Legume-based cover crops, when inter-seeded, can lead to economic and environmental efficiency because of nutrient supply, reduced herbicide use, and control of soil erosion and nutrient leaching (Sanders et al., 2017). White clover may be a good option because it can be as effective as herbicides to control weed (Hartwig and Ammon, 2002). White clover also encourages the association between mycorrhizal fungi and corn plants to assist in nutrient supply from soils with high phosphorous fixation capabilities (Deguchi et al., 2007).
Buckwheat is another cover crop that has been shown to work well as an inter-seeded cover crop with corn (Loran Steinlage- row crop farmer, Presentation at the Conference on Building Soil Health: Principles, Practices and Profitability, Clemson, SC, 10/28/2019). Its benefits include rapid establishment and land cover, strong weed suppression, phosphorous scavenging, and ability to thrive in low fertility soils and attract beneficial insects (Clark, 2012). It produces abundant fine roots, which makes soil friable (Clark, 2012). This in turn makes this species a good choice for compacted soils in the Southeast.
Daikon radish is a warm season broadleaf Brassica cover crop grown in the South. A major benefit of radish is its ability to perform “biological tillage” by growing a large taproot that can greatly disturb soil in the E-horizon (Williams and Well, 2004; Chen and Well, 2010). Radish decomposes quickly in the spring, leaving large holes in the soil. This can be beneficial for no-till farmers or for those who are interested in reducing spring tillage. The taproot can penetrate through compacted soil and alleviate compaction (Marshall et al., 2016).
For the success of an inter-seeded system, the cover crop planting time is critical as cover crops themselves can act as weeds. This happens primarily if cover crops establish during the critical weed-free period of the cash crop. Research suggests that early cover crop planting dates that align with the V5 to V7 corn growth stage have negligible impacts on corn yield (Minnesota Extension, PennState Extension). Targeting the V7 corn growth stage can position the cover crop establishment after the critical weed-free period in corn. More research is needed to determine how early cover crops can be inter-seeded into corn without impacting yield.
The proposed research will evaluate inter-seeded white clover, buckwheat, Daikon radish, and their mixture (to test any complimentary interactions these functionally distinct species may offer) on three different planting dates (V4, V7, and V10 growth stages of corn) for their effect on building soil organic matter, enhancing soil health, improving soil moisture, and suppressing weed growth. Forage corn is selected as the cash crop primarily because the farmer cooperator grows row crops to make haylage for his cattle, and corn is the crop of his choice. The effect of inter-seeded cover crops on corn yield will be assessed. An economic analysis will be conducted to evaluate the direct (monetary) and environmental benefits, costs, and risks of inter-seeded cover crops. We will also develop and implement outreach programs to communicate the results with farmers and stakeholders.
The proposed project will involve the farmer cooperator in each step of the planning and implementation processes, and the study will be conducted on his farm (Mull Meadow Farms, Anderson County, SC). The on-farm trials will be conducted in the summer of 2020 and 2021 to evaluate the effect of inter-seeded cover crops with corn on soil health, soil moisture content, weed suppression, and corn performance.
The trial will involve no-till operation, which is the standard practice for the farmer cooperator. Prior to planting, a low-residual herbicidal application will be carried out to control weeds, and fertilizer application will be conducted as per soil test recommendations. A forage corn variety will be planted at a desired rate of ~30,000 plants/acre (recommended corn population for inter-seeding: PennState Extension; also the desired rate by the farmer cooperator) and with 36 inches row spacing using a Bushhog Lilliston 9690 no-till planter. The cover crop treatments include white clover, buckwheat, Daikon radish, and their mixture (species may change if further research necessitates). The cover crop treatments will be sown using an inter-seeder at V4, V7, and V10 corn growth stages. Seeding rate will be approximately 3 lb/acre for white clover, 48 lb/acre for buckwheat, and 8 lb/acre for Daikon radish as single species (Clark, 2012) and 1, 16, and 2.7 lb/acre for white clover, buckwheat, and Daikon radish, respectively in the mixture (Wortman et al., 2012). The control treatment will be forage corn planted without any inter-seeded cover crops. Weeds will be suppressed in the ‘control plots’ through herbicide application, whenever necessary. All plots will be 20 feet x 20 feet size. Irrigation will be provided whenever necessary. Corn will be harvested using a New Holland forage harvester and baled to make haylage. Cover crops will be winter-killed (and sprayed/chopped, if necessary).
Experimental design for the field trial will be a randomized complete block with 5 replications. Analysis of variance will be performed using the GLIMMIX procedure in SAS.
Soil health will be 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. The total organic carbon and total organic nitrogen values will be used to determine the C:N ratio. The soil respiration estimates will be related with microbial biomass and potentially mineralizable nitrogen. To conduct the Haney test, soil samples will be collected from each plot at the time of corn harvest and submitted to the Ward Laboratories, Inc, Kearney, NE. The cation exchange capacity (CEC) will be estimated through a standard soil test at Clemson Agricultural Service Laboratory. The standard soil test will also estimate nutrients, which are not tested through the Haney test such as zinc, manganese, copper, boron, and sodium.
Soil water content will be measured using a soil moisture probe (Delta T Devices PR2 soil moisture profile probe). The PR2 access tubes will be installed in field plots after corn emergence. Soil water content will be measured at three-weeks intervals throughout the corn growing season. Measurements will be taken at 10, 20, 30, 40, 60, and 100 cm (39 inch) depths.
Percent weed cover will be estimated through the point intercept method to assess weed presence in field plots (Elzinga et al., 2001). Briefly, weed cover is measured by point intercept based on the number of “hits” on the weed species out of the total number of points measured along a transect line, and expressed as a %. The measurement will be conducted at three-weeks intervals throughout the corn growing season.
Cover crop biomass will be hand harvested from 1 m2 area within each plot at the time of corn harvest, to determine dry weight.
Corn performance: Corn plant height and canopy light interception (using a line quantum sensor) will be estimated at three-weeks intervals throughout the season. Corn biomass will be hand harvested from 1 m length of rows at harvest from each plot (single row per plot), to determine dry weight.
Cost-benefit analysis will be conducted to compare different cover cropping practices (none, single species, and multi species cover crops), with the aim of evaluating monetary gains and losses to producers and associated ecosystem services. On-farm costs include the costs of seeds, planting operations, maintenance, and residue management (if any). The on-farm benefits include increased corn biomass yield and savings on irrigation, fertilizer, and other chemical inputs (Griffin and Hesterman, 1991; Vyn et al., 1999; Labarta et al., 2002; Adusumilli and Fromme., 2016). The off-farm analysis will quantify changes in soil characteristics that could affect off-farm surface and ground water quality (nutrient and sediment loads), wildlife habitat, and other ecosystem services (Snapp et al., 2005; Schipanski et al., 2014). In the analysis, all cash gains and losses over the entire period of the project will be discounted to one time period (i.e., the Net-Present Value approach), including cash flows resulting from all potential risks involved in this project.
Experience of the PI in working with farmers
Dr. Narayanan (PI) has pursued two previous SSARE on-farm grants (OS16-096 and OS18-118) for cover crop projects and worked with farmer cooperators in the last four years. Projects OS16-096 and OS18-118 compared the effects of single species and multi-species winter cover crops on soil moisture and soil health in comparison to a fallow (These two projects are not related to inter-seeded cover crops, i.e. the proposed project). As part of the projects OS16-096 and OS18-118, Dr. Narayanan has worked with farmers for conducting on-farm trials, training programs, and presenting and demonstrating research results in field days. She is part of the Clemson Sustainable Agriculture Program and member of the Clemson Organic Farm committee, and she regularly works with farmers in these roles.
- - Producer
We finished the first field season of the trial in the Summer of 2020. The study was conducted 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 30,000 plants/acre and with 36 inches row spacing using a John Deere Vab Brunt planter. 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 147 DAP (days after planting of corn) on 11 September 2020, which was 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 performance: Corn plant height (at 71 and 136 DAP) and leaf area index (using LAI 2200, LI-Cor) (77 DAP) were estimated. Corn biomass was hand harvested from 1 m length of rows at harvest from each plot (single row per plot), to determine dry weight.
A cost-benefit analysis is underway to compare different cover cropping practices (none, single species, and multi species cover crops), with the aim of evaluating monetary gains and losses to producers and associated ecosystem services.
Single species of white clover and the mixture of white clover, buck wheat, and pigeon pea appeared to save water in the 20 cm profile when planted at V10 corn stage compare to no cover crop control or other cover crops planted at V4 and V7 growth stages of corn (Figure 1). This implies that V4 and V7 might be too early to inter-seed cover crops in corn when we consider soil water savings.
Figure 1. Effect of inter-seeded cover crops on volumetric soil water content
The ‘planting time-by-cover crop interaction’ effect was not significant on any of the soil health indicators we measured. So, we looked at the main effect of planting time on soil health. Soil respiration measures how much life the soil contains. The more CO2 a soil produces, the higher is the microbial biomass. In our study, soil respiration was higher when cover crops were planted at V7 and V10 corn growth stages compared to V4 and no cover crop control (Figure 2a). Organic nitrogen release is the overall notrogen credit given to the soil based on CN ratio, soil respiration, and the pool of organic nitrogen. The higher the Organic nitrogen release potential, the more nitrogen will be available for the microbes to access. In our study, the organic nitrogen release was higher when cover crops were planted at V7 and V10 corn growth stages compared to V4 and no cover crop control (Figure 2b). 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. In our study, 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 2. Effect of inter-seeded cover crops on soil health indicators
The ‘planting time-by-cover crop interaction’ effect was not significant on silage corn biomass production as well. So, we looked at the main effect of planting time on corn biomass. Cover crops when inter-seeded at V10 growth stage of corn increased the silage biomass production of corn compared to the no-cover crop control (Figure 3). However, this benefit was not realized when cover crop was inter-seeded at V4 and V7 growth stage of corn. This might be because of the increased level of complementarity between cover crops and corn when planted at V10 growth stage of corn.
In conclusion, based on the data from the 1st field season, the V10 corn growth stage appears to be the ideal planting time for cover crop inter-seeding in corn based on soil water conservation, soil health, and corn biomass production. The results will be verified in the 2021 field season.
Educational & Outreach Activities
Two presentations were made by the graduate student based on the results. One was in the American Society of Agronomy’s Southern branch annual meeting. The other was at Clemson University. Audience included researchers, students, educators, and farmers.
The conventional row crop producers rely primarily on herbicides for weed control. On the other hand, organic row crop producers rely primarily on cultural and mechanical practices to manage weeds, and consider weed control among their greatest production costs. Growing numbers of row crop producers are adopting sustainable practices in response to increased demands from both organic livestock producers and final consumers. This is evident from expansion of certified organic cropland by nearly 80%, to 3.1 million acres between 2005 and 2011 in the US. Thus, development of more effective non-chemical weed management strategies can have substantial positive economic and environmental impacts, as far as conventional and organic row crop production are considered. The use of cover crops offers a more sustainable, system-based approach to weed management than herbicides and tillage.
Apart from weed infestation, other major challenges for organic and conventional farmers are 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 (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. The proposed 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. Our economic analysis to compare the cost and benefit of this approach will address a major roadblock to producer adoption of cover crop inter-seeding technique. We anticipate that the project will result in greater 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.