Scientists study long-term effects of conservation methods and soil variability

Soil conservation practices such as no-till systems, cover cropping and different rotations benefit producers, but LSU AgCenter researchers are working to determine the return producers can expect on this long-term investment.

Lisa Fultz, an AgCenter soil microbiologist, is examining soil conservation trials that have been conducted over the last eight to 10 years to determine how conservation practices improve soybean and grain production.

“When producers implement these conservation practices, regardless of what they are, many times they will see a yield decline immediately afterward,” Fultz said. “But we often expect to see a rebound after — usually around three to five years.”

One trial Fultz is studying has been in place for 10 years. After five years, the research showed a 25% to 30% increase in soil organic matter. Fultz is now studying whether there are further increases after five more years.

The initial yield decrease followed by yield increases occurs “because the biological system is resetting itself,” Fultz said.

As producers start introducing more biomass from cover crops, no-till residue or other organic matter, there is an influx of organic material, she said, and the microbes from that influx can outcompete cash crop plants for nutrients, especially nitrogen.

“Once they have established themselves in those communities, that excess nitrogen starts becoming available again,” Fultz said.

In research trials, soybeans do not show the same fluctuations (decreases and increases) in the first few years.

“Unfortunately, we don’t necessarily see yield benefit,” Fultz said. “From a yield perspective, it’s maybe not as beneficial. But it also means that they’re not having as much yield loss or really any yield loss so far.”

Trials have shown that corn can receive a “nitrogen credit” for the use of legume cover crops, Fultz said.

“We are seeing some benefit from them. We’re seeing increased organic matter,” she said. “The nutrient cycling enzymes that we measure, they are basically looking at the turnover of specific nutrients. We see them higher in areas where we have cover crops or no-till practices.”

Another trial that has been ongoing for eight years compares tillage versus no-till systems as well as multiple cover crop termination dates and different rotations. Fultz’s team is collecting soil samples and analyzing them.

Fultz is also examining data from two model farms included in an AgCenter program that institutes best management practices, a project made possible by grant funding from the Patrick F. Taylor Foundation. These analyses will help researchers make cover crop recommendations to soybean and grain producers.

“Can we make adjustments to seeding rate recommendations? Right now, for cereals, they’re kind of on the high side,” Fultz said. “When we compare data for the whole southern region, it is very likely that we can reduce those recommended seeding rates.”

Another AgCenter soil scientist, Xi Zhang, is in the middle of a three-year study on spatial variability of soil. His research asks how variations in soil affect soil water and nutrient management. 

“The reason I developed this project was to look at the spatial variability in agricultural fields and to look at how the changes in the soil texture or other soil properties are going to influence the water movement in the soil and how this can influence how the crop grows,” Zhang said.  

Zhang conducts research at a 4-acre field at the Red River Research Station that features fine-, medium- and coarsely-textured soils. His research team took soil samples with grid-based sampling method at 65-foot intervals, sampling three different depths up to 24 inches and measuring the soil texture. They used geostatistical analyses to create a map of the spatial variability of soil clay content. 

Based on the soil clay map, soil moisture sensors were installed in different zones at two depths — one zone zero to 8 inches deep and another between 8 and 24 inches. Compared with the high clay zone, the soil with a low clay content responded to water input more quickly, a result consistent with field observations. Water can easily permeate soils with a low clay content.

“Sometimes when we find an area of low yield, it is not caused by a nutrient deficiency,” Zhang said. “It is caused by water stress.” 

This year, the second year of a three-year study, Zhang is installing soil water samplers to measure how the change of the water dynamic in the soil can influence the transportation of nutrients. He also wants to simulate different rainfall intensities or irrigation practices to study soil water dynamics and nutrient transportation under diverse scenarios.  

In the third year of the study, Zhang wants to integrate soil and crop data to delineate management zones to convert research results directly into management decision support to help soybean and grain farmers to improve production.

“That is important, not just that the producer knows there is variability, but we want them to know how we are going to use that variability to improve management and yield,” Zhang said. Kyle Peveto

A soil moisture sensor is propped on a stand in the middle of a soybean field.

A soil moisture sensor installed in a field at the AgCenter Red River Research Station measures the status of fields used in Xi Zhang’s research. Photo by Xi Zhang

9/14/2023 3:12:25 PM
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