Yuma Ag & You: Turn under, don’t burn your stubble
Come on, folks! Are you still burning your wheat stubble? Really? It is hard to believe that some growers find it better for their soil to burn the stubble, sterilizing the top few inches and adding salty ash to the soil surface.
Soil health is a growing problem in our intensely farmed Yuma County. The desert soils we farm naturally have less than one-half percent organic matter, compared to Midwestern soils with up to 5% organic matter. Making it harder for the soils to retain organic matter is our tillage, irrigation and hot temperatures.
What is organic matter? It is that part of the soil composed of anything that once lived. It includes plant and animal remains in various stages of decomposition, cells and tissues of soil organisms and substances from plant roots and soil microbes.
Growers in Yuma commonly add composted manures as organic matter to improve the soil structure; open the soil so air, water and roots can easily penetrate; and aids the growth of crops by improving the soil’s ability to store and transmit air and water.
These manures also contain some nitrogen which the soil microorganisms use to help break down plant materials that have been returned to the soil.
It is becoming more common after wheat harvest that the stalks are baled and the stubble has compost applied to it before being disced into the soil. The field is then irrigated to provide the necessary moisture for the organisms to break down the stubble.
When soils are tilled, organic matter is decomposed faster because of changes in water, aeration
and temperature conditions. The amount of soil organic matter is controlled by a balance between additions of plant and animal materials and losses by decomposition. Both additions and losses are very strongly controlled by management activities.
Yuma County growers are continually working to reduce the number of times that the soil is disturbed in the fields. Multiple tillage operations during field preparation are done at the same time, rather than singly.
This not only saves labor
and reduces machinery costs, it reduces the compaction of the soil. Compaction reduces the size of the holes between soil particles (pores) which are essential for air and water to move through the soil as well as providing pathways for plant roots.
The roots left after crop harvest also are organic matter, and as they decay, they leave open channels, again important for air and water movement. Planting crops with a fibrous root system like Sudan grass, corn, sorghum and wheat leave roots 3 to 4 feet deep. Since most produce crops have 18 inch roots or less, the soil below the root zone stays wet and contains nutrients that moved below the vegetable roots.
A discing to knock down rows followed by one of the fibrous rooted crops that utilize both water and nutrients in the deeper soil layers is ideal. When that crop is harvested, the soil is extremely dry to a 3-foot depth and chiseling will shatter any compacted layers. Tillage should never be done on wet soils.
Healthy soils produce great crops. Turn under, don’t burn your stubble!