Understanding Nutrient & Sediment Loss at Saxon Homestead Farm - 6

Sediment Loss at Saxon Homestead Farm

Winter 2010/2011

Eric Cooley, Aaron Wunderlin and Dennis Frame UW-Extension/Discovery Farms

When precipitation falls on soil, the force of the raindrop impact can break up soil aggregates into smaller sand, silt and clay particles. As water travels over the soil in a runoff situation, these particles are more easily transported than if they were aggregated. The lack of vegetative cover, the use of excessive tillage and/or other soil disturbances enhance the potential for agricultural fields to have excessive levels

of sediment loss. Sediment loss has the potential to decrease crop production and can cause detrimental effects in aquatic environments (have negative impacts on water quality). This fact sheet will assess sediment loss in surface runoff and tile drainage at the Saxon Homestead Farm, LLC (SHF) and the factors affecting the observed sediment losses.

Figure 1. Surface water monitoring basins K1, K2 & K3 and tile water monitoring basin K4

Surface and tile water monitoringYear round surface water monitoring began at SHF in

October 2004 at three sites (K1, K2 & K3) and concluded in spring 2007. Subsurface tile water monitoring also began in December 2004 in one location (site K4) and was concluded at the end of November 2006. Roughly half a month of tile monitoring was missed during the first year due to the time required to install equipment (this missing data is annotated by an asterisk in graphs).

The upstream/downstream monitoring design was selected for this farm to determine the contributions of sediment and nutrients from the grazed paddocks and the SHF farmstead (building site). The water upstream of the farmstead comes from an area containing SHF grazed paddocks, forest and other cropland not under the control of SHF. The majority of the area between the upstream and downstream sites contained SHF grazed paddocks, but this area also contained the farmstead and a small amount of forested area (Figure 1). The water, sediment and nutrient loading monitored at the upstream site (K1) was subtracted from that measured at the downstream site (K2) and the result yields the contribution from the 146 acres of grazed paddocks and farmstead. A third monitoring site (K3) was installed in a road ditch that delivered water to an area very near the upstream site from an intensively tilled field not under control of SHF. This monitoring site was added to the study design to assess the impact of a different farming system that could potentially skew the results at the upstream site.

The agronomic details of cropping history for the field in K3 were not obtained because the operator was not part of the Discovery Farms Program. Information gathered from site visits and daily photographs at each site (SHF-3)

allowed for the basic cropping information to be assembled in Table 1. It is believed that tillage was performed with a moldboard plow in late fall and leveling with a disc was performed prior to planting. After the fall tillage was performed, surface residue was estimated to range from 0% to 10% based on the type of crop. Virtually no residue remained after tillage following soybeans and between 5% and 10% residue remained after corn harvested as grain.

The paddocks used by SHF both upstream of K1 and the areas between K1 and K2 had no tillage performed for approximately 10 years prior to the study. No tillage was performed on paddocks operated by SHF during the study

Water budget at SHF

Surface and tile sediment loss

until November 1, 2006 when approximately 40 acres of paddocks were tilled for reseeding just upstream of site K1. No agronomic data was collected from fields that were outside the control of SHF even though a small number of these fields contributed runoff to the monitoring stations. The only field where cropping data was collected for that which was not managed by SHF was the intensely tilled field contributing to site K3.

The drainage area of the upstream site was estimated to be 495 acres (Figure 1). The total drainage area of the downstream site was estimated to be 641 acres to give a resulting acreage between the upstream and downstream site of 146 acres. The third drainage area containing the intensively tilled field was estimated to be 17.6 acres. After

the original study design was installed, a fourth monitoring site (K4) was installed to measure water flowing through the tile drainage system. The tile site was paired with the downstream surface water site (K2) and it was determined that the drainage area was the same as the surface site at 641 acres. These basin sizes were utilized for yield calculations in this set of fact sheets.

For purposes of consistent organization, the data presented in Discovery Farm graduation reports is usually based on our definition of a field year (FY), which is typically the 12-month period from October 1 through September 30. Because of the lack of initial surface flow and the installation of the tile site in December, a modified field year was used for all the fact sheets in the SHF series. In addition, due to the high volume of earthwork that was performed for the install of the sites, early data (first few months) may be skewed due to the bare soil conditions in the established grassed waterways. The definition of a field year (FY), for these reports will be a 12-month period from

December 1 through November 30. The field year always represents the calendar year in which it ends, which means that the field year ending November 30, 2005, is the 2005 field year (FY2005).

In this report, precipitation is referred to as frozen (snow, hail, sleet, etc) and non-frozen (rain). Frozen precipitation was converted to its water equivalent using a conversion coefficient (0.06) so that frozen and non-frozen precipitation can be analyzed equally. The general trends for the study period had one low and one high year compared to the 30-year average of 29.8 inches (Figure 2).

Table 1. Cropping and tillage history at K3

Year Crop Harvest Date Tillage date

2004 Soybeans 11/7/2004 11/18/2004

2005 Soybeans 10/1/2005 11/24/2005

2006 Corn 10/10/2006 11/15/2006

The sediment loss that occurred from the grazed paddocks at SHF was minimal compared to the soil loss at other Discovery Farm sites. The soil loss for the grazed paddocks (K1 and K2) compared to the intensively tilled row crop field (K3) again showed lower soil loss (Figure 3). Losses in the tile drainage system were slightly higher when compared to other Discovery Farm sites. A portion of the low surface runoff volumes and elevated tile flow values may be attributed to the well developed preferential flow paths or tile blow outs that could transfer portions of the surface sediment to the tile.

The timing of sediment loss at SHF followed patterns that are typical of what has been seen at other monitoring sites. In FY05, the majority of the runoff occurred when the ground was frozen, thus soil loss was minimal. In FY06, most of the runoff occurred in May when the soil was not frozen, void of residue and had high soil moisture conditions (Figure 3); thus soil loss was significant. Evaluation of the timing of soil loss over the monitoring period shows that sediment movement during the frozen ground period is a much smaller fraction of total loss when compared to the non-frozen period (Figure 4). Visual

observations in FY05 (when the majority of frozen runoff happened), indicated that wind erosion during winter months may have resulted in increased frozen sediment losses at site K3. Just prior to multiple snowmelt conditions, snow stained with blowing sediment was observed in the field and ditch at this site. The bare soil conditions caused increased wind erosion and higher erosion potential when

Figure 2. Precipitation versus 30-year average and runoff

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Precip. K1 K3 K2 K4* Precip. K1 K3 K2 K4

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FY2005 (Dec. 2004 - Nov. 2005) FY2006 (Dec. 2005 - Nov. 2006)

Yearly Precipitation and Runoff (Dec. 2004 - Nov. 2006)

Fr. Precipitation (L.E.)

Non-Fr. Precipitation

Runoff K1, K3, K2

Flow K4

30-yr Avg. Precipitation (29.8)

6% 15% 4% 16% 11% 13% 7% 16%

% - percent of precipitation that ran off each basin

Add Add

Surface and tile sediment loss comparison

runoff occurred. During the same period wind erosion was not observed on the grazed paddocks.

During the non-frozen period, visual field observations showed increased transport of sediment at K3 as compared to the other sites. Runoff coming from K3 was darker and much more turbid when compared to runoff from the grazed paddocks (Figures 5). A distinct difference can be observed in the water coming in from K3 when mixed with the clear water from the paddocks just upstream of site K1 (Figure 6).

Of the 2.5 tons/acre of soil that was lost from the K3 site in FY06, over half came from one storm that occurred late

in the night on 5/27/06 and finished early in the morning on 5/28/06. A few days later, another storm came through during the morning of 5/30/06 and this storm contributed another 20% of the total sediment loss for the year. Between these two storms, approximately 2.1 tons of sediment per acre was lost from the field site at K3. Sheet, rill and gully erosion were observed during rain events and large amounts of sediment (soil) deposition were noted in the lower portion of the field (Figure 7). The deposition was so significant that emerging corn plants, up to five inches high, were buried in some locations by the soil deposits.

Figure 3. Annual suspended sediment loss during 2 years of monitoring

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Annual Suspended Sediment Loss

FY2005 (Dec. 2004 - Nov. 2005)

FY2006 (Dec. 2005 - Nov. 2006)

5000 lbs/acre

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Average Suspended Sediment Loss (Dec. 2004 - Nov. 2006)

Frozen Ground

Non-Frozen Ground

Figure 4. Average suspended sediment loss timing

An important aspect that needs to be kept in mind when designing management practices to reduce sediment loss from agricultural land is the pathways for sediment movement and loss. At SHF, because the monitoring of both surface runoff and tile flow was conducted at the same time, UW -Discovery Farms was able to simultaneously compare losses from both systems.

The tile drainage system was the major pathway for sediment loss in the two years of data collected at SHF (Figure 8). There are two factors that likely contributed to the low level of sediment loss through surface water

runoff when compared to tile flow. The first is the large volume of water that was transferred from the surface of the soil to the tile drainage system through preferential flow paths as identified in the previous graduation report (SHF-5). Sediment suspended in the runoff water is believed to have followed similar flow channels. The second factor that contributed to the low levels of sediment loss in surface runoff is the vegetative cover present on the grazed paddocks. The vegetative cover provided by the perennial grass protects the soil from erosion in the spring when fields planted to row crops typically experience high sediment movement as observed at the K3 site.

Figure 5. Runoff from site K3 Figure 6. K3 runoff mixing with cleaner water coming into site K1

3%

97%

2-yr Basin Average Total Sediment Loss

Surface (K2)

Tile (K4)

Surface: 15 lbs/acre/year average

Tile: 440 lbs/acre/year average

This material is based upon work supported by the National Institute of Food and Agriculture (NIFA), U.S. Department of Agriculture, under Agreement No. 2009-45045-05632. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

This fact sheet is part 6 of a 9 part series and can be found along with the rest of the fact sheets on the web at: www.uwdiscoveryfarms.org or by calling the UW-Discovery Farms Office at 715-983-5668.

© 2010 by the Board of Regents of the University of Wisconsin System. University of Wisconsin-Extension is an EEO/Affirmative Action employer and provides equal opportunities in employment and programming, including Title IX and ADA requirements. Publications are available in alternative formats upon request.

Figure 7. Rill and gully erosion observed from K3 field

The data presented in this article were provided by the U.S. Geological Survey as part of a cooperative agreement with the UW-Discovery Farms Program.

Conclusions➢ Sediment loss that occurred from the grazed paddocks at

SHF was minimal as compared to observed soil loss at other Discovery Farm sites and the intensively tilled row crop field monitored by site K3.

➢ The majority of sediment loss occurred during the non-frozen ground period, specifically during early spring rain events after the snowmelt period.

➢ The intensively tilled row crop field exhibited high soil movement in both visual observations and monitored water quality data. In a four-day period in the spring of 2006, loss exceeded two tons of sediment per acre.

➢ Visual observations and water quality data showed notable wind erosion and loss of sediment during the frozen ground period from the bare soil at the intensively tilled row crop field, K3.

➢ From concurrent monitoring of sediment leaving the farm, the major pathway was tile (97%) as compared to surface (3%). The protection offered by the continuous vegetative cover in the paddocks combined with preferential flow to tile likely combined for low surface sediment loss.

Figure 8. Average sediment loss leaving SHF during 2 years of monitoring

Intensive tillage leaves little surface residue at K3