GHG fluxes under different land use and soil management practices Furthermore many previous studies evaluating soil GHG flux have been conducted in shortshyterm field trials Therefore there is a need to measure GHG flux from long-term studies under different land management pracshytices and at different levels of atmospheric CO2 The objective

wwwsoilscicomI349

I I

I I

I

I


The experiment was conducted using a split-plot design with three replicate blocks Whole-plot treatments (management system) were randomly assigned to half of each block Split-plot treatments (C02 levels) were randomly assigned to one OTC each within each whole plot There were a total of 12 OTC with six of these being ambient CO2 (three for conventional manshyagement and three for conservation management) and the other six being elevated CO2 (three for conventional management and three for conservation management) Data (including GWP) were totaled across the growing season using a basic numerical integration technique (ie trapezoidal rule Leithold 1976) It is important to note that these calculations were made strictly for overall treatment comparisons and were not intended to generate quantitative numbers of soil GHG losses due to the relatively low sampling frequency (13 sampling dates across 178 days of study) Statistical data analyses were performed using the Mixed Procedure of the Statistical Analysis System (Littell et aI 1996) A significance level of P 005 was esshytablished a priori trends were considered at 005 gt P 2 010

RESULTS

CO2 Flux Elevated atmospheric CO2 (main effect across both manshy

agement systems) increased soil CO2 flux on five sampling dates (Table 1) similar trends were noted on four other dates Conshyventional management (main effect across both CO2 treatments) had significantly higher soil CO2 flux only on a single date two other dates showed similar trends (Table I) No significant inshyteraction of CO2 and management was observed

Soil CO2 flux from the conventional management system increased in both CO2 treatments following a tillage event (day of year [DaY] 138 Fig IA) this did not occur in the consershyvation system (Fig IB) After this increase soil CO2 flux was primarily affected by rainfall in all treatments increasing after rainfall events and decreasing as soil dried (Fig I C) Although soil water content followed rainfall patterns in all treatments it

CO2 and Management Effects on Soil Gas Flux

should be noted that the conservation system had a higher soil water content than did the conventional system (Fig lC) soil water content did not differ among the CO2 treatments (data not shown) Soil CO2 flux response to elevated CO2 was more freshyquent in the conventional management system (significant inshycreases on DaY 131 180 and 250 with similar trends on DaY 173 194 229 and 292) (Fig IA) than in the conservation system (significant increase on DaY 173 with similar trends on DaY 131 180 and 215) (Fig IB)

When totaled across the growing season soil CO2 flux was significantly higher under elevated (439 Mg COz-C ha -I) than ambient (334 Mg COz-C ha -I) atmospheric CO2 conditions Similarly the conventional system (419 Mg COz-C ha -I) had significantly higher seasonal soil CO2 flux than did the consershyvation system (353 Mg COz-C ha- I

)

N20 Flux There was no main effect of elevated CO2 on soil N20 flux

(Table 1) The main effect of management was that the conshyventional system had significantly higher soil N20 flux on three dates (Table I) As with CO2 flux there were no significant interactions between CO2 and management treatments

Soil N20 flux was low throughout most of the study period for all treatments (Fig 2) Although soil N20 flux increased in association with rain that occurred in late June to mid-July (DaY 180-194) in the conservation system under elevated CO2

(Fig 2B) this relatively small increase did not result in sigshynificant treatment effects caused by a large variability among samples

When totaled across the growing season there were no significant differences in soil N20 flux for the CO2 treatment (ambient 2914 g N20-N ha - elevated 8912 g N20-N ha -I)

Similarly management did not have a significant effect on soil N20 flux (conventional 4576 g N20-N ha -I conservation 7250 g N20-N ha -I) Although the interaction of CO2 and management on seasonal N20 flux was not significant it is inshyteresting to note that flux in the conservation system was about

TABLE 1 Statistic~ for CO2 Concentration Management System (M) and Their Interaction (C x M) on Soil CO2 N20 and CH4 Flux for the Sampling Dates in 2007

Variable t

CO2 N20 CH4

DOY CO2 M C x M CO2 M CxM CO2 M CxM

115 0460 0932 0653 0925 0718 0682 0019 0183 0141 131 0010 0101 0324 0404 0237 0218 0802 0417 0630 153 0666 lt0001 0204 0411 0014 0135 0720 0642 0904 173 0016 0093 0816 0221 0477 0616 0960 0934 0419 180 0006 0110 0203 0346 0198 0094 0030 0325 0648 187 0093 0655 0645 0362 0340 0387 0102 0306 0833 194 0057 0146 0593 0358 0348 0330 0955 0725 0361 215 0171 0662 0226 0597 0400 0559 0523 0236 0407 229 0062 0087 0296 0383 0048 0694 0435 0329 0359 250 0007 0250 0064 0216 0395 0108 0219 0381 0853 264 0079 0362 0750 0638 0014 0269 0493 0016 0044 278 0682 0668 0242 0643 0433 0967 0518 0085 0457 292 0049 0309 0744 0577 0432 0210 0993 0509 0340 Total 0002 0043 0127 0281 0617 0389 0946 0224 0174

Prgt F statistics Bold represents significance tOOY day of year CO2 carbon dioxide in kg COrC ha -[ day -I N20 nitrous oxide in g N20-N ha -[ day -I C~ methane in g C~-C ha -Iday -I

copy 2010 Lippincott Williams amp Wilkins wwwsoilscicom I 351

Soil Science bull Volume 175 Number 7 July 2010Smith et al

of the current study was to evaluate the flux of GHG (C02

N20 and CH4) from conventional and conservation manageshyment systems that had been under the influence of elevated atshymospheric CO2 for 10 years

MATERIALS AND METHODS The experiment was conducted at the outdoor soil bin fashy

cility located at the USDA-ARS National Soil Dynamics Labshyoratory in Auburn AL (326degN 85YW) in a bin (7 x 76 x 2 m deep) filled with a Decatur silt loam soil (clayey kaolinitic thermic Rhodic Paleudults) The soil bin facility was constructed in the mid-1930s and the soil bins have since been primarily used for the development and testing of new agricultural mashychinery thus they were kept mechanically fallow throughout most of their history The uniformity of these bins provide for a much more homogeneous soil leading to more consistent plant growth patterns than found in a typical field setting

Crops within the soil bin were grown from seed to matushyrity in open-top chambers (OTC) (Rogers et aI 1983) under ambient and elevated atmospheric CO2 levels in two different crop management systems (conventional and conservation) Carbon dioxide was supplied from a 127 Mg liquid CO2 reshyceiver through a high-volume dispensing manifold Atmospheric CO2 concentration was elevated by continuous injection of CO2

into plenum boxes as detailed in Mitchell et a1 (1995) Carbon dioxide concentrations were continually monitored (24 h day -I) using a time-shared manifold with samples drawn through soshylenoids to an infrared CO2 analyzer (Model 6252 LI-COR Inc Lincoln NE) The mean daytime CO2 concentrations were 37539 plusmn 007 j-LLL -I (SE) (n = 109562 ambient CO2 treatshyment) and 68327 plusmn 023 j-LLL -I (SE) (n = 109591 elevated CO2 treatment) The target concentration for the elevated CO2

treatment was 720 j-LLL -I The only downtime for CO2 exposhysure was associated with tillage and planting operations as deshyscribed later

This report reviews soil-atmosphere GHG flux (Cal CH4

N20) in the final growing season of a lO-year elevated CO2

study (1997-2007) comparing two crop management systems (conventional and conservation) These crop management and crop rotation sequences have been previously described in detail (Prior et aI 2005 2010) Briefly the conventional system used a grain sorghum [Sorghum bicolor (L) Moench Pioneer 8282] and soybean [Glycine max (L) Merr Asgrow 6101] rotation with spring tillage and winter fallow To simulate spring tillage operations in this system the following procedures were used (i) a pitchfork was inserted (10 cm between insertion points) to a depth of 20 to 25 cm before heaving the soil to simulate a chisel plow operation (ii) a large push-type PTa tiller (Model 192432 Gardenway Inc Troy NY) was operated twice to a soil depth of 15 to 20 cm to simulate two disking operations and (iii) a small push-type garden cultivator (Model 41OR Ryobi Technolgies Inc Anderson SC) was operated to a soil depth of 8 to 10 cm to simulate a field cultivation operation In the conservation system grain sorghum and soybean were also rotated with three cover crops in the order of crimson clover (Trifolium incarnatum L AU Robin) sorghum sunn hemp (Crotalaria juncea L Tropic Sunn) wheat (Triticum aestivum L Pioneer 2684) and soybean The conservation system used no-tillage pracshytices with no fallow periods In both management systems row crop seeds were sown (201m of row) on 038-m row spacings using a hand-operated precision garden seeder (Model 1001-B Earthway Bristol IN) To ensure adequate plant establishment and grain production for sorghum and wheat fertilizer N (amshymonium nitrate) was broadcast applied in split applications For

350 I wwwsoilscicom

grain sorghum fertilizer N was applied at a rate of 34 kg N ha -I shortly after planting and an additional 10 1 kg N ha -I was applied 30 days after planting For wheat fertilizer N was apshyplied at planting (34 kg N ha -I) 35 months after planting

I(674 kg N ha -I) and 45 months after planting (34 kg N ha- ) Because clover soybean and sunn hemp are nitrogen fixers they received no fertilizer N however seeds were inoculated with commercial Rhizobium (Nitragin Co Milwaukee WI) beshyfore planting Cover crops and sorghum were terminated with glyphosate (N-[phosphonomethyl] glycine) 10 days before plantshying the following crop to prevent regrowth All operations previshyously described were also conducted on all nonexperimental areas to ensure uniform treatment of areas bordering the study plots Rainfall was measured on-site throughout the study period

Soil flux measurements were taken in the final soybean crop using custom-made trace gas flux chambers constructed acshycording to the GRACEnet (Greenhouse gas Reduction through Agricultural Carbon Enhancement Network) chamber-based trace gas flux measurement protocol (Parkin and Kaspar 2006) Two polyvinylchloride rings (254-cm diameter x 1O2-cm tall) were installed between rows in each plot to a depth of approxishymately 51 cm These rings served as bases for flux chambers and were left in place throughout the experiment unless they needed to be removed for tillage and planting Midday flux measurements were conducted approximately every other week by sealing vented chambers (254-cm diameter x 114-cm tall) onto the rings before collecting gas samples at 0 15 30 and 45 min after chamber closure Chambers are constructed from polyvinylchloride and covered with reflective tape At each time point for sampling gas samples (l0 mL) were collected with polypropylene syringes and immediately injected into evacushyated glass vials (6 mL) fitted with butyl rubber stoppers as described by Parkin and Kaspar (2006) The overpressure fashycilitates subsequent removal of the gas sample for analysis Samples were then injected into a Shimadzu GC-2014 gas chromatograph (Shimadzu Scientific Instruments Inc Columshybia MD) containing three detectors a thermal conductivity deshytector for CO2 analysis an electrical conductivity detector for N20 analysis and a flame ionization detector for CH4 analysis Gas levels were determined by comparison with triplicate runs of standard gases of known concentration (Scott Specialty Gases Plumsteadville PA) and flux rates were then computed from the change in gas concentration over time It is important to note that all trace gas collection and processing procedures previously deshyscribed were conducted according to GRACEnet measurement protocols (Parkin and Kaspar 2006)

Soil water content (m3 m -3) was measured periodically throughout the course of this experiment using time-domain reflectometry using a Tektronix 1502B cable tester (Tektronix Inc Beaverton OR) The soil moisture sensors had 20-cm-Iong stainless steel rods with a rod spacing of 30 cm The sensors were installed vertically from the soil surface for a reading depth of 0 to 20 cm Sensors were placed between rows positioned close to the gas sampling collars Measurements were converted to volumetric water content values using Topps equation (Topp et aI 1980)

Each GHG has an established Global Warming Potential (GWP) defined as the ratio of radiative forcing from 1 kg of a gas to 1 kg of CO2 over a specific interval of time The GWP of CO2 is 1 whereas the GWP of CH4 is 25 and that of N20 is 298 (Forster et aI 2007) In our study we multishyplied the cumulative flux of each gas across the growing seashyson by its appropriate defined ratio these values were totaled to give seasonal GWP for each individual plot across all treatshyment combinations


1

Smith et al











350 I wwwsoilscicom


grain sorghum fertilizer N was applied at a rate of 34 kg N ha -I shortly after planting and an additional 10 1 kg N ha -I was applied 30 days after planting For wheat fertilizer N was apshyplied at planting (34 kg N ha -I) 35 months after planting (674 kg N ha -I) and 45 months after planting (34 kg N ha- I

) Because clover soybean and sunn hemp are nitrogen fixers they received no fertilizer N however seeds were inoculated with commercial Rhizobium (Nitragin Co Milwaukee WI) beshyfore planting Cover crops and sorghum were terminated with glyphosate (N-[phosphonomethyl] glycine) 10 days before plantshying the following crop to prevent regrowth All operations previshyously described were also conducted on all nonexperimental areas to ensure uniform treatment of areas bordering the study plots Rainfall was measured on-site throughout the study period





Soil Science bull Volume 175 Number 7 July 2010 CO2 and Management Effects on Soil Gas Flux


RESULTS





When totaled across the growing season soil CO2 flux was significantly higher under elevated (439 Mg COz-C ha -I) than ambient (334 Mg COz-C ha-I) atmospheric CO2 conditions Similarly the conventional system (419 Mg COz-C ha-I) had significantly higher seasonal soil CO2 flux than did the consershyvation system (353 Mg COz-C ha- I

)

N2 0 Flux There was no main effect of elevated CO2 on soil N20 flux




When totaled across the growing season there were no significant differences in soil N20 flux for the CO2 treatment (ambient 2914 g N20-N ha- elevated 8912 g N20-N ha -I)

Similarly management did not have a significant effect on soil N20 flux (conventional 4576 g N20-N ha -I conservation 7250 g N20-N ha-I) Although the interaction of CO2 and management on seasonal N20 flux was not significant it is inshyteresting to note that flux in the conservation system was about


Variable t

CO2 N20 CH4


115 0460 0932 0653 0925 0718 0682 0019 0183 0141 131 0010 0101 0324 0404 0237 0218 0802 0417 0630 153 0666 lt0001 0204 0411 0014 0135 0720 0642 0904 173 0016 0093 0816 0221 0477 0616 0960 0934 0419 180 0006 0110 0203 0346 0198 0094 0030 0325 0648 187 0093 0655 0645 0362 0340 0387 0102 0306 0833 194 0057 0146 0593 0358 0348 0330 0955 0725 0361 215 0171 0662 0226 0597 0400 0559 0523 0236 0407 229 0062 0087 0296 0383 0048 0694 0435 0329 0359

I 250 264

0007 0079

0250 0362

0064 0750

0216 0638

0395 0014

0108 0269

0219 0493

0381 0016

0853 0044

I 278 0682 0668 0242 0643 0433 0967 0518 0085 0457

I 292 Total

0049 0002

0309 0043

0744 0127

0577 0281

0432 0617

0210 0389

0993 0946

0509 0224

0340 0174

I Prgt F statistics Bold represents significance tOOY day ofyear CO2 carbon dioxide in kg COrC ha-[ day -I N20 nitrous oxide in g N20-N ha-[ day -I C~ methane in g C~-C ha-Iday -I

I

1 I


I I

I I

I I


40

30

20 co J

y i 10 ()

CI

0

A -10

40

30

c 20 co J ()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02 1 3 u ~ 01

E l

~

--Elevated Conventional Tillage --ltgt-- Ambient

--Elevated Conservation Tillage ~Ambient

_Rainfall

--+--- Conventional

--tr- Conservation

100 125 150 175 200 225 250 275 300

c Day of Year

120

100

80 E sect

60 c

OJ 40 c

20

FIG 3 Flux of CH4 from a conventional management system (A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil CH4 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period

When totaled across the growing season there were no significant differences in soil CH4 flux for the CO2 treatment (ambient 950 g CH4-C ha- J elevated 883 g CH4-C ha- 1)

Similarly management did not have a significant effect on soil CH4 flux (conventional 1928 g CH4-C ha -1 conservation -95 g CH4-C ha -1)

Global Warming Potential Given that soil N20 and CH4 flux were both low throughshy

out the study GWP was dominated by soil CO2 flux In fact the contribution of soil CO2 flux to GWP was between 97 and 99 for each of the treatment combinations (data not shown) When totaled across the growing season GWP was



significantly higher (P = 0002) under elevated (164907 CO2 equivalents ha -1) than ambient (123584 CO2 equivalents ha - J) atmospheric CO2 conditions Similarly the conventional sysshytem (155633 CO2 equivalents ha- J) tended to have a higher (P = 0094) seasonal GWP than did the conservation system (132858 CO2 equivalents ha- 1

) There was no significant inshyteraction (P = 0225) between CO2 and management treatments

DISCUSSION

CO2 Flux Elevated atmospheric CO2 in our study increased soil CO2

flux on several dates and for the seasonal total with the increase being in the range of 15 to 50 as reported in the literature (Nakayama et aI 1994 Verburg et aI 1998 Zak et aI 2000) Elevated CO2 can increase soil CO2 flux in several ways First elevated CO2 increases plant growth with roots often showing the greatest relative increase among plant organs (Rogers et aI 1994) Greater root biomass can lead to increased autotrophic respiration (Nakayama et aI 1994 Zak et aI 2000) Second roots of plants grown under elevated CO2 show increased root exudation (Norby et aI 1987 Lekkerkerk et aI 1990) leading to larger pools of labile C in the rhizosphere (Zak et aI 1993) This increase in easily decomposable C can increase heteroshytrophic respiration by increasing the size and activity of rhizoshysphere microbial communities (Goudriaan and de Ruiter 1983) Third elevated CO2 can increase heterotrophic respiration via increasing the amount of plant residue on the soil available for microbial decomposition (Torbert et aI 2000) Lastly elevated CO2 has been shown to increase plant water use efficiency (Rogers and Dahlman 1993 Prior et aI 2010) This in comshybination with greater surface residue (Prior et aI 2005) reducing evaporative water losses (Reicosky et aI 1999) could increase microbial activity and lead to increased heterotrophic respirashytion Therefore the increased soil CO2 flux noted here was not unexpected However the increase in soil C observed in this study resulting from increased biomass production (Prior et aI 2005 Runion et aI 2009) indicates that the elevated CO2 treatments are storing soil C despite higher soil CO2 flux

In contrast to atmospheric CO2 treatments management had little effect on soil CO2 flux A major exception was the large increase in soil CO2 flux after tillage in the conventional system This has been observed by others and is caused by the immediate release of CO2 from mechanical (physical) soil disturbance (Prior et aI 1997 2000 2004 Reicosky 1997 Franzluebbers et aI 1998 Morris et aI 2004) Because tillage results in mixing of soil with surface residue the C substrates are rapidly acted upon by microbes (biological) resulting in furshyther flux of CO2 to the atmosphere (Franzluebbers et aI 1998 Morris et aI 2004 Prior et aI 2004 Runion et aI 2004) Despite the added biomass from cover crops in the conservation system (and its potential benefit in conserving soil moisture) soil CO2 flux was not significantly different from that measured in the conventional system on most dates In fact the conservashytion system had a 16 reduction in soil CO2 flux when totaled across the entire season most likely resulting from the large loss occurring in the conventional treatment during tillage This lower CO2 loss in conjunction with residue from both row and cover crops not being incorporated in the conservation system resulted in a significant increase in soil C storage in this system (Prior et aI 2005 Runion et aI 2009)

Our observed increase in soil CO2 flux following rainfall in both management systems has been reported in many ecosysshytems (Birch 1958 Davidson et aI 1993 Reicosky et aI 1999 Franzluebbers et aI 2000 Borken et aI 2003 Austin et aI

wwwsoilscicomI353

Smith et al Soil Science bull Volume 175 Number 7 July 2010

70000 __ Elevated Conventional Tillage ~Ambient60000

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0

70000 __ Elevated Conservation Tillage

60000 ~Ambient

50000 c

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

12004 _Rainfall

ME --- Conventional 100

1 03 C 80 Ec sect0 () 60 ll

02 ~

c co OJ

40 c3 u Oi E l (5 gt

C FIG 1 Flux of CO2 from a conventional management system (A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil CO2 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period

half that in the conventional system under ambient CO2 condishytions (3927 g N20-Nha-1 day -1 and 1989 g N20-Nha-1 day-l for conventional and conservation respectively) whereas the opshyposite occurred under elevated CO2 (5224 g N20-N ha-1 day-l and 12600 g N20-N ha- 1 day-J for conventional and consershyvation respectively)

CH4 Flux Elevated atmospheric CO2 decreased soil CH4 flux on two

sampling dates (Table 1) Conventional management had sigshynificantly higher soil CH4 flux on one date one other date showed a similar trend (Table 1) A significant interaction ofCO2

and management was observed on DOY 264 in which conshy

352 I wwwsoilscicom

01

20

125 150 175 200 225 250 275

Day of Year

ventional management had significantly higher soil CH4 flux only in the elevated CO2 treatment

As with N20 soil CH4 flux tended to be low throughout the study (Fig 3) In general soil CH4 flux tended to be less reshysponsive to rainfall than did the other trace gases although CH4

flux did tend to decrease during drier periods An exception to this was noted where CH4 flux increased after rain late in the growing season on DOY 264 as the treatment interaction preshyviously detailed It was noted that soil CH4 flux was sometimes negative this occurred in all treatment combinations with similar frequency (five or six sampling dates) and treatment differences were rarely significant (as noted for the previously mentioned main effects)

70 ____ Elevated Conventional Tillage

60 ~Ambient

50 C

co 40

J 30Z

~ 20Z CI

10

0

A -10

70

60

50

40

co J

30Z 6 Z 20

CI 10

0

B -10

__ Elevated Conservation Tillage --ltgt-- Ambient

04 120

1 _Rainfall

--+--- Conventional 100E - 03 c

80 Ell c sect0

60 ll c 02

cco OJ3 40 c u 01Oi

20E l (5 gt 0

100 125 150 175 200 225 250 275 300 0

C Day of Year

FIG 2 Flux of N2 0 from a conventional management system (A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil N2 0 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period


J~

Smith et al

70000 __ Elevated Conventional Tillage

60000 ~Ambient

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

c 50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

04 120

ME _Rainfall

--- Conventional 100

1 03 C 80 E c sect 0 ()

02 60 ~

ll c co OJ 3 40 c u 01 Oi E 20 l (5 gt

125 150 175 200 225 250 275

C Day of Year

FIG 1 Flux of CO2 from a conventional management system (A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil CO2 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period

half that in the conventional system under ambient CO2 condishytions (3927 g N20-Nha -1 day -1 and 1989 g N20-Nha -1 day-l for conventional and conservation respectively) whereas the opshyposite occurred under elevated CO2 (5224 g N20-N ha -1 day-l and 12600 g N20-N ha- 1 day-J for conventional and consershyvation respectively)


sampling dates (Table 1) Conventional management had sigshynificantly higher soil CH4 flux on one date one other date showed a similar trend (Table 1) A significant interaction of CO2

and management was observed on DOY 264 in which con-

352 I wwwsoilscicom






60 ~Ambient

50 C

40 co

J

Z 30

~ 20 Z CI

10

0

A -10


60 --ltgt-- Ambient

50

40

co J

30 Z 6

20 Z CI

10

0

B -10

04 120

1 _Rainfall

E --+--- Conventional 100

- 03 c

80 E ll c sect 0 c 02 60 ll c co OJ 3 40 c u 01 Oi E 20 l (5 gt 0 0

100 125 150 175 200 225 250 275 300

C Day of Year

FIG 2 Flux of N20 from a conventional management system (A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil N20 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period


--tr- Conservation

80

60

40

20


100 125 150 175 200 225 250 275 300

c Day of Year



DISCUSSION



In contrast to atmospheric CO2 treatments management had little effect on soil CO2 flux A major exception was the large increase in soil CO2 flux after tillage in the conventional system This has been observed by others and is caused by the immediate release of CO2 from mechanical (physical) soil disturbance (Prior et aI 1997 2000 2004 Reicosky 1997 Franzluebbers et aI 1998 Morris et aI 2004) Because tillage results in mixing ofsoil with surface residue the C substrates are rapidly acted upon by microbes (biological) resulting in furshyther flux of CO2 to the atmosphere (Franzluebbers et aI 1998 Morris et aI 2004 Prior et aI 2004 Runion et aI 2004) Despite the added biomass from cover crops in the conservation system (and its potential benefit in conserving soil moisture) soil CO2 flux was not significantly different from that measured in the conventional system on most dates In fact the conservashytion system had a 16 reduction in soil CO2 flux when totaled across the entire season most likely resulting from the large loss occurring in the conventional treatment during tillage This lower CO2 loss in conjunction with residue from both row and cover crops not being incorporated in the conservation system resulted in a significant increase in soil C storage in this system (Prior et aI 2005 Runion et aI 2009)


wwwsoilscicomI353

40

30

20co

J

y i 10 ()

CI

0

A -10

40

30

c co 20 J

()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02

1 3 u ~ 01

E l

~

FIG 3



_Rainfall

--+--- Conventional

Flux of CH4 from a conventional management system

120

100

E sect

c

OJc

(A) and a conservation management system (B) exposed to elevated and ambient levels of atmospheric CO2 for 10 years Soil CH4 flux data were collected during the final growing season in this study The arrow indicates when tillage occurred (conventional system only) Asterisks represent dates when the CO2 treatments differed significantly (PO 005 005 lt PO 01 0) Rainfall (solid bars) and volumetric soil water content (C) are shown for this same sampling period


Similarly management did not have a significant effect on soil CH4 flux (conventional 1928 g CH4-C ha -1 conservation

I -95 g CH4-C ha -1)

I Global Warming Potential Given that soil N20 and CH4 flux were both low throughshyI out the study GWP was dominated by soil CO2 flux In fact

the contribution of soil CO2 flux to GWP was between 97 I and 99 for each of the treatment combinations (data not

I shown) When totaled across the growing season GWP was

I copy 2010 Lippincott Williams amp Wilkins

J~


become an increasingly important issue because of its impact on fluxes of GHG and these effects may become more proshynounced as atmospheric CO2 continues to rise Our results inshydicate that conversion to conservation management may reduce agricultures potential contribution to global climate change

ACKNOWLEDGMENTS The authors thank B G Dorman J W Carrington and

HM Finegan for technical assistance This publication is based on work supported by the Agricultural Research Service under the ARS GRACEnet Project and by the Biological and Envishyronmental Research Program Us Department of Energy Inshyteragency Agreement No DE-AI02-95ER62088

REFERENCES

Amthor J S 1995 Terrestrial higher-plant response to increasing atmoshyspheric [C02l in relation to the global carbon cycle Glob Chang BioI 1243-274

Appel T 1998 Non-biomass soil organic N the substrate for N minshyeralization flushes following soil drying-rewetting and for organic N rendered CaClrextractable upon soil drying Soil BioI Biochem 30 1445-1456

Austin A T L Yahdjian J M Stark J Belnap A Porporato U Norton D A Ravetta and SM Schaeffer 2004 Water pulses and biogeochemshyical cycles in arid and semiarid ecosystems Oecologia 141221-235

Ball B c A Scott and 1 P Parker 1999 Field N20 CO2 and CH4 fluxes in relation to tillage compaction and soil quality in Scotland Soil Till Res 5329-39

Berg w R Brunsch and I Pazsiczki 2006 Greenhouse gas emissions from covered slurry compared with uncovered during storage Agric Ecosyst Environ 112129-134

Birch H F 1958 The effect of soil drying on humus decomposition and nitrogen availability Plant Soil 109-31

Borken w E A Davidson K Savage J Gaudinski and S E Trumbore 2003 Drying and wetting effects on carbon dioxide release from organic horizons Soil Sci Soc Am J 671888-1896

Chan A S K and T B Parkin 200 I a Effect of land use on methane flux from soil J Environ Qual 30786-797

Chan A S K and T B Parkin 200 I b Methane oxidation and production in soils from natural and agricultural ecosystems J Environ Qual 301896-1903

Cheng w K Vagi H Sakai and K Kobayashi 2006 Effects of elevated atmospheric CO2 concentrations on CH4 and N20 emission from rice soil An experiment in controlled-environment chambers Biogeochemshyistry 77351-373

Cheng w K Vagi H Xu H Sakai and K Kobayashi 2005 Influence of elevated concentrations of atmospheric CO2 on CH4 and CO2 entrapped in rice-paddy soil Chern Geol 21815-24

Cheng w K lnubushi K Vagi H Sakai and K Kobayashi 2001 Effect of elevated CO2 on biological nitrogen fixation nitrogen mineralization and carbon decomposition in submerged rice soil BioI Fertil Soils 347-13

Davidson E A P A Matson P M Vitousek R Riley K Dunkin G GarciaMendez and J M Mass 1993 Processes regulating soil emisshysions of NO and N20 in a seasonally dry tropical forest Ecology 74 130-139

Ernmerich W E 2003 Carbon dioxide fluxes in a semiarid environment with high carbonate soils Agric For Meteorol 11691-102

Follet R F and D S Schimel 1989 Effects oftillage practices on microbial biomass dynamics Soil Sci Soc Am J 531091-1096

Forster P V Ramaswamy P Artaxo T Berntsen R Betts D W Fahey J Haywood J Lean D C Lowe G Myhre J Nganga R Prinn G Raga



M Schulz and R Van Dorland 2007 Changes in atmospheric constitushyents and in radiative forcing In Climate Change 2007 The Physical Science Basis Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change S Solomon D Qin M Manning Z Chen M Marquis K B Averyt M Tignor and H L Miller (eds) Cambridge University Press Cambridge UK

Franzluebbers A 1 R L Haney C W Honeycutt H H Schomberg and E M Hons 2000 Flush of carbon dioxide following rewetting of dried soil relates to active organic pools Soil Sci Soc Am J 64613-623

Franzluebbers A J F M Hons and D A Zuberer 1998 In situ and potential CO2 evolution from a Fluventic Ustochrept in south-central Texas as affected by tillage and cropping intensity Soil Till Res 47303-308

Goudriaan J and H E de Ruiter 1983 Plant growth in response to CO2

enrichment at two levels of nitrogen and phosphorus supply I Dry matter leaf area and development Netherlands J Agric Sci 31 157-169

Groffman P M 1999 Carbon additions increase nitrogen availability in northern hardwood forest soils BioI Fertil Soils 29430-433

Hoque M M K Inubushi S Miura K Kobayashi H Y Kim M Okada and S Yabashi 2001 Biological denitrogen fixation and soil microbial biomass carbon as influenced by free-air carbon dioxide enrichment (FACE) at 3 levels of nitrogen fertilization in a paddy field BioI Fertil Soils 34453-459

Huxman T E K Snyder D Tissue A J Leffler K Ogle W T Pockman D R Sandquist D L Potts and S Schwinning 2004 Precipitation pulses and carbon fluxes in semiarid and arid ecosystems Oecologia 141 254-268

Inubushi K W Cheng S Aonuma M Hoque K Kobayashi S Miura H Y Kim and M Okada 2003 Effects of free-air CO2 enrichment (FACE) on CH4 emission from a rice paddy field Glob Chang BioI 91458-1464

Jacinthe P-A and W A Dick 1997 Soil management and nitrous oxide emissions from cultivated fields in southern Ohio Soil Till Res 41221-235

Johnson J M E A J Franzluebbers S L Weyers and D C Reicosky 2007 Agricultural opportunities to mitigate greenhouse gas emissions Environ Pollut 150107-124

Kaiser E-A and R Ruser 2000 Nitrous oxide emissions from arable soils in Germany-An evaluation of six long-term field experiments J Plant Nutr Soil Sci 163249-260

Keeling C D and T P Whorf 2001 Atmospheric CO2 records from sites in the SIO air sampling network In Trends A Compendium of Data on Global Change Carbon Dioxide Information Analysis Center Oak Ridge National Laboratory US Dept Energy Oak Ridge TN pp 14-21

Kern J S and M G Johnson 1993 Conservation tillage impacts on national soil and atmospheric carbon levels Soil Sci Soc Am 1 57200-210

Kessavalou A A R Mosier J W Doran R A Drijber D J Lyon and O Heinemeyer 1998 Fluxes of carbon dioxide nitrous oxide and methane in grass sod and winter wheat-fallow tillage management J Environ Qual 271094-1104

Kettunen R S Saarnio P J Martikainen and J Silvola 2006 Increase of N20 fluxes in agricultural peat and sandy soil under elevated CO2

concentration concomitant changes in soil moisture groundwater table and biomass production of Phleum pretense Nutr Cycl Agroecosyst 74175-189

Khalil M 1 and E M Baggs 2005 CH4 oxidation and N20 emissions at varied soil water-filled pore spaces and headspace CH4 concentrations Soil BioI Biochem 37 1785-1794

Kieft T L E Soroker and M K Fireston 1987 Microbial biomass response to a rapid increase in water potential when dry soil is wetted Soil BioI Biochem 19119-126

Leithold L 1976 The Calculus With Analytical Geometry 3rd Ed Harper amp Row New York NY

wwwsoilscicomI355

I

Smith et af Soil Science bull Volume 175 Number 7 July 2010

2004 Huxman et aI 2004 Prior et ai 2004) There are several hypotheses to explain this CO2 flux including the following oxidation of soil organic matter which becomes available as wetting and drying physically disrupts soil aggregates (Appel 1998) osmotic shock to the microbial biomass pool releasing organic matter that is used by the remaining microbes (Kieft et aI 1987) liberation of CO2 bound in soil carbonates (Emmerich 2003) and rainwater displacing CO2 that accumulates in soil pore space during dry periods (Huxman et aI 2004)

N20 Flux Although soil N20 flux in this study tended to be low

(range -15 to 534 g N20-N ha-1 day -1 with losses equaling 04-26 kg N20-N ha-1 year-1) values are in the range reported in the literature For example Zhijian et al (2008) reported emissions ranging from 07 to 394 g N20-N ha- 1 day-l for various crops In particular our values align with other studies examining unfertilized crops Liu et al (2005) reported N20 emissions of 13 g N20-N ha-1 day -1 in a com crop receiving no N fertilization with emissions being an order of magnitude higher in fertilized plots Kaiser and Ruser (2000) reported emissions ranging from 05 to 168 kg N20-N ha- 1 year- 1 for various crops with emissions from N-fixers being 13 to 30 kg N20-N ha- 1 year- 1

Moisture and N availability have been shown to be the main limiting factors for N20 production with C availability also regshyulating denitrification activity (GroJfman 1999 Kettunen et ai 2006) For example Jacinthe and Dick (1997) reported seashysonal N20 emissions ranging from 06 to 12 kg N20-N ha-1 in a comsoybean rotation study during a dry year and 16 to 37 kg N20-N ha-1 during a subsequent wetter growing season In our study rainfall during the sampling period tended to ocshycur frequently (40 events across 178 days of study) but in low amounts (range 003-427 mm average 16 mm with only 14 of the 40 days having greater than 5 mm) (Fig 2) suggesting that soil moisture conditions would not generally favor N20 production Furthermore soybean (being an N fixer) was grown without the addition of inorganic N fertilizer Relatively low rainfall with no N addition may have contributed to the low emissions and lack of significant differences in N20 flux between the two CO2 treatments

Tillage has been shown to increase N mineralization and thus gaseous losses of N through soil aeration soil moisture evaporation and accessibility of crop residues to soil microbes (Follet and Schimel 1989 Woods 1989) Gaseous losses of N have also been observed under no-till because of increased denitrification (Ball et aI 1999) In general management had little impact on soil N20 flux in our study Despite the fact that soil N20 flux was higher under conventional management on a few dates these differences were numerically small and did not affect seasonal N20 loss Liu et al (2006) also reported that emissions tended to be slightly higher under conventional tillage (12 g N20-N ha-1 day-I) compared with no-till (07 g N20-N ha -1 day - 1) for com grown without fertilizer additions A reshyview of the literature (Six et aI 2004) shows that N20 flux after conversion to no-till can depend greatly on the length of time of adoption of the new practice that is after 5 and 10 years noshytill had higher net N20 flux than conventional systems but after 20 years this trend was reversed They also point out that there remains a high degree of uncertainty around these estimates

CH4 Flux Most of agricultures contribution of CH4 flux results from

growing rice and from animal production whereas row crop agriculture tends to contribute little and can sometimes act as a

354 I wwwsoilscicom

sink (Johnson et ai 2007) Methane flux in our study was highly variable (range -793 to 2441 g CH4-C ha- 1 day-I) and was negative (sink) in about equal samplings as positive (source) although values were most often not different from zero Others have reported similar high levels of variability in CH4 flux (Chan and Parkin 200Ia)

Conservation management systems have frequently been shown to act as sinks for CH4 (Chan and Parkin 200 I b Berg et ai 2006 Johnson et ai 2007) In our study the conservashytion system showed negative flux rates (ie sink) on six sample dates as well as for the seasonal totai Likewise the conventional system also exhibited negative fluxes on five sample dates However C~ fluxes (whether posi tive or negative) generally did not differ from zero The conventional system had higher CH4

flux only on one date and the seasonal totals did not differ beshytween the two management systems In general elevated CO2

tended to have lower soil C~ flux but this difference was sigshynificant only on two dates and did not impact the seasonal toshytals Similar to the management effects both CO2 treatments had negative C~ fluxes on about half the sampling dates Methane is produced under anaerobic conditions (eg during rice proshyduction) and elevated CO2 can enhance CH4 flux in rice sysshytems (Cheng et aI 2001 2005 Hoque et aI 2001) In contrast to rice row crop agriculture rarely exists under anaerobic condishytions and is therefore unlikely to be a major contributor to CH4 production Although agricultural soils can act as a sink for C~ (Chan and Parkin 200Ib) soil in our study was neither a source nor sink for C~ regardless of management or atmoshyspheric CO2 concentration

Global Warming Potential In our study GWP was driven by the flux of CO2 This is

supported by the fact that there were no significant season-long differences in N20 or CH4 flux This contention is also supshyported by the fact that soil CO2 flux accounted for 97 to 99 of GWP across all treatment combinations Our results indicate that elevated atmospheric CO2 increased GWP In addition conventional management tended to have higher GWP than did the conservation system with the bulk of this increase related to soil CO2 flux during the tillage event These results are consisshytent with previous reports (Johnson et ai 2007 Berg et ai 2006 Chan and Parkin 2001b) which show that the GWP in conservation systems is lower than in conventional systems

CONCLUSIONS The objective of this study was to evaluate soil flux ofGHG

(C02 N20 and CH4) from conservation and conventional management systems that had been under the influence of eleshyvated atmospheric CO2 for 10 years Although data were colshylected only on 13 sampling dates in the final year of study (and these values are not intended to represent total actual soil GHG flux) this study is the first to show the qualitative effects of agricultural management under current (ambient) and future (elevated) atmospheric CO2 conditions on soil trace gas flux Elevated atmospheric CO2 and conventional management inshycreased soil CO2 flux Flux of both N20 and CH4 remained low throughout most of the growing season and rarely showed difshyferences caused by atmospheric CO2 level or land management (conventional vs conservation) Although infrequent differences in flux of CH4 and N20 were observed the seasonal GWP of these gases was not significantly affected by either treatment In our study GWP was increased by both elevated CO2 and conshyventional management and this increase was caused by inshycreased soil CO2 flux It has been suggested (Li et ai 2005) that land management (eg conservation vs conventional) will


1

Smith et af



(range -15 to 534 g N20-N ha -1 day -1 with losses equaling 04-26 kg N20-N ha -1 year -1) values are in the range reported in the literature For example Zhijian et al (2008) reported emissions ranging from 07 to 394 g N20-N ha- 1 day-l for various crops In particular our values align with other studies examining unfertilized crops Liu et al (2005) reported N20 emissions of 13 g N20-N ha -1 day -1 in a com crop receiving no N fertilization with emissions being an order of magnitude higher in fertilized plots Kaiser and Ruser (2000) reported emissions ranging from 05 to 168 kg N20-N ha- 1 year- 1 for various crops with emissions from N-fixers being 13 to 30 kg N20-N ha- 1 year- 1

Moisture and N availability have been shown to be the main limiting factors for N20 production with C availability also regshyulating denitrification activity (GroJfman 1999 Kettunen et ai 2006) For example Jacinthe and Dick (1997) reported seashysonal N20 emissions ranging from 06 to 12 kg N20-N ha -1 in a comsoybean rotation study during a dry year and 16 to 37 kg N20-N ha -1 during a subsequent wetter growing season In our study rainfall during the sampling period tended to ocshycur frequently (40 events across 178 days of study) but in low amounts (range 003-427 mm average 16 mm with only 14 of the 40 days having greater than 5 mm) (Fig 2) suggesting that soil moisture conditions would not generally favor N20 production Furthermore soybean (being an N fixer) was grown without the addition of inorganic N fertilizer Relatively low rainfall with no N addition may have contributed to the low emissions and lack of significant differences in N20 flux between the two CO2 treatments

Tillage has been shown to increase N mineralization and thus gaseous losses of N through soil aeration soil moisture evaporation and accessibility of crop residues to soil microbes (Follet and Schimel 1989 Woods 1989) Gaseous losses of N have also been observed under no-till because of increased denitrification (Ball et aI 1999) In general management had little impact on soil N20 flux in our study Despite the fact that soil N20 flux was higher under conventional management on a few dates these differences were numerically small and did not affect seasonal N20 loss Liu et al (2006) also reported that emissions tended to be slightly higher under conventional tillage (12 g N20-N ha -1 day-I) compared with no-till (07 g N20-N ha -1 day - 1) for com grown without fertilizer additions A reshyview of the literature (Six et aI 2004) shows that N20 flux after conversion to no-till can depend greatly on the length of time of adoption of the new practice that is after 5 and 10 years noshytill had higher net N20 flux than conventional systems but after 20 years this trend was reversed They also point out that there remains a high degree of uncertainty around these estimates



354 I wwwsoilscicom















REFERENCES






















enrichment at two levels ofnitrogen and phosphorus supply I Dry matter leaf area and development Netherlands J Agric Sci 31 157-169










Kessavalou A A R Mosier J W Doran R A Drijber D J Lyon and O Heinemeyer 1998 Fluxes of carbon dioxide nitrous oxide and

methane in grass sod and winter wheat-fallow tillage management J Environ Qual 271094-1104






wwwsoilscicomI355

1

I

I I I I I I

TECHNICAL ARTICLE

Clinoptilolite Zeolite Influence on Inorganic Nitrogen in Silt Loam and Sandy Agricultural Soils

David D Tarkalson and James A Ippolito

Abstract Development of best management practices can help imshy

prove inorganic nitrogen (N) availability to plants and reduce nitrateshy

nitrogen (N03 -N) leaching in soils This study was conducted to

determine the influence of the zeolite mineral c1inoptilolite (CL) addishy

tions on N03 - N and ammonium-nitrogen (NH4 - N) in two common

Pacific Northwest soils The effects of CL application rate (up to

269 Mg ha -1) either band applied or mixed with a set rate of N fertilshy

izer on masses of N03 - Nand NH4 - N in leachate and soil were inshy

vestigated in a column study using a Portneuf silt loam (coarse-silty

mixed mesic Durixerollic Caliciorthid) and a Wolverine sand (Mixed

frigid Xeric Torripsamment) All treatments for each soil received a

uniform application of N from urea fertilizer with fertilizer banded

or mixed with CL In the Portneuf soil band application of CL and

N contained 109 more total inorganic N (N03 - N + NH4 - N) in the

soilleachate system compared with mixing In both soils CL application

rate influenced the quantity ofN03 - Nand NH4 - N in the leachate and

soil Application of CL at rates of 67 to 134 Mg ha -1 resulted in the

conservation of inorganic N in the soils Band applying CL and N seems

to conserve available inorganic N in the soil compared with mixing CL

and N possibly because of decreased rates of microbial immobilization nitrification and denitrification

Key words Zeolite clinoptilolite nitrogen ammonium nitrate

(Soil Sci 2010175 357-362)

N itrogen (N) from fertilizers is needed to optimize and sustain crop production in agronomic systems but is susceptible

to leaching and denitrification loss from soils Nitrogen losses caused by leaching and denitrification from agricultural land especially in sandy soils are an environmental and economic concern (Perrin et aI 1998) Nitrogen loss from irrigated cropland can significantly contribute to nitrate levels in surface water and groundwater and can subsequently lead to waterway impainnent and eutrophication On a national scale agriculture accounts for 50 and 60 of impaired lakes and rivers reshyspectively (US EPA 2006) Thus preventing off-site nutrient movement is of paramount importance

A means ofiessening off-site N movement into waters and in particular N from land-applied N fertilizer is by application timing and placing N fertilizers in bands below the soil surface For example band application ofurea-N and anhydrous NH3 - N in moist soil will result in less NH3 - N volatilization losses compared with surface applications because of the ability of moist soils to retain ammonium-nitrogen (NH4 - N) and a greater distance before it reaches the atmosphere at the soil surface (Bouwmeester et aI 1985 Tisdale et aI 1985) Band applica-

USDA-ARS NWISRL Kimberly ID 83301 Dr Tarkalson is corresponding author E-mail davidtarkalsonusdaarsgov Received February 9 2010 Accepted for publication May I I 2010 Copyright copy 2010 by Lippincott Williams amp Wilkins ISSN 0038-075X 001 101097SS0bOI3e318Ie77ldl


tion of N fertilizers also removes it from surface runoff pathshyways Williams et al (2003) broadcast or band applied 350 kg of urea-N ha -1 approximately 3 weeks after sowing spinach (Spinacea oleracea L) followed by a 50-kg N ha -1 (again broadcast or band) 4 weeks later The authors noted that N leaching losses were greater with the broadcast fertilizer treatshyment (246 kg N ha -1 lost) as compared with banded (186 kg N ha -1 lost) Prasertsak et al (2002) either surface applied or drilled N-labeled urea 3 to 4 days after sugarcane (Saccharum officinarum L) harvest Although banding increased denitrifishycation and leaching losses as compared with surface application the total N loss was reduced from 591 to 456 with drilshyling as compared with surface application resulting in an extra 10 of applied N assimilated in the crop These management practices have been studied and introduced to directly or indishyrectly reduce N leaching in many agricultural systems However other new technologies associated with soil conditioners such as zeolite minerals have the potential to further reduce soil N leaching losses

Zeolites are naturally occurring aluminosilicate minerals (Kithome et aI 1998) More than 50 different types of zeolite minerals have been found (Tsitsishvili et aI 1992) They are composed of tectosilicates with isomorphous substitution of At3 and Si+4 and have high cation exchange capacities (CEC) (Perrin et aI 1998) because the clinoptilolite (CL) framework structure consists of interlinked four and five tetrahedral rings that create a layer between these layers are 8 and 10 open tetshyrahedral ring channels (Vaughan 1978) This open structure leads to increased CL surface area and has been measured at 925 x 105 m2 kg -1 (Kithome et aI 1998) Consequently inshycreased surface area produces a material with increased CEC The theoretical CEC of the zeolite mineral CL is 220 cmolc kg -1

(Ming and Mumpton 1989) Furthennore the structure of CL makes the mineral highly selective for K+ and NH4 + and less selective for Na + and divalent cations such as Ca +2 (Perrin et aI 1998) Theoretically the affinity of CL for NH4 + along with CL open mineral structure can potentially protect NH4 + from mishycrobial access and thus reduce nitrification rates

A number of research projects have shown increased growth andor yield of a variety of crops caused by either an effect of zeolites on improved N use efficiency or reduced NH4 + toxicity (Huang and Petrovic 1994 Minato 1968 Torri 1978 Moore et aI 1982 Stoilov and Popov 1982) Research evalushyating the effect of CL on NH4 - N and nitrate-nitrogen (N03 - N) leaching through soil has also been reported MacKown and Tucker (1985) found that mixing CL into a loamy sand at rates of 50 105 or 210 Mg ha -1 with a constant rate of ammoshynium sulfate applied at 440 kg NH4 - N ha -1 reduced NH4 - N leaching through columns compared with a control Nitrate-N was not measured because of the addition of a nitrification inshyhibitor with the N source However Huang and Petrovic (1994) found that mixing CL into simulated sand-based golf course greens at a rate equal to 10 of the soil mass (414 Mg ha -1) reduced N03 - Nand NH4 - N leaching through lysimeters compared with a control The purpose of the present study was

wwwsoilscicomI357


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Prior S A D C Reicosky D W Reeves G B Runion and R L Raper 2000 Residue and tillage effects on planting implement-induced shortshyterm CO2 and water loss from a loamy sand soil in Alabama Soil Till

Res 54197-199

Prior S A H H Rogers G B Runion H A Torbert and D C Reicosky 1997 Carbon dioxide-enriched agro-ecosystems Influence of tillage on short-term soil carbon dioxide efflux J Environ Qual 26244-252

Prior S A G B Runion H H Rogers and F 1 Arriaga 2010 Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exshyzchange in conventional and no-tillage systems 1 Environ Qual

39596-608

Prior S A G B Runion H H Rogers T A Torbert and D W Reeves 2005 Elevated atmospheric CO2 effects on biomass production and soil carbon in conventional and conservation cropping systems Glob Chang

BioI 11 657-665

356 I wwwsoilscicom

Reicosky D C 1997 Tillage induced CO 2 emission Nutr Cycl

Agroecosyst 49273-285

Reicosky D c D W Reeves S A Prior G B Runion H H Rogers and R L Raper 1999 Effects ofresidue management and controlled traffic on carbon dioxide and water loss Soil Till Res 52153-165

Rogers H H and R C Dahlman 1993 Crop responses to CO2 enrichment

Vegetatio 10411 05 117-131

Rogers H H W W Heck and A S Heagle 1983 A field technique for the study of plant responses to elevated carbon dioxide concentrations Air

PoIlu Control Assoc 1 342-44

Rogers H H G B Runion and S V Krupa 1994 Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere

Environ Pollut 83155-189

Runion G B S A Prior D W Reeves H H Rogers D C Reicosky A D Peacock and D C White 2004 Microbial responses to wheel-traffic in conventional and no-tillage systems Commun Soil Sci Plant Anal

352891-2903

Runion G B H A Torbert S A Prior and H H Rogers 2009 Effects of elevated atmospheric carbon dioxide on soil carbon in terrestrial ecosystems of the southeastern US In Soil Carbon Sequestration and the Greenhouse Effect 2nd Ed R Lal and RF Follett (eds) SSSA Special Publication No 57 ASA CSSA SSSA

Madison WI pp 233-262

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10155-160

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Torbert H A S A Prior H H Rogers and C W Wood 2000 Review of elevated atmospheric COz effects on agro-ecosystems Residue decomshyposition processes and soil carbon storage Plant Soil 22459-73

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Programs (6207J) Washington DC

Verburg P S 1 A Gorissen and W 1 Arp 1998 Carbon allocation and decomposition of root-derived organic matter in a plant-soil system of Calluna vulgaris as affected by elevated CO2 Soil BioI Biochem

301251-1258

Vose 1 M K J Elliot D W Johnson D T Tingey and M G Johnson 1997 Soil respiration response to three years of elevated CO2 and N fertilization in ponderosa pine (Pinus ponderosa Doug ex Laws) Plant

Soil 190 19-28

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Zak D R K S Pregitzer J S King and W E Holmes 2000 Elevated atmospheric CO2 fine roots and the response of soil microorganisms A review and hypothesis New Phytol 147201-222

Zhijian M u S D Kimura Y Toma and R Hatano 2008 Nitrous oxide fluxes from upland soils in central Hokkaido Japan J Environ Sci 201312-1322

Ziska L H T B Moya R Wassmann O S Namuco R S Lantin 1 8 Aduna E Abao Jr K F Bronson H U Neue and D Olszyk 1998 Long-term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice Glob Chang BioI 4657-665


J~

I I

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I



RESULTS






When totaled across the growing season soil CO2 flux was significantly higher under elevated (439 Mg COz-C ha -I) than ambient (334 Mg COz-C ha -I) atmospheric CO2 conditions Similarly the conventional system (419 Mg COz-C ha -I) had significantly higher seasonal soil CO2 flux than did the consershyvation system (353 Mg COz-C ha- I

)

N20 Flux There was no main effect of elevated CO2 on soil N20 flux




When totaled across the growing season there were no significant differences in soil N20 flux for the CO2 treatment (ambient 2914 g N20-N ha - elevated 8912 g N20-N ha -I)

Similarly management did not have a significant effect on soil N20 flux (conventional 4576 g N20-N ha -I conservation 7250 g N20-N ha -I) Although the interaction of CO2 and management on seasonal N20 flux was not significant it is inshyteresting to note that flux in the conservation system was about


Variable t

CO2 N20 CH4


115 0460 0932 0653 0925 0718 0682 0019 0183 0141 131 0010 0101 0324 0404 0237 0218 0802 0417 0630 153 0666 lt0001 0204 0411 0014 0135 0720 0642 0904 173 0016 0093 0816 0221 0477 0616 0960 0934 0419 180 0006 0110 0203 0346 0198 0094 0030 0325 0648 187 0093 0655 0645 0362 0340 0387 0102 0306 0833 194 0057 0146 0593 0358 0348 0330 0955 0725 0361 215 0171 0662 0226 0597 0400 0559 0523 0236 0407 229 0062 0087 0296 0383 0048 0694 0435 0329 0359 250 0007 0250 0064 0216 0395 0108 0219 0381 0853 264 0079 0362 0750 0638 0014 0269 0493 0016 0044 278 0682 0668 0242 0643 0433 0967 0518 0085 0457 292 0049 0309 0744 0577 0432 0210 0993 0509 0340 Total 0002 0043 0127 0281 0617 0389 0946 0224 0174

Prgt F statistics Bold represents significance tOOY day of year CO2 carbon dioxide in kg COrC ha -[ day -I N20 nitrous oxide in g N20-N ha -[ day -I C~ methane in g C~-C ha -Iday -I













350 I wwwsoilscicom

grain sorghum fertilizer N was applied at a rate of 34 kg N ha -I shortly after planting and an additional 10 1 kg N ha -I was applied 30 days after planting For wheat fertilizer N was apshyplied at planting (34 kg N ha -I) 35 months after planting

I(674 kg N ha -I) and 45 months after planting (34 kg N ha- ) Because clover soybean and sunn hemp are nitrogen fixers they received no fertilizer N however seeds were inoculated with commercial Rhizobium (Nitragin Co Milwaukee WI) beshyfore planting Cover crops and sorghum were terminated with glyphosate (N-[phosphonomethyl] glycine) 10 days before plantshying the following crop to prevent regrowth All operations previshyously described were also conducted on all nonexperimental areas to ensure uniform treatment of areas bordering the study plots Rainfall was measured on-site throughout the study period





1

Smith et al











350 I wwwsoilscicom










RESULTS






)








Variable t

CO2 N20 CH4


115 0460 0932 0653 0925 0718 0682 0019 0183 0141 131 0010 0101 0324 0404 0237 0218 0802 0417 0630 153 0666 lt0001 0204 0411 0014 0135 0720 0642 0904 173 0016 0093 0816 0221 0477 0616 0960 0934 0419 180 0006 0110 0203 0346 0198 0094 0030 0325 0648 187 0093 0655 0645 0362 0340 0387 0102 0306 0833 194 0057 0146 0593 0358 0348 0330 0955 0725 0361 215 0171 0662 0226 0597 0400 0559 0523 0236 0407 229 0062 0087 0296 0383 0048 0694 0435 0329 0359

I 250 264

0007 0079

0250 0362

0064 0750

0216 0638

0395 0014

0108 0269

0219 0493

0381 0016

0853 0044

I 278 0682 0668 0242 0643 0433 0967 0518 0085 0457

I 292 Total

0049 0002

0309 0043

0744 0127

0577 0281

0432 0617

0210 0389

0993 0946

0509 0224

0340 0174


I

1 I


I I

I I

I I


40

30

20 co J

y i 10 ()

CI

0

A -10

40

30

c 20 co J ()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02 1 3 u ~ 01

E l

~



_Rainfall

--+--- Conventional

--tr- Conservation

100 125 150 175 200 225 250 275 300

c Day of Year

120

100

80 E sect

60 c

OJ 40 c

20










DISCUSSION





wwwsoilscicomI353



50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

50000 c

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

12004 _Rainfall


1 03 C 80 Ec sect0 () 60 ll

02 ~

c co OJ







352 I wwwsoilscicom

01

20

125 150 175 200 225 250 275

Day of Year





60 ~Ambient

50 C

co 40

J 30Z

~ 20Z CI

10

0

A -10

70

60

50

40

co J

30Z 6 Z 20

CI 10

0

B -10


04 120

1 _Rainfall


80 Ell c sect0

60 ll c 02

cco OJ3 40 c u 01Oi

20E l (5 gt 0

100 125 150 175 200 225 250 275 300 0

C Day of Year



J~

Smith et al


60000 ~Ambient

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

c 50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

04 120

ME _Rainfall


1 03 C 80 E c sect 0 ()

02 60 ~


125 150 175 200 225 250 275

C Day of Year






352 I wwwsoilscicom






60 ~Ambient

50 C

40 co

J

Z 30

~ 20 Z CI

10

0

A -10


60 --ltgt-- Ambient

50

40

co J

30 Z 6

20 Z CI

10

0

B -10

04 120

1 _Rainfall


- 03 c


100 125 150 175 200 225 250 275 300

C Day of Year



--tr- Conservation

80

60

40

20


100 125 150 175 200 225 250 275 300

c Day of Year



DISCUSSION





wwwsoilscicomI353

40

30

20co

J

y i 10 ()

CI

0

A -10

40

30

c co 20 J

()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02

1 3 u ~ 01

E l

~

FIG 3



_Rainfall

--+--- Conventional


120

100

E sect

c

OJc




I -95 g CH4-C ha -1)





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REFERENCES







































wwwsoilscicomI355

I









354 I wwwsoilscicom










1

Smith et af








354 I wwwsoilscicom















REFERENCES







































wwwsoilscicomI355

1

I

I I I I I I

TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~

Smith et al











350 I wwwsoilscicom










RESULTS






)








Variable t

CO2 N20 CH4


115 0460 0932 0653 0925 0718 0682 0019 0183 0141 131 0010 0101 0324 0404 0237 0218 0802 0417 0630 153 0666 lt0001 0204 0411 0014 0135 0720 0642 0904 173 0016 0093 0816 0221 0477 0616 0960 0934 0419 180 0006 0110 0203 0346 0198 0094 0030 0325 0648 187 0093 0655 0645 0362 0340 0387 0102 0306 0833 194 0057 0146 0593 0358 0348 0330 0955 0725 0361 215 0171 0662 0226 0597 0400 0559 0523 0236 0407 229 0062 0087 0296 0383 0048 0694 0435 0329 0359

I 250 264

0007 0079

0250 0362

0064 0750

0216 0638

0395 0014

0108 0269

0219 0493

0381 0016

0853 0044

I 278 0682 0668 0242 0643 0433 0967 0518 0085 0457

I 292 Total

0049 0002

0309 0043

0744 0127

0577 0281

0432 0617

0210 0389

0993 0946

0509 0224

0340 0174


I

1 I


I I

I I

I I


40

30

20 co J

y i 10 ()

CI

0

A -10

40

30

c 20 co J ()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02 1 3 u ~ 01

E l

~



_Rainfall

--+--- Conventional

--tr- Conservation

100 125 150 175 200 225 250 275 300

c Day of Year

120

100

80 E sect

60 c

OJ 40 c

20










DISCUSSION





wwwsoilscicomI353



50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

50000 c

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

12004 _Rainfall


1 03 C 80 Ec sect0 () 60 ll

02 ~

c co OJ







352 I wwwsoilscicom

01

20

125 150 175 200 225 250 275

Day of Year





60 ~Ambient

50 C

co 40

J 30Z

~ 20Z CI

10

0

A -10

70

60

50

40

co J

30Z 6 Z 20

CI 10

0

B -10


04 120

1 _Rainfall


80 Ell c sect0

60 ll c 02

cco OJ3 40 c u 01Oi

20E l (5 gt 0

100 125 150 175 200 225 250 275 300 0

C Day of Year



J~

Smith et al


60000 ~Ambient

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

c 50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

04 120

ME _Rainfall


1 03 C 80 E c sect 0 ()

02 60 ~


125 150 175 200 225 250 275

C Day of Year






352 I wwwsoilscicom






60 ~Ambient

50 C

40 co

J

Z 30

~ 20 Z CI

10

0

A -10


60 --ltgt-- Ambient

50

40

co J

30 Z 6

20 Z CI

10

0

B -10

04 120

1 _Rainfall


- 03 c


100 125 150 175 200 225 250 275 300

C Day of Year



--tr- Conservation

80

60

40

20


100 125 150 175 200 225 250 275 300

c Day of Year



DISCUSSION





wwwsoilscicomI353

40

30

20co

J

y i 10 ()

CI

0

A -10

40

30

c co 20 J

()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02

1 3 u ~ 01

E l

~

FIG 3



_Rainfall

--+--- Conventional


120

100

E sect

c

OJc




I -95 g CH4-C ha -1)





J~





REFERENCES







































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354 I wwwsoilscicom










1

Smith et af








354 I wwwsoilscicom















REFERENCES







































wwwsoilscicomI355

1

I

I I I I I I

TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








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40

30

20 co J

y i 10 ()

CI

0

A -10

40

30

c 20 co J ()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02 1 3 u ~ 01

E l

~



_Rainfall

--+--- Conventional

--tr- Conservation

100 125 150 175 200 225 250 275 300

c Day of Year

120

100

80 E sect

60 c

OJ 40 c

20










DISCUSSION





wwwsoilscicomI353



50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

50000 c

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

12004 _Rainfall


1 03 C 80 Ec sect0 () 60 ll

02 ~

c co OJ







352 I wwwsoilscicom

01

20

125 150 175 200 225 250 275

Day of Year





60 ~Ambient

50 C

co 40

J 30Z

~ 20Z CI

10

0

A -10

70

60

50

40

co J

30Z 6 Z 20

CI 10

0

B -10


04 120

1 _Rainfall


80 Ell c sect0

60 ll c 02

cco OJ3 40 c u 01Oi

20E l (5 gt 0

100 125 150 175 200 225 250 275 300 0

C Day of Year



J~

Smith et al


60000 ~Ambient

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

c 50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

04 120

ME _Rainfall


1 03 C 80 E c sect 0 ()

02 60 ~


125 150 175 200 225 250 275

C Day of Year






352 I wwwsoilscicom






60 ~Ambient

50 C

40 co

J

Z 30

~ 20 Z CI

10

0

A -10


60 --ltgt-- Ambient

50

40

co J

30 Z 6

20 Z CI

10

0

B -10

04 120

1 _Rainfall


- 03 c


100 125 150 175 200 225 250 275 300

C Day of Year



--tr- Conservation

80

60

40

20


100 125 150 175 200 225 250 275 300

c Day of Year



DISCUSSION





wwwsoilscicomI353

40

30

20co

J

y i 10 ()

CI

0

A -10

40

30

c co 20 J

()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02

1 3 u ~ 01

E l

~

FIG 3



_Rainfall

--+--- Conventional


120

100

E sect

c

OJc




I -95 g CH4-C ha -1)





J~





REFERENCES







































wwwsoilscicomI355

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354 I wwwsoilscicom










1

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354 I wwwsoilscicom















REFERENCES







































wwwsoilscicomI355

1

I

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TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~

Smith et al


60000 ~Ambient

50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

A 0


60000 ~Ambient

c 50000

co 40000 J ()

c5 30000 ()

CI 20000

10000

B 0

04 120

ME _Rainfall


1 03 C 80 E c sect 0 ()

02 60 ~


125 150 175 200 225 250 275

C Day of Year






352 I wwwsoilscicom






60 ~Ambient

50 C

40 co

J

Z 30

~ 20 Z CI

10

0

A -10


60 --ltgt-- Ambient

50

40

co J

30 Z 6

20 Z CI

10

0

B -10

04 120

1 _Rainfall


- 03 c


100 125 150 175 200 225 250 275 300

C Day of Year



--tr- Conservation

80

60

40

20


100 125 150 175 200 225 250 275 300

c Day of Year



DISCUSSION





wwwsoilscicomI353

40

30

20co

J

y i 10 ()

CI

0

A -10

40

30

c co 20 J

()

10 ()

CI

0

B -10

04

1 E - 03 c ll c 0

c 02

1 3 u ~ 01

E l

~

FIG 3



_Rainfall

--+--- Conventional


120

100

E sect

c

OJc




I -95 g CH4-C ha -1)





J~





REFERENCES







































wwwsoilscicomI355

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354 I wwwsoilscicom










1

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354 I wwwsoilscicom















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1

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TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~





REFERENCES







































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354 I wwwsoilscicom










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I

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TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~

Smith et af








354 I wwwsoilscicom















REFERENCES







































wwwsoilscicomI355

1

I

I I I I I I

TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~

I I I I I I

TECHNICAL ARTICLE
























(Soil Sci 2010175 357-362)










wwwsoilscicomI357











Bot 461561-1567





Change Res 4039-80


10387-339








Res 54197-199



39596-608


BioI 11 657-665

356 I wwwsoilscicom





Vegetatio 10411 05 117-131






352891-2903




10155-160







301251-1258


Soil 190 19-28








J~

effects of elevated co2 and agricultural management on ......integration technique (i.e.,...

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