Date of this Version
FIELD CROPS, G-8, Cropping Practices Issued April 1981, 15,000.
Crop residues are playing an increasingly important role in today's agricultural management systems. In the past, residues were normally chopped or disked and plowed under in the process of seedbed preparation. Distributed throughout the deep-tillage layer, the residues decomposed rapidly and recycled organic matter back into the soil. Use of the traditional moldboard plow tillage system also provided a loose, residue-free seed bed. Unfortunately, moldboard plow tillage systems have high soil moisture losses which can reduce yields in low rainfall areas or during dry years.
Incorporating previous crop residues also leaves the soil surface exposed to agricultural runoff which causes soil erosion. Erosion and subsequent sedimentation have been identified as Nebraska's major water quality problem. Approximately 75 percent of the erosion from agricultural land is from row crop areas. In addition to removing valuable top soil , soil erosion removes crop nutrients, pesticides and other materials which may cause water quality degradation.
Residue management through the use of conservation tillage systems is the most cost-effective method for controlling wind and water erosion. Using crop residues to protect the soil surface from rainfall can reduce water erosion by 90 percent. Adopting these tillage systems also reduces fuel, labor and time requirements and conserves soil moisture. See NebGuide 080-535, "Tillage Systems for Row Crop Production," for more information on conservation tillage systems.
Erosion is initiated by the detachment of soil particles from clods and other soil aggregates. A large portion of soil detachment occurs upon raindrop impact which, during an intense thunderstorm, can loosen and detach up to 100 tons of soil per acre (224 mt/ ha). Depending on slope and soil characteristics, this loosened soil is transported and removed by agricultural runoff, which dislodges additional soil particles while flowing across unprotected soil surfaces.
Residue management provides a means for limiting both soil particle detachment and removal from the field. Vegetative residues protect the soil from impact by dissipating the energy of the raindrops. Residues also create an intricate and complex series of diversion dams that slow the runoff water rate and reduce the amount of soil particle detachment. In addition, slowing the runoff rate reduces its capacity to transport dislodged soil particles from the field, thus reducing the erosion rate even more. Moisture conservation also occurs because more time is available for water to infiltrate the soil.
The amount of crop residue produced and subsequently available for erosion control depends mainly on the type and yield of the crop grown and the tillage system used. Generally, higher yields mean more residues. Although corn will produce more residue than soybeans (Figure 1), soybeans and small grain residues contain a large amount of stem material. On an equal weight basis, this stem material can be more effective in controlling erosion than corn residue. Although the amount of residue grown is important, the amount present from seedbed preparation through crop establishment is critical because the greatest potential for erosion in row crop production areas occurs from late April to mid-June. The selection and use of a tillage system largely determines the amount of residue cover during this critical period.