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New Mexico State University

New Mexico State University

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Tall standing crop stubble in fields helps conserve natural resources

CLOVIS, N.M. - Tall standing crop stubble left in a field after its harvest benefits next year's crop by protecting the soil and increasing water efficiency, as well as other advantages.

From left: New Mexico State University crop physiologist Sangu Angadi, Sultan Begna, a research specialist, and Wahby Ahmed, a visiting scientist, look over a field of tall standing crop stubble at the Agricultural Science Center at Clovis. Research has shown that leaving tall standing crop stubble after harvest helps conserve natural resources.(NMSU photo by Darrell Pehr)

New Mexico State University's Agricultural Science Center at Clovis has received a $75,000 grant from the USDA to allow Sangu Angadi, a crop physiologist, to continue his research into the benefits from the proper management of crop stubble.

In the Southern Great Plains, of which the eastern part of New Mexico is a part, crops are exposed to severe environmental stresses including high winds and high intensity rainfall that can lead to erosion.

"Strong winds in the region frequently cause wind-blown soil abrasion injury ... of delicate seedlings of crops over a large area, often severe enough to need replanting. Therefore, agriculture in the region can benefit both directly and indirectly from proper stubble management," Angadi said.

Technologies are available to leave tall standing stubble and later plant in that standing stubble, Angadi said. Proper management can help conserve the moisture, especially during the off-season, and increase the fraction of that used in transpiration, the process where moisture is given off through the surface of leaves and other parts of the plant.

Traditional no-till practices focus more on reducing soil disturbance than on stubble management.

"Tall standing stubble alters the energy balance and creates a favorable microclimate for crops," Angadi said. "Since less crop residue passes through the combine, energy efficiency of harvesting also can improve by leaving taller standing stubble in the field."

Angadi advises leaving 15 inches of a crop to reap the greatest benefits.

Visual observations at the Clovis science center showed better infiltration of rainwater with standing wheat stubble compared to cultivated field. Snow trapping also seems to improve with tall standing stubble.

Recent studies, Angadi said, have shown that tall standing stubble reduces wind speed and solar radiation reaching the soil surface. There are indications that reduced turbulent air mixing, due to reduced wind velocity and reduced solar radiation by tall standing stubble, are enough to reduce evaporation, but not enough to reduce plant photosynthesis.

"An estimation using the Bowen ratio approach in the Southern Great Plains by other researchers indicates a 26 percent reduction in evaporation," Angadi said.

The height and number of stems per unit area seems to influence the effectiveness of tall standing stubble management, Angadi said. Frequent surface wetting by center pivot irrigation, in which evaporation loss is often energy limited, can benefit more from the reduced evaporation losses. The major changes in the microclimate are noticed early in the growing season, when the crop canopies are small and cannot regulate evaporation loss on their own. This also will help in reducing the direct wind damage to seedlings.

Angadi said most studies that look at the benefits of tall standing stubble ignore the effect of the microclimate on crop seedling growth.

"In a typical no-till system, solar radiation is reflected back by the flat stubble and that results in cooler soil temperatures and slower seedling growth. However, in tall standing stubble, the solar radiation is trapped within the standing stubble," he said.

As a result, he added, although the soil temperature is lower than in cultivated fields, the temperatures of seedlings are often higher. Unless clouds blocked the sun, the plant temperatures were warmer in a three-year observation. On a bright and sunny day, a seedling growth in standing stubble was warmer by up to 9 degrees Fahrenheit, which is a useful heat in the cool early spring.

In addition, wind moderation by tall stubble seems to protect seedlings from convective frost. Increased efficiency of using water in transpiration by the tall standing stubble is beneficial. Faster growth of seedlings early in the season is seen as a cumulative effect of all of these benefits.

There are some limitations to leaving crop stubble in a field after the harvest. Farming mentality, Angadi said, is to keep the field clean and the soil in good health, giving the impression that the field is "ugly" if it is not tilled.

A no-till drill is required for planting in the residue.

If too much stubble is on the ground, soils can be cooler. Tall standing stubble should not have this problem, but more data is needed to prove it, Angadi said.

Having crop stubble also requires different weed and fertility management strategies.

There is an impression, Angadi said, that if soil is smooth and not tilled to create a cloddy surface, intense rainfall water may not infiltrate and the rainfall would be lost. In reality, Angadi said, stubble may slow down water runoff and provide channels for infiltration.

Despite the limitations, the benefits to using tall standing stubble are great. Angadi said the process helps farmers be more aware of the natural resources they have available to them and helps them to be more efficient and conservative of those natural resources, while maintaining productivity.