Reducing weed pressure on crops without affecting soil health through intense and frequent tillage and cultivation practices is a major challenge in sustainable crop production. In recent years, cover crops are gaining importance as a sustainable practice that improves cropping system intensity and diversity as well as improving soil health and reducing weed pressure. However, few grain producers in the Southeast have included cover crops as part of their cropping systems because of several concerns. A major one being the possibility that cover crops may reduce the amount of water stored in the soil profile for the next grain crop, potentially reducing yields.
The objective of this study is to evaluate the common cover crops including grasses, legumes, and brassicas as single species or in mixtures and compare them with two control treatments: fallow with and without herbicide control in an on-farm trial.
Soil water content will be measured at 10, 20, 30, 40, 60 and 100 cm depths at biweekly intervals starting from cover crop establishment until one month after planting of next cash crop (soybean). Biomass will be measured at monthly intervals throughout the cover crop season. Cover crop water use efficiency will be estimated as the amount of dry biomass produced per unit of water used during the growing period. The study will provide information to develop grower recommendations on cover cropping to optimize biomass and soil moisture for subsequent crops.
Objective 1: Evaluate the common fall cover crops in SC for soil moisture retention, biomass production, and water use efficiency.
On-farm trials will be conducted in the Millam farm (Anderson County, SC) during 2018-2019 and 2019-2020. The treatments will be;
- Mixture of five (Austrian winter peas, rye, wheat, crimson clover, hairy vetch, and oats), legume-grass combination, source-Adams Brisco Seed Company
- Mixture of five (oats, wheat, crimson clover, radish, and turnip), legume-brassica-grass combination, NRCS recommendation
- Mixture of two (crimson clover and rye), legume-grass combination, source-Adams Brisco Seed Company
- Mixture of two (oat and radish), grass-brassica combination, source-Adams Brisco Seed Company
- Mixture of two (crimson clover and turnip), legume-brassica combination, SARE recommendation
- Single species of legume (crimson clover), source-Adams Brisco Seed Company
- Single species of grass (rye), source-Adams Brisco Seed Company
- Control 1 – Fallow with herbicide control
- Control 2 – Fallow without herbicide control
Treatment selection criteria
One of the criteria for choosing the multispecies cover crop treatments-1&2 was combination of three functional groups (grass, legume, and/or brassica). In addition, we like to compare an available cover crop mix (Treatment 1, Adams Brisco Seed Company) with an NRCS recommendation (Treatment 2). Treatments 3-5 are duplex combinations of grass, legume, and brassica. We chose the commonly available fall cover crop species in the region to design treatments 3-7. Treatments 8&9 are common fallow-practices adopted by producers in SC.
Cover crop culture
A pre-plant operation with a disc harrow would be conducted to prepare the seedbed. Nutrient status of the land will be determined through a soil test and fertilizer will be applied accordingly prior to planting of cover crops. Cover crops will be planted in October in both trials (2018 and 2019). Each cover crop treatment and replicate will be planted using a seed drill in plots of 6 m (20 feet) by 6 m. Seeding rates will be based on recommendations of the seed company (Adams Brisco), NRCS, and SARE (SARE, 2012). Cover crops will be terminated prior to flowering or one month prior to planting of the following cash crop (whichever happens first) in order to prevent seed production and the potential to become a future weed. Soybean will be planted using a no-till planter one month after cover crop termination. No herbicides, fertilizers, and irrigation will be provided to the soybean crop. We chose soybean as the subsequent crop as it was preferred by our farmer cooperator.
Soil water content will be measured at biweekly intervals using a soil moisture probe (Delta T Devices PR2 soil moisture profile probe). The PR2 Probe access tubes will be installed after cover crop emergence and will be placed in the center of each plot in areas most representative of cover crop growth. Soil water content will be measured biweekly starting from cover crop establishment (~3 weeks after planting) until one month after planting of next cash crop (soybean). Measurements will be taken at 10, 20, 30, 40, 60, and 100 cm (39 inch) depths. A rain gauge will be installed in the field to measure daily precipitation. Cover crop water use (cover crop evapotranspiration) for a given plot between two sampling dates will be calculated as ‘change in soil water content between the sampling dates + precipitation – run off – drainage’ (Zhang et al., 2001). Cumulative water use will be calculated as the sum of biweekly crop water use during the cover crop growth period. Soil water depletion by cover crop treatments will be compared with that of control treatments to determine the loss of stored soil water due to cover cropping. If soil water content after cover crop termination is greater in any plot, compared to fallow, that cover crop treatment would be a candidate for a sustainable practice for this region to reduce weed pressure and improve soil health without depleting stored soil water.
Just before cover crop termination, biomass will be hand harvested from 1 m2 area within each plot to determine dry weight (Creamer and Baldwin, 2000; Kuykendall, 2015). Cover crop water use efficiency will be estimated as the amount of dry biomass produced per unit of water used during the growing period. Identification of high water use efficient cover crops (single species/mixes) would help identify cover crops that produce large amount of biomass, use less amount of water or a combination of both.
Experimental design will be a randomized complete block with five replications. Analysis of variance will be performed using the MIXED procedure in SAS to determine effect of cover crops. Cover crop treatments will be considered as fixed effects and replications as random effects.
An on-farm workshop, presentations at field days and professional meetings, and publications (a peer-reviewed journal article and an extension article) will disseminate results to farmers and other stakeholders, researchers, and students and help producers understand the benefits of including water-use-efficient cover crops in sustainable grain crop production systems.
Due to the unavailability of the farmer cooperator (which was due to an unexpected medical condition) and unfavorable weather conditions, our planting of cover crops got delayed until 6 December 2019. Still we got adequate seedling emergence in our field plots. But, unfortunately, winter weather was abnormal in our region, and the emerged seedlings were subsequently killed by hard freezes without snow protection. We consulted with regional cover crop experts like Mark Schonbeck, extension agents, and the project team, and decided to wait until mid May to see whether the plants will recuperate, but it did not happen. So we replanted on 11 March 2019. Currently, the seedlings are emerging, and we hope to get adequate stand in a few weeks to start the measurements.
We installed access tubes for soil moisture measurements in all plots. The project team involving the PI, Co-PI, student, farmer cooperator, and an extension agent is meeting regularly to discuss the progress and gather suggestions.
Educational & Outreach Activities
An on-farm workshop, presentations at field days and professional meetings (conducted in the second year), and publications (a peer-reviewed journal article and/or an extension article submitted shortly after the completion of the study) will disseminate results to farmers and other stakeholders, researchers, and students and help producers understand the benefits of including water-use-efficient cover crops in sustainable grain crop production systems.