Residue in a growing crop Kay Ledbetter, Texas A&M AgriLife
Early cover crop termination can result in residue that rapidly degrades or blows away.

Don't rush your cover crops

Like a good wine, cover crops get better at their job as they age.

Often producers with cover crops worry about moisture use, but more important is the maturity of the crop residue and its beneficial results, says a Texas A&M AgriLife research scientist.

Paul DeLaune, an environmental soil scientist at Vernon, Texas, says when he talks about the residue management of cover crops, one question he always gets concerns termination timing and the use of soil moisture by the cover crop.

Cover crops are designed to keep soil from moving and from overheating, and to improve soil life and soil quality. DeLaune has included Austrian winter field pea, hairy vetch, crimson clover, wheat, rye, turnips and radishes as cover crops in his various studies.

“We use neutron probes here to monitor soil moisture year-round, and yes, the cover crop does use soil moisture,” DeLaune says. “But one thing we’ve found is that soil moisture is quickly recharged and your crop is back to status quo if you get a rain between termination and the planting of your cotton.”

DeLaune is referencing eight different cover crop studies by AgriLife Research in the Texas Rolling Plains where soil moisture is monitored throughout the year, some continuously since 2012. Because he is in the southern High Plains, he talks about cotton as the next crop. The principles, however, are very similar for grazed crops and resultant residue.

Allowing the plants to mature develops more carbon, which takes soil bacteria and other life longer to break down and consume.

To prove his point, DeLaune compares two different termination timings with a wheat cover crop.

“I like to let it go ahead and mature out to about 50% heading or so, and then plant cotton four to six weeks after termination,” DeLaune says. “This year, we had to terminate a little earlier due to a drift issue – mid-March versus toward the end of April.

“What we determined is if you terminate too early, you’re not going to have lasting residue. The residue in a vegetative stage degrades very rapidly. If you can allow wheat to reach heading, you can see lasting residue for about 18 months.”

Even though you may be in a low-rainfall area, it will pay off in the long term to build up the soil organic matter in your system, DeLaune says.

“Although soil organic matter is slow to build up in our environments, we have seen more immediate impacts off cover crops on soil physical properties such as soil strength and infiltration,” he says. “Within the Rolling Plains, we have not observed depleted soil moisture behind cover crops during wheat and cotton growing seasons in dryland cropping systems.”

DeLaune says he understands there is greater risk in dryland systems and drier environments moving further west. However, Katie Lewis, AgriLife research soil scientist at Lubbock, has noted the same trends in irrigated cotton systems at Lamesa.

Source: Texas A&M University

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