Research HighlightsLong-Term Conservation Practices Improve Soil Chemistry
By Laura Temple
Introducing a change in agronomic practices can be compared to pressing the reset button on a computer or router. The practice change requires the soil system to restart before it establishes a new normal.
“We don’t know what that reset will look like, but with conservation practices, it often results in a crop yield hit as the soil microbes adjust,” explains Lisa Fultz, associate professor and soil microbiologist with Louisiana State University AgCenter. “But over time, those practices change soil characteristics, so the soil system can improve in quality — and crop yield.”
Thanks to years of research funded by the Louisiana Soybean and Grain Research and Promotion Board, Fultz and her team are analyzing those long-term changes in soil systems. This work will help farmers better understand the effects of conservation practices like incorporating cover crops and reducing tillage. Plus, she is leveraging that soy checkoff support into additional funding for her practical research.
“With 8 to 10 years of data, we can learn how soil health has evolved and changed the soil chemical characteristics,” she says. “Studying a variety of best management practices to determine the impacts they have will help create a toolbox so farmers can figure out what will work best on their farms.”
Based on a variety of past and current soil tests, Fultz is seeing patterns emerge as soils reset and respond to cover crops and no-till incorporated into typical crop rotations in Louisiana, including soybeans and rice, and soybeans, corn and cotton.
Fultz notes that crop yield recovery after incorporating cover crops or reducing tillage is location specific. In some areas, yield catches up to or exceeds previous averages in just a couple years, while in other fields, yields don’t rebound for 3 to 5 years.
“In general, soybean yields see less loss or gain after the introduction of a conservation practice,” she says. “On average, corn yields take a couple more years to recover, while we don’t have enough information yet to see yield recovery trends in cotton. The next question I hope to investigate is why this is. I anticipate those answers will build on what we have been learning.”
Her current research explores the long-term benefits that offset initial risks and the yield lag associated with the soil system reset.
Cover Crops Increase Microbial Activity
Fultz and her team have looked at single cover crop species and mixes, including grasses, legumes and some brassicas. In fields where farmers have used cover crops for several years, her team has measured both increased organic matter and enzyme activity.
“We did not see any direct changes in types of microbial communities in soils with cover crops, but we did see increases in the number of microbes,” she reports. “The increase in soil enzyme activity indicates that carbon and nitrogen are cycling. We see a greater turnover of nutrients thanks to cover crops.”
Cover crops scavenge nutrients, especially nitrogen. In Louisiana, those nutrients tend to be available in the spring, when cash crops need them. For example, some studies determined that legume cover crops can provide about 30 pounds of nitrogen per acre to the following crop, allowing reduced fertilizer rates, especially in corn.
“We thought we might see links between cover crop species and types of microbial communities,” she says. “However, we haven’t observed this beyond some weak trends.”
She also notes that grass cover crops can suppress weeds like Italian ryegrass and henbit well, while often requiring seeding rates 30 to 40 pounds per acre below common recommendations. However, she advises following recommended seeding rates for legumes and brassicas.
Reduced Tillage Stabilizes Structure
No-till or reduced till systems also increase soil organic matter content over time, according to the data Fultz and her team reviewed. Less tillage also correlates to improved aggregate stability, or how the soil holds together.
“Field rows maintain their integrity better in no-till systems,” she says. “That means farmers can reduce passes through the field and spend less time re-hipping rows over time.”
She adds that no-till systems have less runoff, especially under the high volume of rain often received in Louisiana. With more organic matter in the soil, all inputs are more likely to stay in place.
Fultz notes that cover crops and no-till systems do work together to influence soils. She recommends that farmers start small when introducing a new practice like cover crops. However, because soybean yield tends to be more stable, starting in soybean fields could help minimize the risks associated with changes.
Published: Sep 5, 2023
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.