By Sangu Angadi
In the semiarid climate of the southern Great Plains, strong winds promote evaporation and wind erosion, while unpredictable precipitation patterns expose crops to severe environmental stresses and the high intensity of rains often leads to water erosion.
Strong winds in the region frequently cause wind-blown soil abrasion injury (sand blasting) of delicate seedlings of crops over a large area, often severe enough to need replanting. Therefore, agriculture in the region can benefit directly and indirectly from proper stubble management.
Technologies are available to leave tall standing stubble and later plant in that standing stubble. Stubble management practices can help in conserving the moisture, especially during the off-season, and in increasing the fraction of that used for transpiration.
Traditional no-till practices focus more on reducing soil disturbance than on stubble management. In that system short stubble is standing and the rest of the crop residue is lying flat on the surface. Tall standing stubble alters the energy balance and creates a favorable microclimate for crops. Since less crop residue passes through the combine, energy efficiency of harvesting can also improve by leaving taller standing stubble in the field.
Better infiltration of rain water with standing stubble was evident in a field observation at Clovis. Snow-trapping improves substantially with tall standing stubble. Recent studies 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 indicates a 26-percent reduction in evaporation.
The height and number of stems per unit area seems to influence the effectiveness of tall standing stubble management. 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 will also help in reducing the direct wind damage to seedlings.
Most of the studies looking 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.
As a result, although the soil temperature is lower than in cultivated fields, the temperatures of seedlings are often higher. Unless the sun was blocked by clouds, the plant temperatures were warmer in a three-year observation. On a bright and sunny day a seedling growing in standing stubble was warmer by up to 9º F, which is a significant amount of 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 also beneficial. Faster growth of seedlings early in the season in tall stubble is seen as a cumulative effect of all of these beneficial effects.
Sangu Angadi is a crop physiologist at New Mexico State University’s Agricultural Science Center at Clovis. He can be reached at 985-2292, firstname.lastname@example.org