By Ruth Beck, Extension Agronomy Field Specialist; Anthony Bly, Extension Soils Field Specialist
This year’s wheat crop produced a good amount of straw and many growers have chosen to cut and bale the straw to gain some extra income. It is tough to put a dollar value on crop residue and its contribution to land productivity. However, there are some important considerations that growers may want to examine before baling small grain residue.
Crop Residue Nutrients
There are nutrients in crop residue. South Dakota State University (SDSU) data shows that wheat stover contains approximately 10 pounds nitrogen (N), 3 pounds phosphorus (P2O5), 31 pounds potassium (K2O), and 2 pounds sulfur per ton. The value of these nutrients combined is about $26.00 per ton wheat stover.
According to research from South Dakota, the weight of stover is approximately equal to just less than the weight of the harvested wheat. A 20-bushel wheat crop can produce approximately 1,200 pounds of stover (60 pounds x 20 bushels). A 60 bushel-per-acre wheat crop (3,600 pounds stover) can hold approximately $46.00 worth of nutrients per acre. Knowing this value and adding it to the cost of labor, machinery and supplies needed to bale the straw may make producers think a little longer before baling crop residues.
The direct financial costs of baling crop stover may be the most easily estimated cost associated with crop residue harvest, but other effects of residue harvest on the soil are even more important.
Defense Against Soil Erosion
Crop residues play an important role in reducing soil erosion from wind and rain. Wind erosion can be especially damaging during long periods of drought and open winters in South Dakota. Blowing soil can reduce air quality, affect human and livestock health and cause traffic accidents. Residue on the soil surface reduces the wind velocity at the soil surface, keeping soil in place and protecting seedlings, which can be damaged by windblown soil particles. Taking part of the residue may seem harmless, but it decreases soil organic matter levels as compared to leaving it in the field. Grazing the residue using proper techniques leaves most of the value behind.
Old crop residues also prevent water erosion from storm events that include heavy rains. These precipitation events can cause sheet, rill and gully erosion. Soil loss also results in the movement of nutrients and pesticides into the water system. The rain drop impact on an unprotected soil surface will result in reduced aggregate stability and size, making soil more prone to erosion. Topsoil is a valuable resource to South Dakota’s growers, and losses from erosion are difficult to overcome and replace.
Preventing Water Loss & Temperature Fluctuations
Crop residue acts as a mulch on the soil surface, reducing soil water loss through evaporation and catching snow during the winter. In the spring of 2013, soil moisture was measured in side by side fields, both with residue from 2012’s wheat crop. One field had residue that measured 32 inches tall and the other had residue that was 8 inches tall. There was 1.2 inches more plant-available moisture in the field with the taller residue. In addition to the 7-10 inches needed to grow a healthy corn plant under water-limiting conditions, a corn crop is expected to produce 12 bushels of corn per inch of available water.
Crop residue can also protect the soil from temperature fluctuations. High soil temperatures resulting from high air temperatures could impact crop root growth and negatively affect soil microorganism activity. Soil microorganisms play an important role in plant and soil health.
Sustaining Organic Matter
Possibly the most important role that crop residue provides is sustaining and building soil organic matter. Soil organic matter contributes directly to the nutrient availability, nutrient retention capacity, and water-holding capacity of a soil. Soils with higher organic matter naturally resist erosion because they have better aggregate stability. This allows for increased aeration, water infiltration and drainage. Soil organic matter is maintained through decomposition of plant biomass returned to the soil. Soil organic matter levels in cultivated fields have been greatly reduced from native levels. Removing residue will reduce them even more. It is difficult to estimate the value of maintaining and building soil organic matter levels in South Dakota’s soils, however it is often observed that soils with higher levels produce better yields.