Final report for LNC15-366
This project was successfully completed as planned. The project was conducted on five representative sites including four on-farm sites (Tecumseh, Firth, Mead, and North Platte, NE) and two research sites (Mead and North Platte, NE) across a precipitation gradient in Nebraska. At each site, we had at least three common treatments with three replications. 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 (Firth), 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 most sites followed by oats and mixture of brassicas. Continuous corn as silage (most sites), corn-soybean at the Mead research site, and corn-soybean-wheat at the Tecumseh site were used. We worked with the producers who participated in the establishment of the experiment on their farms and managed cover crops. Each year, we measured subsequent grain yield and cover crop biomass for the cover crop treatments. We also measured soil structural and compaction parameters, water infiltration, and other soil properties. Our data showed no negative effect of grazing cover crops on soil compaction. Grazing and harvesting cover crops had mixed effects on water infiltration. They reduced water infiltration at some sites but not at others. Grazing and harvesting cover crops had no negative effect on soil aggregate stability, soil fertility, soil C concentration, and other chemical properties. Grazing and harvesting effects were highly site-specific (i.e., livestock management). We presented results at several field days. Average attendance of farmers was about 40 at each event. We trained a post doc and several undergraduate student researchers. We have been invited to give several regional and national talks because of the relevance of our project. We also disseminated results in field days and conferences. Overall, the results from this project indicate that cover crop grazing and harvesting have small or no effects on soils and crop yields in rainfed and irrigated systems although high cattle stocking rates may tend to negatively affect soils and crop yields.
We focused on the following objectives:
- Measurement of grain yield, cover crop biomass, and percent soil cover after grazing.
- Assessment of soil structural, compaction, and water infiltration properties as affected by grazing cover crops.
- Assessment of soil fertility properties.
- Economic analysis.
Cover crops may provide supplemental and high quality forage to meet the forage demands for livestock production. While cover crops by definition are not intended to be grazed or harvested, interest is growing in the potential side-benefits of cover crops in integrated crop-livestock systems, especially when forage supply is limited. For example, increased conversion of grasslands to croplands and increased climatic fluctuations in the region have increased pressure on crop residues or silage for animal feed in recent years.
Cattle grazing of cover crops may diversify the emerging integrated crop-livestock production systems. Under proper management (moderate or controlled grazing), cover crops may simultaneously meet both critical goals: soil conservation and provision of feed for livestock. Thus, synergic and successful integration of cover crops with livestock could be an opportunity to improve farm economics while maintaining or improving soil productivity.
While cattle grazing of cover crops appears to be feasible, its implications on soils and yields of subsequent crops have not been, however, widely researched. Some people are concerned that grazing/harvesting cover crops may adversely affect soil processes (i.e., compaction, water infiltration, macroporosity, soil aggregation, C cycling) and concomitantly reduce soil productivity or crop yields. Thus, tradeoffs between using cover crops solely for soil cover and using them for animal feed must be comprehensively studied. This project was specifically designed to address this.
- Cover crop grazing and harvesting would not reduce corn silage and grain yield.
- Cover crop grazing and harvesting would reduce soil structural, compaction, and water infiltration properties.
- Cover crop grazing and harvesting would reduce soil organic matter content and soil fertility.
This project used several experiments of cover crop grazing and harvesting established in representative sites including four on-farm sites and two research sites across a precipitation gradient in Nebraska. The four on-farm sites are located near Johnson, Firth, Mead, 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 all sites in fall 2015 except the on-farm site at Mead, which was established in fall 2016 and the research site at North Platte in fall 2016.
We measured soil properties in spring of each year from 2016 to 2019. 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. Grazing periods and stocking rates varied from site to site. 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 most sites followed by oats and mixture of brassicas. The differences in grazing periods, stocking periods, cover crop species, and crop rotations 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.
We collected soil samples from the 0 to 4 inch and 4 to 8 inch soil depths for the determination of soil properties. Samples were collected after cover crop grazing and before planting main crops, we measured soil structural and compaction parameters, water infiltration, and others at each site using standard methods as discussed in the original proposal. Penetration resistance was measured to assess soil compaction as affected by cover crop grazing and harvesting. Penetration resistance was measured with a static cone penetrometer at 10 points within each treatment plot. Soil cores were collected at the time of water infiltration to determine water content and soil bulk density. Because penetration resistance readings are affected by changes in soil water content, penetration resistance readings were corrected to common water content to eliminate confounding effects of differences in water content. Water infiltration was measured in the field. It was measured at one point within each plot using double ring infiltrometers before planting the primary crops. We also measured wet soil aggregate stability (soil structural quality parameter) by wet sieving soil samples in the laboratory. Soil samples for organic matter and nutrients were also collected. Corn silage and wheat were harvested from two center rows within each plot. The length of the harvested rows were 17.5 ft. Corn for silage was harvested in September and wheat was harvested in July. Samples were processed following standard protocols.
We tabulated data from all sites and years and started work on a manuscript entitled “Integrating cover crops with livestock in irrigated and rainfed systems: Impacts on soil and crops”. This manuscript focuses on crop yields and soils. We are also working on a second manuscript entitled “Economics of cover crop grazing in rainfed and irrigated systems”. We are working with Dr. Jay Parsons (Co-PI) who is helping us out with the economic analysis using measured data on cover crop grazing and harvesting. We will complete the preparation of these two manuscripts in 2020.
Cover crop grazing: Cover crop standing biomass amount
Livestock grazing of CCs, as expected, removed significant amount of CC biomass at both irrigated and rainfed sites. At the irrigated site in 2016, standing biomass between grazed and non-grazed cereal rye CC did not differ due to cattle breaking through the fence and grazing the CC in the non-grazed CC treatment plots for about one day in mid spring. At the irrigated site, CC standing biomass under grazed plots was 7% of the non-grazed CC in 2017 and 8% in 2018. However, at the rainfed site, CC standing biomass under grazed CC plots was 57% of the non-grazed CC in 2016 and 53% in 2018. The larger CC biomass removal by cattle at the irrigated than at the rainfed site is attributed to the higher stocking rate at the irrigated site (16.6 versus 4.6 AUM per hectare).
A comparison of non-grazed CC biomass yield between irrigated and rainfed sites indicates that CC biomass production at the irrigated site was generally greater than at the rainfed site. Averaged across years, non-grazed CC biomass yield at the irrigated site was 2.4 times greater (8.57±3.35 versus 3.63±1.46 Mg ha-1) than at the rainfed site. For example, cereal rye CC yield at the irrigated site was as high as 12.1 Mg ha-1 in 2017. The relatively higher CC biomass production at the irrigated than at the rainfed site is probably due to late termination of CCs, N fertilization of CCs, and one-time irrigation to promote CC establishment at the irrigated site. Cereal rye CC at the irrigated site was drilled in September after corn silage harvest and terminated at corn planting time in late May of each year, while, at the rainfed site, cereal rye was terminated in mid May in 2016. Cover crops were not irrigated nor fertilized at the rainfed site. Our study results suggest that early CC planting, which is particularly feasible in corn silage production systems, combined with fertilization and irrigation offer potential to increase CC biomass production.
Grazing cover crops: Soil compaction
Changes in soil bulk density and penetration resistance were used to evaluate CC grazing impacts on soil compaction. Cover crop grazing had no effect on soil bulk density at either site in any year. However, it had some effects on penetration resistance. At the irrigated site, CC grazing did not affect penetration resistance in the first year but increased it by 40% (1.23 vs. 1.72 MPa) in the 0 to 10 cm soil depth in the second year and by 31% (1.39 vs. 1.82 MPa) in the 10 to 20 cm depth in the third year compared with non-grazed CC and control (no CC). No differences in CC standing biomass between grazed and non-grazed CCs may explain the lack of CC grazing effects on soil compaction in the first year. The increased penetration resistance under CC grazing in spring 2017 and not in spring 2018 for the 0 to 10 cm depth did not appear to be related to differences in precipitation during the grazing months. Grazing when soils are wet can cause more compaction than when soils are relatively dry. Note that mean precipitation in March through May was 187 mm in 2017 and 241 mm in 2018. At the rainfed site, CC grazing did not increase penetration resistance in the first year but reduced it by about 44% in the 0 to 20 cm depth in the third year. At the rainfed site, CCs were not planted in the second year since the winter wheat main crop was planted immediately after soybean harvest in fall as a typical practice in the region.
The increase in soil compaction risks at the irrigated site but not at the rainfed site is most likely due to differences in stocking rate. As described earlier, stocking rate was about 4 times higher at the irrigated (16.6 AUM per hectare) than at the rainfed (4.6 AUM per hectare) site. However, the level of increase in compaction at the irrigated site deserves discussion. While CC grazing increased penetration resistance at the irrigated site, the increase in penetration resistance values were below the threshold levels that can restrict root growth and crop production. Thus, our results after three years of CC management under conservation tillage suggest that while CC grazing at high stocking rates increases soil compaction, such increase can be minimal and may not significantly reduce crop production. Further monitoring of changes in penetration resistance and bulk density across multiple years under different weather conditions is, however, needed to determine how CC grazing affects soil compaction in the long term.
Non-grazed CCs had no effect on bulk density and penetration resistance at any site except at the rainfed site in the third year where it reduced penetration resistance by about 44% in the 0 to 20 cm depth compared to control (no CC). These short-term (three years) results suggest that addition of CC to conservation tillage systems may have positive or no effects on soil compaction.
Grazing cover crops: Soil structure and water infiltration
. Cover crop grazing had no effect on wet aggregate stability expressed as mean weight diameter of water-stable aggregates at any site except at the irrigated site in the second year where it reduced wet aggregate stability by 71% relative to control in the 0 to 10-cm soil depth. At the 10 to 20-cm soil depth, CC grazing reduced wet aggregate stability by 26% compared with non-grazed CC. Based on these results, CC grazing effects water stable aggregation can be variable from year to year. Cover crop grazing effects on cumulative water infiltration measured for three hours were significant in one out of three years at the irrigated site and one out of two years at the rainfed site. At the irrigated site, in the second year, CC grazing reduced the 3-h cumulative infiltration by 80% compared with the average across both non-grazed CC and control. Cumulative water infiltration was numerically the lowest under CC grazed plots at the irrigated site in all years, but due to the high variability in data, CC grazing statistically reduced cumulative water infiltration only in the second year.
At the rainfed site, CC grazing had no effect on water infiltration compared with control in any year unlike at the irrigated site. However, non-grazed CC had a large significant effect on water infiltration in the third year when it increased total cumulative infiltration by 87% compared to both control and grazed CC. At this site, the large effect of non-grazed CC on infiltration in the third year but not in the first year may be due to the use of different CC species in the third year from the first year. Using the CC mixtures that included brassicas or tap-rooted CCs in the third year probably had more positive effects than cereal rye CC in the first year on creating large biopores, which can rapidly increase water infiltration and contribute to precipitation capture. At the irrigated site, the significant and variable effects of CC grazing on water infiltration appear to agree with the study by Franzluebbers and Stuedemann (2008) which reported that CC grazing tended (p = 0.07) to reduce water infiltration rate by about 19% under no-till and conventional tillage cropping systems in Georgia during a 4-yr study. Our results after three years indicate that CC grazing at high stocking rates (16.6 AUM per hectare) can reduce cumulative infiltration in some years.
Harvesting cover crops: Amount of CC biomass
The amount of CC biomass produced at CC harvest in fall was 2.82±0.46 Mg ha-1 in 2014, 1.82±0.22 Mg ha-1 in 2015, and 2.70±0.34 Mg ha-1 in 2016. In 2014, CC biomass produced was 57% oats and 43% brassica. In 2015, biomass produced was 30% grass (oats and cereal rye) and 70% brassica. In 2016, biomass produced was 80% grass (oats and cereal rye), 15% brassica, and 5% pea. In 2014, there was no winter hardy species planted and thus there was no spring CC growth. In 2015, the brassica appeared to outcompete the cereal rye in the unharvested plots, but harvesting resulted in some cereal rye overwintering. The cereal rye biomass prior to termination and subsequent corn planting was 0.60±0.22 Mg ha-1 in the harvested CC in the spring of 2016. The lesser amount of brassica in the fall of 2016 resulted in cereal rye overwintering in both the CC and harvested CC. In early spring prior to termination and corn planting, biomass was 1.04±0.43 Mg ha-1 for non-harvested CCs and 3.0±0.41 Mg ha-1 for harvested CCs,
Harvesting cover crops: Soil compaction, structure, water infiltration
Cover crop harvesting had variable effects on soil properties compared with non-harvested CC and control (no CC) plots. It did not affect soil bulk density and penetration resistance (indicator of soil compaction) except in the third year when it increased penetration resistance from 1.3 to 3.0 MPa in the 0 to 10-cm depth and from 1.5 to 3.6 MPa in the 10- to 20-cm depth compared with non-harvested CC and control (no CC) plots. The increase in penetration resistance with CC harvesting in the third year can be attributed to equipment traffic during CC harvesting.
Cover crop harvesting reduced wet aggregate stability expressed as mean weight diameter of water-stable aggregates compared with non-harvested CC and control (no CC) plots in the second year but had no effect in the third year, which highlights the year-to-year variability in CC harvesting effect on water stable aggregation. However, non-harvested CC significantly and consistently increased wet aggregate stability compared with control plots in both years. It increased wet aggregate stability by 32% in the second year and by 53% in the third year compared with no CCs. The increased wet aggregate stability with non-harvested CC suggest that addition of CC can improve or maintain soil structural attributes under no-till continuous corn silage system, which practically leaves no residue cover after silage harvest. Results also suggest that CCs can increase wet soil aggregate stability and that CC harvesting may or may not eliminate such benefits of CCs for improving soil aggregation.
Similar to the effects on wet aggregate stability, CC harvesting effects on water infiltration was variable from year to year. Cover crop at this CC harvested site increased cumulative water infiltration by 3.5 times in the second year but had no effect in the third year compared with control plots. Compared with non-harvested CC, CC harvesting did not affect cumulative infiltration in the second year but reduced it by 63% in the third year. Non-harvested CC consistently increased water infiltration compared with control in both years. They increased cumulative water infiltration by 4.3 times (from 10.7 to 45.6 cm) in the second year and by 3.8 times (from 7.3 to 27.7 cm) in the third year.
Comparison of harvested and non-harvested CC effects on soil properties indicates that CC harvesting may or may not eliminate the soil benefits of CCs. Results further suggest that CC harvesting can provide additional feed to livestock but their effects on soil properties may be similar to not having CCs in some years under the conditions of this study.
Cover crop grazing and harvesting: Impacts on soil fertility and crop yield
Cover crop grazing had no significant effect on soil fertility parameters including pH, and concentration of organic matter, nitrates, exchangeable K, and available phosphates. However, nitrate concentration was higherunder non-grazed CC compared with grazed CC and control in the 0 to 10 cm depth at the rainfed site. Cover crop harvesting had some effects on soil fertility properties. It is important to reiterate that CC was harvested in October and the soil was sampled in mid-spring. Cover crop harvesting reduced soil nitrate concentration by 37% in the 0 to 10 cm soil depth compared with no CC, suggesting that CC harvesting may capture N and reduce leaching although differences in soil nitrate concentration between non-harvested CC and no CC were not significant. Non-harvested CC increased concentration of organic matter by 7% compared with the average across harvested CC and control in the 0 to 10 cm soil depth. The increased soil organic matter concentration under non-harvested CC at this site after three years could be due to the return of the aboveground biomass of CC. Note that non-harvested CCs at this study site produced relatively larger amount of biomass (2.8 in 2014, 1.8 in 2015, and 2.7 Mg ha-1 in 2016) compared with other studies in the region where CC biomass production is often < 1 Mg ha-1, which generally had no significant effects on soil properties including soil organic matter concentration.
Cover crop grazing did not significantly affect crop yields at any site. However, at the irrigated site, while not statistically significant, corn silage yield after grazed CC tended to be consistently lower than control (no CC) in all years. It also tended to be lower in the first and second year compared with non-grazed CC. The trend for decreased crop yields at the irrigated site but not at the rainfed site is probably due to the higher stocking rates (16.6 versus 4.6 AUM per hectare), which increased penetration resistance and reduced water infiltration. particularly in the second year, s at the irrigated site. Results from the irrigated site suggest that while the CC grazing-induced increase in soil compaction did not significantly reduce crop yields, it possibly caused some reduction in root growth, which may explain the trend for reduced crop yields at this site. Additional monitoring is needed to determine how CC grazing at high stocking rates affects crop yields in the long term (> three years). Note that in our study, animals grazed CCs for about two months only, which can have a different effect on soil compaction and other soil and crop parameters from intensive or continuous grazing, which is not uncommon in the study region. For example, a question that needs to be answered is that whether moving cattle more frequently such as daily or weekly from field to field to reduce soil exposure to grazing impacts would be a better alternative.
The absence of statistically significant CC grazing effects on yields is most probably due to the variable effects of grazing on soil properties such as compaction. Had CC grazing increased soil compaction above threshold levels that restrict root growth and reduced soil fertility such as organic matter concentration, it may have significantly reduced crop yields. Even under high stocking rates (16.6 AUM per hectare) at the irrigated site, CC grazing had no significant negative effect on crop yields. Some concerns exist among producers that CC grazing may compact and reduce subsequent crop yields, but our results from both sites (irrigated and rainfed) suggest that moderate grazing of CC does not affect crop yields while high stocking rate may tend to reduce crop yields.
Similar to the effects of CC grazing, harvesting of CCs had mixed effects on crop yields at the Firth site. It reduced corn silage yields in the second year relative to CC and control treatments, but had no effect in the first and third year. In the second year, harvesting CCs reduced corn silage yield by 69% (16.55 versus 9.75 Mg ha-1). The significant decrease in corn yield in one year and not in the other is somewhat surprising but it may be attributed to the year-to-year variability although the underlying mechanisms deserve further investigation.
Results from this 3-yr study in rainfed and irrigated conservation tillage cropping systems in the western Corn Belt suggest that livestock grazing of CCs may have small or no effects on soil properties and crop production, depending primarily on the cattle stocking rates. Cover crop grazing at high stocking rates (16.6 AUM per hectare) compacted the soil and reduced water infiltration in one of three years, but the increase in the compaction level was below the threshold levels that can significantly restrict root growth. Grazing of CC had no effect on wet soil aggregate stability and concentrations of organic matter and essential nutrients, suggesting that CC grazing may not adversely affect soil structural and fertility properties in the short term. Also, CC grazing did not significantly affect crop yields although it tended to reduce yields at the irrigated site. The trend for reduced corn silage yields at the irrigated than at the rainfed site may be due to the increased soil compaction as a result of higher stocking rate at the irrigated (16.6 AUM ha-1) than at the rainfed (4.6 AUM ha-1) site. Cover crop harvesting in fall had inconsistent effects on soils and crop yields measured the following year. Our results also indicated that both non-grazed and harvested CCs improved soil properties in some years but had no effects on crop yields. Use of brassicas mixed with grass CC appears to improve soil properties such as water infiltration more than grass CCs alone in the short term. Results suggest that the early response (<three years) to CC grazing can be highly site-specific, depending on stocking rate, cropping systems, and CC species, among others. Based on our results, integrating CCs with livestock production can be a potential alternative in the study region, but stocking rate should be considered. High stocking rates (16.6 AUM ha-1) can have some adverse effects on soil and crop yields relative to low stocking rates (4.6 AUM ha-1). Additional studies are needed to determine how livestock grazing at different stocking rates of CCs affect soils and crop yields in the long term and establish the threshold levels of CC grazing. Overall, CC grazing at moderate stocking rates (i.e., 4.6 AUM ha-1) and harvesting under conservation tillage cropping systems can generally have no effects on soil properties and crop yields in the short term although high stocking rates (i.e., 16.6 AUM ha-1) could increase risks of soil compaction, potentially reducing crop yields.
The project results impacted the knowledge of people through dissemination of information detailed below. While it is hard to document the specific impacts on farmer’s behavior, the results from this project will have a larger impact in coming years. We collected research data to show effects of grazing. We have received many positive comments on this regional project. Farmers have always expressed interest in research data to influence their management decisions.
- We gave talks to 40 to 50 farmers in each site at least once during the duration of the project.
- We trained at least 9 undergraduate students in research using this timely project.
- Trained a postdoctoral researcher in the economic analysis of cover crop grazing. The post doc is writing the paper on cover crop grazing and economics.
- I was invited to speak at two Symposiums. One, the International Annual Meetings, ASA, CSSA and SSSA, Tampa, FL,. The topic of my talk: “Does Grazing or Harvesting of Cover Crops Affect Soils and Crop Production? Assessment in Different Soil Types and Management Scenarios”. 2017. Two, International Annual Meetings, ASA and CSSA, Baltimore, MD. The topic of my talk: “Soil Health and Cover Crops” November, 2018.
- We published an extension article about grazing cover crops (https://cropwatch.unl.edu/2019/cover-crop-grazing-impacts-soils-and-crop-yields)
- Two journal articles are under preparation after 3 years of the project.
Educational & Outreach Activities
Toured the experiments during field days. Farmers asked questions and participated in discussions on cover crop grazing.
Showed cover crop experiments to farmers and extension specialists. Shared research findings with them through oral presentations.
- Soil health and cover crop grazing
Changes in knowledge are expected through field days hosted and conferences
Just as an example, Dan Rice from Prairieland Dairy near Firth, NE has noted that harvesting cover crops for dairy cows has supplemented high quality feed. Mixed cover crops produced higher quality forage than grass cover crops (rye). He has been successful with cover crops. Based on our data, he is happy to see that harvesting cover crops does not negatively affect soil properties and crop yields.