By DOUG SCHMITZ
AMES, Iowa – Excessively dry soil conditions this season make field preparation and tillage this fall challenging, even though a dry soil condition is preferred for conducting tillage operations, according to Mahdi Al-Kaisi, Iowa State University (ISU) professor of soil management.
“The dry, warmer-than-normal growing season this year presents significant challenges for managing soil and crop residue this fall,” he said. “The advantage of having low soil moisture for tillage is a reduced impact of equipment traffic in causing soil compaction and ruts in the field.
“However, soil disturbance under dry or any other conditions destroys soil structure and increases the potential for soil erosion after any rain events, and the loss of soil organic matter, topsoil and nutrients,” he added.
He said the lack of soil moisture – especially in the top 12 inches where most tillage occurs – can produce unfavorable conditions for soil fracturing.
“The excessive dry soil conditions can produce large soil clods that are not easy to break with secondary tillage in the spring,” he said. “Also, tilling excessively dry soils can be costly in terms of fuel and time use as compared to soils with normal field moisture at field capacity.
“The effectiveness of incorporating crop residue may be limited, and the lack of moisture will reduce the breakdown of crop residue,” he added.
Al-Kaisi said the best option for managing dry soils and crop residue under dry conditions is to limit soil disturbance, and keep residue on the soil surface.
“Crop residue can help mitigate drought conditions by trapping rain and snow moisture to recharge the soil profile for the following season,” he said. “It has been documented that keeping residue standing with no-till on the soil surface can trap 70 percent more of the water in rain or snow melt than conventional tillage.
“The water storage capacity of soil will be greater than that with conventional tillage, where soil structure is destroyed,” he said.
He said conservation practices play a major role in managing soil moisture.
“The absence or reduction of soil disturbance in no-till both minimizes soil moisture loss from the soil’s surface, and maximizes soil moisture storage,” he said. “They also enhance beneficial soil physical properties such as increased water infiltration, maintenance of soil macropores, and reduction of surface runoff during rain events, thus increasing soil moisture storage.”
Generally, he said, “Every tillage pass can cause the loss of one quarter inch of soil moisture; however, this number varies based on soil texture, soil organic matter content, and the amount of residue on the soil surface.
“Thus, with the unpredictability of weather and to ensure maximum soil moisture storage,” he added, “caution should be exercised in using tillage to manage dry soils this fall, and farmers should keep residue upright on the soil surface to increase the soil profile moisture recharge.”
Barbara Stewart, state agronomist with the USDA’s Natural Resources Conservation Service (NRCS) in Des Moines, said farmers should consider no-till farming as the most important tool to prevent loss of soil moisture – especially during the current drought conditions in Iowa.
“Drought management is a top concern right now,” she said. “With the drought conditions in Iowa – and across the Midwest – many producers are concerned about the next planting season.
“And with the extremely early harvest, many producers have more time on their hands for soil tillage operations,” she added. “The NRCS is recommending farmers use that time for something else more productive.”
She said soil tillage reduces soil moisture in several ways – the first being reduced water infiltration.
“Tillage reduces water infiltration by breaking up the large pores in the soil structure, which act as large diameter pipelines for water to soak into the soil profile,” she said. “Removing residue through tillage operations also leads to more soil erosion.
“The eroded particles of soil can then clog the smaller pores or pipes, further preventing infiltration and causing more soil runoff,” she added.
According to Iowa State University research, initial water infiltration rates are reduced from 5.67 inches/hour under no-till farming to 2.60 inches/hour under a soil tillage system.
She said other reasons to consider no-till farming as a soil moisture management tool include:
Every tillage pass can cause available plant moisture to drop .25 inch.
Crop residue moderates soil temperatures, reducing soil moisture evaporation, especially in the top two inches, and;
Corn stalks can help trap snow, which can add up to two inches of soil moisture after snow melt in the spring.
She said farmers concerned with soil moisture should visit their local NRCS office to discuss methods to help conserve, and enhance the water holding capacity of their soils.
She added some of these practices include no-till, strip-till, and cover crops.