Final report for OS20-133
Interest in cover cropping is growing rapidly among row-crop farmers in the Southeast. However, the long cash-crop growing seasons in the Southeast limit the window for successful establishment of fall cover crops. Inter-seeding summer cover crops alongside cash crops could potentially address this challenge. The environmental and economic benefits of an inter-seeded cover crop depend upon cover crop selection and management practices. The objective of this project was to evaluate inter-seeded white clover, buckwheat, pigeon pea, and their mixture on three different planting dates (V4, V7, and V10 growth stages of corn) for their effect on improving soil moisture, enhancing soil health, and impacting silage corn biomass yield. The study was conducted in collaboration with a farmer at Mull Meadow farms in Anderson, SC in 2020 and 2021. We found that cover crops when inter-seeded at V7 or V10 saved more water in the 20 cm soil profile than when they inter-seeded at V4 or compared to no cover crop control. Cover crops when inter-seeded at V10 or V7 growth stages of corn increased the biomass production of corn compared to the no-cover crop control. However, this benefit was not realized when cover crops were inter-seeded at V4 growth stage of corn. Soil health score was higher when cover crops were planted at V7 and V10 corn growth stages compared to V4 and no-cover crop control in both seasons. The results indicate that with careful selection of species and appropriate planting time, inter-seeded cover crops can save water in the soil profile. In addition, V7-V10 appear to be the ideal planting time for cover crop inter-seeding in corn based on soil water conservation, soil health, and corn biomass production.
Evaluate inter-seeded white clover, buckwheat, pigeon pea, and their mixture on three different planting dates (V4, V7, and V10 growth stages of corn) for their effect on improving soil moisture, enhancing soil health, and impacting silage corn biomass yield.
- - Producer
The field trials were conducted in 2020 and 2021 on the farmer cooperator’s farm (Mull Meadow Farms, Anderson County, SC). The on-farm trial evaluated the effect of inter-seeded cover crops with corn on soil health, soil moisture content, weed suppression, and corn performance.
A forage corn variety, pioneer 2089VYHR was planted at a rate of 36,000 plants/acre in 2020 and 32,000 plants/acre in 2021 using a John Deere Vab Brunt planter. Row spacing was 36 inches. The cover crop treatments included white clover, buckwheat, pigeon pea, and their mixture. The cover crop treatments were sown manually using a push spreader at V4, V7, and V10 corn growth stages. Seeding rates were 3 lb/acre for white clover, 48 lb/acre for buckwheat, and 10 lb/acre for pigeon pea as single species (Clark, 2012) and 1, 16, and 3.3 lb/acre for white clover, buckwheat, and pigeon pea, respectively in the mixture (Wortman et al., 2012). The control treatment was forage corn planted without any inter-seeded cover crops. All plots were 18 feet x 18 feet size. Plots were maintained as rain-fed. Corn was harvested using a New Holland forage harvester (BR7060, Racine, WI 53404, USA) and baled to make haylage. Cover crops were baled along with corn.
Experimental design for the field trial was a split-plot with planting time (or corn growth stage) as the main-plot factor and cover crop treatments as the sub-plot factor. There were 4 replications for each treatment combinations. Analysis of variance was performed using the GLIMMIX procedure in SAS.
Soil health was assessed at corn harvest using the Haney test at the Ward Laboratories, Inc, Kearney, NE, which is an integrated approach to soil testing using chemical and biological soil test data. The Haney test at the Ward Laboratories involves a dual extraction procedure that determines pH, soluble salts, organic matter, soil respiration; H2O Extract: total nitrogen, total organic carbon, total organic nitrogen; H3A Extract: nitrate-nitrogen, ammonium-nitrogen, inorganic nitrogen, total phosphorus, inorganic phosphorus, organic phosphorus, potassium, calcium, magnesium. To conduct the Haney test, soil samples were collected from each plot at the time of corn harvest and submitted to the Ward Laboratories, Inc, Kearney, NE.
Soil water content was measured using a Hydrosense II CS658 soil moisture probe (Campbell Scientific Devices). Soil water content was measured at 80, 111, 136 days after corn planting. Measurements were taken at 20 cm (7.87 inches) depths.
Weed biomass was estimated by randomly placing a quadrat with an area of 0.25 m2 in every plot, cutting all weed biomass from the 0.25 m2 area, and drying that to estimate dry weight.
Corn biomass was hand-harvested from 1 m length of rows at harvest from each plot (single row per plot), to determine dry weight. Biomass was measured at harvest maturity when corn was at R5-R6 growth stage.
Figure 1 shows rainfall and temperature data during the growing seasons in 2020 (season-1) and 2021 (season-2) in relation to 30-year climate normals. Season-2 started as a drier year compared to season-1. However, toward the end, season-2 received higher rainfall than season-1. For example, in the last 14 days, rainfall was 6 and 11 cm in season-1 and 2, respectively. Average daily temperatures for both seasons were more or less similar.
Figure 1. Cumulative precipitation (a) and daily average temperatures (b) during the study perods in 2020 and 2021 in comparison with the 30 year normal data. Cumulative precipitation normals for both seasons were calculated from the daily precipitation normal for a period of 30 years from 1991 to 2020. Precipitation and temperature data were obtained from the South Carolina State Climatology Office, a division within the South Carolina Department of Natural Resources
In both seasons, the ‘planting time-by-cover crop interaction’ effect was not significant on volumetric water content, but the main effect of planting time was significant on volumetric water content (Table 1). In season-1, cover crops when inter-seeded at V7 or V10 saved more water in the soil profile than when they inter-seeded at V4 or compared to control (no-cover) (Figure 2). In season-2, high rainfall in the last two weeks before the measurement date prevented to observe differences in soil moisture content among treatments. Still, soil moisture contents were generally higher under inter-seeded conditions than control. These results suggest that the concern of inter-seeded cover crops depleting soil water in the system would not be true if we are careful in selecting the right species of cover crops and the right timing for inter-seeding.
Table 1: Analysis of variance results demonstrating the effect of inter-seeded cover crops on volumetric water content.
Figure 2. Effect of inter-seeded cover crops on volumetric soil water content
We also studied the effect of inter-seeded cover crops on soil health and assessed the soil health scores under different treatments. Soil health score is a combination of soil respiration, carbon to nitrogen ratio, total organic carbon and total organic nitrogen. It is a score attributed by the Ward lab to represent the level of health of the soil. The ‘planting time-by-cover crop interaction’ effect was not significant on soil health score, but the main effect of planting time was significant on soil health score (Table 2). In both seasons, the soil health score was higher when cover crops were planted at V7 and V10 corn growth stages compared to V4 and no cover crop control (Figure 3).
Table 2: Analysis of variance results demonstrating the effect of inter-seeded cover crops on soil health score.
Figure 3. Effect of inter-seeded cover crops on soil health score
In both seasons, the ‘planting time-by-cover crop interaction’ effect was not significant on silage corn biomass production as well, but the main effect of planting time on corn biomass production was significant (Table 3). In season-1, cover crops when inter-seeded at V10 or V7 growth stages of corn increased the silage biomass production of corn compared to the no-cover crop control (Figure 4). However, this benefit was not realized when cover crops were inter-seeded at V4 growth stage of corn. This might be because of the increased level of complementarity between cover crops and corn when planted at or later than V7 growth stage of corn. Biomass in season-2 was lower than that in season-1. This might be because we used a higher seeding rate in season-1 and that combined with the dryness in the beginning of the season resulted in a poor stand establishment (Figure 5). In season-2, silage corn biomass production was greater when cover crops were inter-seeded at V7 growth stage of corn, but the corn biomass production when cover crops were inter-seeded at V10 was lower than that of control (Figure 4). We suspect that the reason was a planting error in season-2 with sunflower seeds mixing with the corn seeds in the V10 section.
Table 3: Analysis of variance results demonstrating the effect of inter-seeded cover crops on silage corn biomass.
Figure 4. Effect of inter-seeded cover crops on silage corn biomass
Figure 5. Corn stand establishment in both seasons.
- With careful selection of species and appropriate planting time, inter-seeded cover crops are able to save water in the soil profile
- Inter-seeded cover crops can improve soil health and cash crop yields if sown at the appropriate time
- V7-V10 appear to be the ideal planting time for cover crop interseeding in corn based on soil water conservation, soil health, and corn biomass production
Educational & Outreach Activities
Three presentations were made by the graduate student based on the results. One was in the American Society of Agronomy Annual meeting, another in the American Society of Agronomy's Southern branch annual meeting, and the third one at Clemson University. The audience included researchers, students, educators, and farmers. The graduate student received first prize for the presentation at the American Society of Agronomy Annual meeting (national level), which demonstrates the importance and impact of the study. In addition, we communicated the results to farmers at field days and producer meetings. The project results were incorporated into multiple courses (Principles of Field Crop Production and Major World Crops) that the PI is teaching at Clemson.
Lack of diversity in the production system that makes it less adaptable to extreme climatic events and deterioration of soil health that affects long-term sustainability of the system are major challenges for organic and conventional farmers (NORA, 2016; personal communication with farmers). In order to address the above challenges, crop production needs methods that make the system more diverse, protect the environment, and are sustainable in the long run, which makes cover cropping a suitable approach to address those challenges. However, farmers may be reluctant to adopt the system without seeing it in action. This project is the first step in determining the feasibility of inter-seeded cover crops in corn production systems and optimizing this technique in the upstate of South Carolina. This approach, if implemented properly, will increase soil organic matter content, enhance soil health, improve soil moisture content, and suppress weed growth to benefit the companion cash crop. We anticipate that the project will help increase the adoption of this relatively new technique (cover crop inter-seeding) by row crop producers, reduced use of irrigation water, herbicides, and fertilizers, and development of soil organic matter leading to healthier soils. If this technique leads to reduced irrigation, herbicide, and fertilizer costs, it will indeed improve the economic feasibility and sustainability of cover cropping practices.