Does Grazing or Harvesting of Cover Crops Affect Soils and Crop Production? Assessment in Different Soil Types and Management Scenarios
The first year of this timely and interdisciplinary project was successfully completed. The project is being conducted on five representative sites including three on-farm sites and two research sites across a precipitation gradient in Nebraska. At each site, we had three treatments with three replications in a randomized complete block design. Treatments included: 1) control (non-grazed/non-harvested cover crop), 2) grazed/harvested cover crop, and 3) no cover crop under continuous corn, corn-soybean and corn-soybean-wheat rotations under no-till management. Corn was harvested as silage. At one on-farm site, cover crop was harvested (not grazed). The size of each treatment plot varied to accommodate farming operations. The control and cover crop plots were fenced and the area outside with cover crops was grazed. Winter rye cover crop was used at three sites, oats at one site, and mixture of brassicas and rye at one site. Continuous corn was used at three sites and corn-soybean at two sites. We worked closely with the producers who participated in the establishment of the experiment on their farms and managed cover crops.
Baseline data including soil texture, soil fertility, and other properties were collected. To this point, we have measured subsequent grain yield, cover crop biomass, and percent soil cover after grazing. We also measured soil structural and compaction parameters, water infiltration, and wind erosion potential. The first year results showed no negative effect of cover crop grazing or harvesting on main crop yields. Soil compaction did not change with grazing. Mixture of brassicas and rye increased water infiltration and improved soil structure (soil aggregate stability). At the on-farm site near North Platte, NE, grazing cover crop reduced water infiltration in spring. Wind erosion potential (dry soil aggregate stability) decreased at most sites under cover crops with and without grazing compared with control (no cover crop), indicating that cover crops can reduce wind erosion. Grazing cover crop did not affect soil fertility. Overall, the first year data showed no negative effect of grazing cover crops on crop yields and soil properties. The project is having a positive impact. We trained an undergraduate student (Rebecca Clay from Iowa State Univ) in summer 2016. We disseminated results in a field day in eastern Nebraska, Nebraska Summer Research Symposium, and the ASA-CSSA-SSSA International Annual Meetings in Phoenix, AZ. A graduate student (Philip Hinson) was recruited and will start in spring 2017 to help with the execution of this project.
During 2016, we focused on the following objectives:
- Measurement of grain yield, cover crop biomass, percent soil cover after grazing, and feed nutritive value under the different cover crop treatments.
- Assessment of soil structural, compaction, and water infiltration properties as affected by grazing cover crops.
- Assessment of wind erosion potential and soil fertility properties.
Work on other objectives mentioned in the proposal including economic analysis will begin in 2017.
We conducted this project on five representative sites including three on-farm sites and two research sites across a precipitation gradient in Nebraska. The three on-farm sites are located near Johnson, Firth, and North Platte, NE. The two research sites are located at Mead and North Platte, NE. The two research sites are at the University of Nebraska’s (UNL) Agricultural Research Development Center (ARDC) near Mead and UNL West Central Research and Extension Center, North Platte, NE. Three sites (Johnson, Firth, and Mead) are in eastern NE where precipitation is greater than the two sites (near North Platte) in western central Nebraska. Sites near Johnson and Mead, NE are rainfed and the sites near Firth and North Platte are irrigated. Soil textural classes include silty clay loam, silt loam, and sandy clay loam.
We established the sites in fall 2015. Then, we measured soil properties in spring 2016 and crop yields in fall 2016. At each site, there were three treatments with three replications in a randomized complete block design. The three treatments included the following: 1) non-grazed/non-harvested cover crop 2) grazed/harvested cover crop, and 3) no cover crop under continuous corn, corn-soybean and corn-soybean-wheat rotations under no-till management. Corn was harvested as silage. Cover crop was grazed in spring 2016 for about one month before planting the main crops. At the on-farm site near Firth, NE, cover crop was harvested (not grazed). The size of each treatment plot varied at each site to accommodate farming operations and preference of farmers. The control and cover crop plots were fenced when cover crop was growing, and then the area outside of the fence with cover crops was grazed. Winter rye cover crop was used at three sites, oats at Mead, NE, and mixture of brassicas and rye at Firth, NE. These differences reflect the farmer’s preference and purpose for cover cropping in their farms. We worked closely with the producers who participated in the planning and establishment of the experiment on their farm, planted cover crops, and managed cover crops.
In fall 2015, we collected soil samples from the 0 to 4 inch and 4 to 8 inch soil depths for the determination of baseline data including soil texture, soil fertility, and other properties. In spring 2016 after cover crop grazing and before planting main crops, we measured soil structural and compaction parameters, water infiltration, and wind erosion potential at each site using standard methods as discussed in the original proposal.
Data on soil compaction parameters such as soil bulk density and penetration resistance measured for the 0 to 4 inch and 4 to 8 inch soil depths indicated that, after one year of treatment, cover crop grazing had no significant effect on bulk density and penetration resistance at any of the sites. The lack of differences in soil compaction among cover crop grazing treatments for the first year of the study appears to be consistent with results from the literature on the subject.
Water infiltration measured in the field using double ring infiltrometers did not change except at the on-farm sites near Firth and North Platte, NE. At Firth, mixture of brassicas and rye increased water infiltration. At the on-farm site near North Platte, water infiltration decreased due to cover crop grazing in spring. Although not statistically, there was some trend for increased compaction at this site, which possibly reduced water infiltration.
We also measured wet soil aggregate stability (soil structural quality parameter) by wet sieving soil samples in the laboratory. Data showed that grazing cover crops did not affect wet aggregate stability, but at the on-farm site near Firth, NE, cover crop and cover crop harvesting increased soil aggregate stability similar to water infiltration. These results suggest that mixtures of brassicas with rye can improve water infiltration and improve wet soil aggregate stability and soil structural quality.
Crop yield measurements in fall 2016 showed no negative effect of grazing or harvesting cover crops on main crop yields. We also measured dry soil aggregate stability as an indicator of wind erosion potential in spring 2016. Wind erosion potential decreased at most sites under cover crops with and without grazing compared with control (no cover crop), which indicates that cover crops with and without grazing can reduce wind erosion potential. Grazing cover crop did not affect soil fertility. In general, the first year data show no negative effect of grazing cover crops on crop yields and soil properties. These results are highly promising for the use of cover crops as forage but more data from different years are needed to make conclusive recommendations.
Impacts and Contributions/Outcomes
The results from this project will have a larger impact in coming years. We have received many positive comments on this regional project. Farmers have expressed a lot of interest in the data. The first year data were reported in the following outreach opportunities in 2016.
- I gave a talk to about 60 farmers in Johnson, NE. September 7, 2016. Meeting organized by the University of Nebraska-Lincoln Extension, NRCS, University of Nebraska-Lincoln Extension in Nemaha County (Gary Lesoing). I presented the first year research results from this collaborative project regarding impacts of grazing/harvesting cover crops on soils and crop yields across five on-farm sites in Nebraska. Audience: farmers.
- I trained one undergraduate student (Rebecca Clay) from Iowa State Univ. in summer 2016 under the Undergraduate Research and Extension Experiential Learning Fellowship. She specifically worked on this SARE project during summer 2016 (3 months).
- We (Rebecca Clay, I, and Co-PIs) published an extension article (CropWatch article) on cover crop grazing and soil compaction.
- We (Rebecca Clay, I, and Co-PIs) presented a poster about on cover crop grazing and soil compaction at the UNL Research Symposium in August 2016. Audience: mostly students and researchers.
- We (Rebecca Clay, I, and Co-PIs) presented a poster at the ASA, CSSA, and SSSA Annual Meetings in Phoenix, AZ. Audience: mostly researchers, crop consultants, and students.
I recruited Philip Hinson, a doctoral student, who will work on this specific project. He will start in spring 2017. His graduate assistantship will be funded through this project. This project is a great opportunity to train both undergraduate and graduate students.