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MICRONUTRIENTS ROBBING CORN YIELDS ON LONEWOOD SOIL Grove, J.H1.; Schwab, G.J.2; Thompson, E. Raymond3

1 UK Soil Management Agronomist, University of Kentucky, Lexington, KY, 405462UK Extension Agronomist, University of Kentucky, Lexington, KY, 40546

3Russell County Extension Agent for Agriculture, University of Kentucky, Russell Springs, KY, 42642

Fertilizer Applied R1 Leaf Tissue Analysis Grain

N P S B Cu Zn N P S B Cu Zn Yield

------------ kg ha-1 ------------- ------ g kg-1 ---- ---mg kg-1 ----Mg ha-1

67 100 56 6 29 3.4 2.0 3.8 7.5 19 16.0

67 100 56 6 26 2.9 1.6 3.5 8.8 11 15.9

67 40 20 2 30 2.6 1.8 4.3 9.0 15 14.2

67 40 22 1 28 2.6 1.9 4.5 8.5 14 13.9

67 22 2 30 2.1 2.1 4.5 11.3 17 11.6

67 22 1 30 1.8 2.1 6.3 11.0 15 10.0

67 22 5 29 1.6 1.9 4.3 10.5 21 9.5

67 22 22 29 1.8 2.0 4.8 11.5 41 9.5

67 22 28 1.8 2.1 4.3 10.8 15 9.2

67 22 6 3 30 1.6 2.0 4.3 11.8 18 8.5

LSD(0.10) NS 0.3 0.2 0.9 1.1 5 1.7

Application Tissue ConcentrationTreatment Rate Potassium Sulfur Boron Zinc Yield

kg ha-1 -------- g kg-1 -------- ------ mg kg-1 ------- Mg ha-1

Control 24 1.4 2.3 15 7.6Potassium 56 25 1.5 3.0 15 7.7

Zinc 22 25 1.6 3.5 24 8.3Sulfur 22 25 1.5 3.5 22 8.7Boron 1 24 1.5 5.0 14 7.6All Nutrients

25 1.5 4.0 29 8.0

LSD(0.10) N.S. NS 2.5 13 N.S.

Application Tissue ConcentrationTreatment Rate Potassium Sulfur Boron Zinc Yield

kg ha-1 ------- g kg-1 ------- ----- mg kg-1 ------ Mg ha-1

Control 23 2.7 9 21 2.2

Potassium 56 23 2.7 11 21 2.0

Zinc 22 22 2.8 9 38 2.1

Sulfur 22 23 3.0 9 17 2.6

Boron 1 22 2.7 42 20 2.5

All Nutrients 24 3.1 41 35 2.3

LSD(0.10) N.S. NS 30 13 N.S.

Table 2. Corn tissue nutrient concentration and grain yield in Russell2008. Numbers in red indicate concentrations below the establishedcritical level.

Table 3. Soybean tissue nutrient concentration and grain yield in2008. Numbers in red indicate concentrations below theestablished critical level.

Table 5. Corn tissue nutrient concentration and grainyield in 2009. Numbers in red indicate concentrationsbelow the established critical level. The green boxdenotes the control. Only one treatment surpassedminimum boron leaf concentrations.

Table 1. Stratification of Nutrients in Lonewood Soil UnderNo-tillage System

Materials and Methods

A study was designed in 2008 for the two siteswhere micronutrients and K2O were replicated incorn and soybeans on the Lonewood soil series.Corn plots were harvested by hand picking in 2008while the soybeans were collected by a plot combine.In 2009 and 2010 the UK corn plot harvester wasused. It was a dry crop season but micronutrientsdid impact crop performance. Soybean treatmentscould be distinguished from the untreated plots, butno yield response could be measured. The corn alsoproduced a visual difference but it was evident in theear development. A second ear compensated thepoorly developed first one and no significant yielddifferences could be demonstrated betweentreatments although one could easily determinewhere the check plots were. It appeared as though alate rain had mineralized boron just as the secondear began filling.

A second group of plots were established in 2009and 2010. Dr. Grove joined the investigation andexpanded research on zinc amendments.

Introduction

The site shown in Figure 1 is the location of oneof the two fields where a history of poor cornperformance was reported by the grower. Dr.Schwab and Thompson examined soil test data andcrop history with the grower and discoverednutrient trend patterns. Fertilizer and limeamendments had been applied according to AGR-1Lime and Nutrient Recommendations for 20 years.The soil pH seemed to be out of control, thereforethey expected to encounter issues with zinc sincezinc deficiencies had been documented inreplicated plots in the 1980’s on the same soilseries in Russell County. Ridge Land soils inRussell County have been plagued with low cationexchange capacity (CEC), Also, potassiumconcentrations seemed to be in decline over thedecades.

Abstract

Russell County experienced a reduction of itscorn acreage from 1982-2007 while soybean acresincreased. A grain farmer contacted the RussellCounty Agriculture Agent3 with a problem wheresome fields were yielding more bushels of soybeans(67) than corn (63) and corn yields were decliningover time. However, that community produced anaverage of 188 bushels per acre of corn in 2002.

Dr. Greg Schwab was contacted and he reviewedthe farmer’s crop history and designed a nutrientstudy. In 2008 replicated plots were established onthe worst-yielding fields that contained theLonewood soil series. Two other sites were addedin 2009 by Dr. Grove to study zinc soil amendments.

Three seasons of replicated studies revealed noimpact on soybean yields from treatments of zinc,boron, copper or sulfur.

Under extreme environmental conditions cornyields were reduced by the following nutrients inorder of importance: Zinc, Boron, Copper, andSulfur. These data are not cumulative since soilmoisture is a factor in determining which nutrient ismost limiting.

A protocol was developed to predict borondeficiencies in corn by tissue-testing soybeansduring the previous season. CEC is used to flagboron deficient soils. Liming recommendations weremodified to reduce copper & zinc deficiencies bycontrolling soil pH.

Depth CEC P2O5 pH Buf pH Zn K2O Mg BO CU

0-2" 8 142 6.2 7.0 2.8 309 128 0.4 0.76

2" - 4" 7 62 5.9 7.0 0.6 245 72 0.45 0.68

4" - 6" 6 58 5.8 7.0 0.8 182 62 0.27 0.82

Discussion

A low pH site near Russell Springs produced anextraordinary yield response to zinc of 50 bushels ofcorn per acre. No boron response was detected ateither site due to adequate soil moisture during cropdevelopment.

However, responses to zinc and boron weremeasured in 2010 in the high pH sites. Moreover,many fields outside the experimental area exhibiteddrastic yield reductions in dry soils where no boraxhad been applied. Barren cobs cut yields byunprecedented amounts. The Lonewood soilsresponded like they were devoid of boron.

The high pH sites continued to show significantresponses to zinc supplementation, but an expectedresponse to copper was measured.

Fine-textured soils are highly weathered and oftencontain low concentrations of nutrients like boron,copper and zinc. Furthermore, the Lonewood soilseries is not well buffered against changes in pH.Most of the series is characterized by CEC valuesbelow 7. Increases in organic matter greatly improvecrop performance.

Fragile soils that are poorly buffered may respondto lower pH thresholds than typical silt loamsbecause essential metals are more soluble as thesoil becomes acidic. Caution must be exercised tomaintain a pH above 6.2 for soybeans to supplyadequate molybdenum and phosphorus.

Conclusions

Soils of the upper Cumberland Plateau are atypical of the productive, silt loam soils of the Bluegrass State. One soil association is often deficient in organic matter and consequently nutrients that are recycled through organic matter include boron, copper, and zinc. The textural class also limits the cation exchange capacity and water-holding capacity. The typical cation exchange capacity of these soils is 7 meg/100g giving them a limited ability to buffer pH changes. Farmers have over-corrected the pH in favor of soybeans. The pH in some of these soils can remain lodged above pH 7 for many years. Add to that the stratification of nutrients under strict, continuous no-till and a high pH zone rich in phosphorus and organic matter occurs in the top two inches of the A horizon. The combination of high pH, low zinc concentration and high concentrations of P equate to zinc deficiency under wet soil conditions. Conversely, soils that are marginal in boron do not mineralize enough B from the organic matter during extreme dry weather.

A means to ameliorate the antagonisms of high pH, high concentrations of P2O5 and low micronutrient concentrations without tillage must be defined, since lowering the pH using soil amendments is too cost prohibitive. In some seasons, the addition of zinc sulfate or borax returns a crop response greater than the cost of application. Boron application rates are best determined by the leaf analyses of soybeans grown the previous year and CEC is a fair indicator of soil organic matter. Organic matter can be mineralized in years where there is adequate rainfall to supply boron.

Clearly, prevention of soils reaching 7 pH is needed, but better yet is to maintain 6.2 pH during the years when soybeans will be grown. Soils should be maintained in the acidic range for corn to insure adequate availability of zinc and copper while assuring the macronutrients are in adequate supply. Phosphorus should be available to corn when the pH is as low as 5.7. Nitrates are more available as the pH nears 6.0.

Current lime rates for grain crops in Kentucky target pH of 6.4, but they can be adjusted downward to 6.2 using the tables in AGR-1 Lime and Nutrient Recommendations. A smaller application of lime should be applied in the fall prior to soybeans or additions of sodium molybdate will have to be applied to insure the soybean rhizobia are adequately supplied. Lime rates for these soils will resemble fertilizer rates where a pH of 5.3 can rise to 6.4 with less than a ton of lime per acre. Most farmers and lime spreader applicators will resist

applying less than a ton of lime per acre every two years. Therefore, corn yields may continue to lag well below the state average while soybeans will continue to match or exceed the national average. Increases in corn yield will come when farmers correctly guess the weather pattern and apply enough of the right micronutrient.

Table 4. Micronutrients affecting corn and soybeanare most available between 5.8 and 6.2. Low CECsoils require more frequent & smaller lime applicationsto contain the pH within a narrow range. Molybdenumis deficient in soybean rhizobia when the pH dropsbelow 6.2. Metallic nutrients are more soluble in acidicsoils. Boron is also more available at low soil pH.

Figure 1 Over liming is an issue on these soils for corn growers

Figure 2 Plot Harvester Measuring Zinc Response in 2010

Figure 3 Many barren cobs were observed in the high pH plots in 2010.

Figure 4 In 2009 extremely high yields were measured in the low pH sites.