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Crop residue decisions affect soil life

In some ways, farming is like cooking. Cooking would be much easier if we could leave the kitchen after eating and not come back until we make the next meal. But someone needs to put away the leftovers, do the dishes and clean up the table.

Similarly, there’s work to do in farm fields after harvest and before planting the next spring, especially when it comes to the crop residue left behind.

No-till and prescribed fire are two potential ways to manage crop residue. Both practices help keep organic matter and nitrogen in the soil. However, research was needed to understand how these two practices can affect long-term soil health.

Lisa Fultz, researcher at Louisiana State University’s AgCenter, and her team want to help farmers deter­mine the best way to manage their residue between growing seasons. To do this, they decided to learn more about how no-till and prescribed fire manage­ment affect nutrients and microbes in the soil. The AgCenter team focused their research on wheat and soybean rotations and continuous corn production systems.

“Common practices, like conventional tillage, are highly disruptive to the soil,” Fultz said. “The need to identify viable conservation practices is growing in importance.”

Both no-till and prescribed fire cause minimal phys­ical disturbance to the soil, but they also come with drawbacks. No-till can create poor conditions for crop growth, such as cooler soil temperatures and increased moisture, which promote disease. Burning off the previous crop debris with controlled fire can leave bare soil vulnerable to erosion.

Crop residue and its degradation by soil microbes is an important part of the carbon cycle. Plants store carbon during the growing season, then microbes use the plant residue for food. The carbon then gets stored in the soil in a chemically stable form.

“Fresh, green material in no-till fields is easy to break down and provides rich nutrients for soil microbes,” Fultz said. “Ash from burned residue is more chemically stable, but it doesn’t provide a nutrient source for microbes.”

The team found that impacts from crop management practices, such as crop rotation or fertil­ization, outweighed the influence of prescribed fire for residue management. Researchers found some decreases in microbial activity after yearly prescribed burns.

Findings show prescribed fire had some possible short-term benefits for soil nutrient availabil­ity, but timing is crucial. Prescribed burning of wheat residue provided an increase of nitrogen for about seven days. These benefits should be weighed against other possible impacts, such as carbon dioxide production and crop yield.

“We still need to learn the long-term influence of prescribed fire on the soil biological com­munity,” Fultz said. “While short-term impacts were measured, the long-term influence on soil nutrients, biological cycles and soil health are not known.”

No two farm management systems are the same, and their success is defined by the user. Scien­tists continue to examine possible scenarios to provide accurate and sustainable recommendations to farmers.

“I have always been interested in soil conservation and its potential to impact many facets of life,” Fultz said. “By improving soil health, we can improve air and water quality, store carbon, and provide stable resources for food production.”

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