Final report for GS18-192
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 was to evaluate the common fall cover crops in SC for soil moisture retention, biomass production, and water use efficiency. Soil water content was measured at 10, 20, 30, 40, and 60 cm depths at biweekly intervals starting from cover crop establishment. Biomass was measured at monthly intervals throughout the cover crop season. Cover crop water use efficiency was estimated as the amount of dry biomass produced per unit of water used during the growing period. Mixture of 5a, rye, and the mixture of rye and crimson clover produced the highest amounts of biomass in both seasons. These cover crops did not deplete soil moisture than did other cover crops or the fallow control in both seasons. The same cover crops also had the highest values for water use efficiency in both years. Water use efficiency is the ratio between biomass and water use. Since mixture of 5a, mixture of rye and crimson clover, and rye did not utilize more water than other crops, their higher water use efficiency is a result of higher biomass. The study provides 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.
Two field trials were conducted during Fall-winter of 2019-2020 and 2020-2021. The treatments were;
- Mixture of five-a (Austrian winter peas, rye, wheat, crimson clover, hairy vetch, and oats), legume-grass combination, source-Adams Brisco Seed Company
- Mixture of five-b (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
Soil water content was measured at biweekly intervals using a soil moisture probe (Delta T Devices PR2 soil moisture profile probe). The PR2 Probe access tubes were installed after cover crop emergence and were placed near the center of each plot in areas most representative of cover crop growth. Soil water content was measured at 90, 111, 143, and 165 days after planting (DAP) of cover crops during the cover crop season and 233, 260, 279, 316, and 385 DAP during the soybean season in field season-1. In field season-2, soil water content was measured at 112, 143, and 154 days after planting (DAP) of cover crops during the cover crop season and 305 DAP during the soybean season. Measurements were taken at 10, 20, 30, 40, and 60, cm depths. Cover crop water use (cover crop evapotranspiration) for a given plot between two sampling dates was calculated as ‘change in soil water content between the sampling dates + precipitation. Cumulative water use was calculated as the sum of biweekly crop water use during the cover crop growth period. Soil water depletion by cover crop treatments was compared with that of control treatments to determine the loss of stored soil water due to cover cropping.
Cover crop biomass was measured at 115, 144, and 170 DAP in field season-1 and 111, 143, and 159 DAP in field season-2. Cover crop water use efficiency was estimated as the amount of dry biomass produced per unit of water used.
Experimental design was a randomized complete block with five replications. Analysis of variance was performed using the GLIMMIX procedure in SAS. Cover crop treatments were considered as fixed effects and replications as random effects.
During cover crop season, no cover crops depleted soil moisture than the fallow control until termination in field season-1 &2 (Figures 1&2). At termination, crimson clover and the mixture of rye and crimson clover retained less soil moisture compared to the fallow control in season-1 (Figure 1). However, this did not appear to cause any negative effects on soil moisture content during the following soybean season as the soil moisture contents in the cover cropped plots and fallow control treatments were similar (Figure 1). This does not support the perceptions that cover crops may deplete soil moisture which will cause water stress for the following cash crop.
Mixture of 5a, rye, and the mixture of rye and crimson clover produced the highest amounts of biomass, whereas mixture of 5b and the mixture of oat and radish produced intermediate and crimson clover and the mixture of crimson clover and turnip produced the least amounts of biomass in both seasons (Figure 3).
Mixture of 5a, mixture of rye and crimson clover, and rye had the highest water use efficiency values in both seasons (Figures 4&5). Water use efficiency is the ratio between biomass and water use. Since these cover crops (mixture of 5a, mixture of rye and crimson clover, and rye) did not utilize more water than other crops (Figures 1&2), the higher water use efficiency values of these cover crops are a result of their higher biomass.
Educational & Outreach Activities
We demonstrated the study and presented the results in the Clemson University Piedmont Research and Education Center field day. We also presented the results in professional meetings (ASA meetings). A manuscript is under preparation to submit to a peer-reviewed journal. These efforts 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.
The conventional grain crop producers rely primarily on herbicides for weed control. On the other hand, organic grain crop producers rely primarily on cultural and mechanical practices to manage weeds and consider weed control among their greatest production costs. Growing numbers of grain crop producers are adopting sustainable and organic 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 U.S. (it has reached a record of 4.1 million acres in 2016, which is 11% increase compared to 2014). Thus, development of more effective non-chemical weed management strategies can have substantial positive economic and environmental impacts, as far as conventional and organic grain crop production are considered. The use of cover crops offers a more sustainable, systems-based approach to weed management than herbicides and tillage.
Cover crops reduce weed pressure and improve soil health and cropping system diversity, but they also use soil water, thus affecting soil water relations of the following cash crop. Therefore, if the cover crops are not water-use-efficient, it will cause additional irrigation cost for the producers, leading to poor economic viability of cover cropping practices. This project aimed at identifying the ‘water-saver’ or water-use-efficient cover crops and thus, improving the efficiency of utilization of an important on-farm resource, water. The project addresses some roadblocks to producer adoption of cover cropping by (1) identifying single species or mixtures of cover crops that produce large amount of biomass without increasing water use, (2) generating data on water use by cover crops compared with conventional fallow practices, and (3) disseminating research results to producers, extension agents and other researchers through presentations and publications. These efforts may result in greater adoption of cover cropping by grain crop producers, reduced use of herbicides, and development of soil organic matter leading to healthier soils. In addition, the use of water-use-efficient cover crops will improve the availability of soil water, which could reduce irrigation cost and thus improve the economic feasibility and sustainability of cover cropping practices.
While sustainability is a common topic in agriculture during recent decades, the practices to implement it was not clear to my understanding. At the beginning of my graduate journey, I imagined brilliant and grandiose actions to reduce atmospheric CO2 as ‘’sustainability’’ actions, but this project taught me that planting cover crop in the off- growing season to bring diversity and cover the soil is also valuable as long as the farmer can grasp the principle behind it. The collaboration with the farmers in their context has been very instructive to me at distinct levels. This project has allowed me to bridge my rigorous academic formation to the very needs of the collaborative farmer who is the decision-maker at the end of the day. It sparked my curiosity about the indicators to look up for soil improvement while working. This project was also a means to improve how I communicate science to the public. This project helps our lab acquire different equipment that I have been able to learn how to use to conduct our research. This project channeled my passion but also fueled it to bring my contribution to a better world.