A five-year study by a New Mexico State University researcher found that integrating cover crops, such as legumes and grasses, into existing cropping systems can increase the biological health of soils on hot and dry semiarid lands.
Led by NMSU cropping systems agronomist Rajan Ghimire, the study is part of efforts by the NMSU College of Agricultural, Consumer and Environmental Sciences to improve soil health in New Mexico.
Ghimire, an assistant professor with research interests in soil health, soil fertility and conservation systems, began the project in 2015 shortly after joining the NMSU Agricultural Science Center at Clovis, part of the college’s statewide system of research centers known as the Agricultural Experiment Station.
The study – a collaboration between weed scientists, agronomists, agri-economists and soil scientists from the NMSU Agricultural Experiment Station centers in Las Cruces, the United States Department of Agriculture’s Agricultural Research Service and Colorado State University – is the result of Ghimire’s desire to understand soil-plant-environment interactions through a systems-based research approach.
“We need a systems approach in research to understand complex systems such as agricultural fields,” he said.
Ghimire started the study, he said, as a cropping systems project with eight different cover crop treatments in three-year crop rotation, using start-up funding. He later received funding from the NMSU Agricultural Experiment Station, the USDA-National Institute of Food and Agriculture, and the Natural Resources Conservation Service to continue the study through 2021.
“The purpose of this study is to integrate diverse cover crops and mixtures in existing cropping systems of semiarid regions and improve soil health and environmental quality while sustaining crop production in dryland and limited-irrigation cropping systems in New Mexico,” he said.
Today, Ghimire’s study covers a four-acre area at the NMSU Agricultural Science Center at Clovis. He has evaluated cover crop treatments that include different combinations of grasses, legumes and brassica, or cabbage plants.
In third and fourth years of the study, he said, results showed cover crops increased the biological health of soils.
“We evaluated soil health, carbon sequestration, greenhouse gas emissions, soil water dynamics, weed suppression, and yield of subsequent wheat and sorghum crops – with and without cover crops,” he said. “We also analyzed the economic feasibility of various cover cropping practices.”
The response of soil organic matter pools and biological component varied with cover crops, Ghimire said. Legumes and their mixture with other cover crops were the most effective in improving soil biology, he added, but oats and their mixtures were most effective in increasing organic matter. Other benefits included better weed suppression and greater ground cover.
“There is some skepticism on the effectiveness of cover cropping in the hot, dry, semiarid environments, such as New Mexico,” he said. “However, more farmers are becoming interested in recent years, and acreage is increasing every year.”
But cover crop treatments require careful planning, Ghimire said.
“Cover crops need moisture,” he said, “and careful selection of species, planting and termination timing, and residue management after cover crop termination determines the yield of the subsequent crop, specifically, in drylands. If cover crops are integrated with irrigated cropping systems, the benefits could outweigh any risk.”
Good soil structure and high organic matter are two major indicators of soil health, Ghimire said. In hot, dry environments, such as the Southern High Plains region that spans New Mexico, Texas, and Oklahoma, crop production and organic matter storage face limitations caused by low precipitation, he said. Eastern New Mexico, in particular, averages about 18 inches of precipitation annually.
“Cover crops can increase biomass input and support soil organic matter accumulation,” he said. “At the same time, they improve soil structure and conserve soil from both wind and water erosion.”
Cover crops also increase carbon input to soils through their root and aboveground biomass and root exudates, which provide food for microbes, such as bacteria and fungi, and support their activities in the soil, he said.
Ghimire will continue his cover-crop study through next year, but is seeking additional funding to keep the research going as a long-term study.