Soil erosion is sometimes excessive during furrow irrigation and under center pivot sprinkler systems. An understanding of erosion processes is required to predict and develop management practices to reduce irrigation induced erosion. Little erosion process research has been carried out under irrigation, but much of the extensive channel sediment transport and rainfall-induced erosion process research can be adapted to irrigated conditions. Soil erosion occurs when fluid in motion detaches and transports soil particles. Sedimentation occurs when the fluid transport capacity decreases to less than the sediment load. Hydraulic forces of moving water and soil factors such as aggregate stability and particle size determine erosion and sedimentation. Under furrow irrigation, the shear of the overland flow against the soil provides the detachment force and is a primary factor determining channel transport capacity. With sprinkler irrigation, water drop energy detaches particles, some of which may be transported downslope by shallow interrill flow if the water application rate exceeds the soil infiltration rate.
No abstract
A rainfall simulator study was conducted on a Sidell silt loam (Typic Arguidolls, fine‐silty, mixed, mesic) in northwest‐central Indiana to evaluate the effectiveness of different lengths and percentage covers of cornstalk residue strips in reducing total nitrogen and available phosphorus discharges associated with the sediment. A 2.7‐m long residue strip with 50% surface cover reduced nutrient discharges by about 70% when the nutrient loads entering and leaving the residue strip were compared. Reductions in sediment and nutrient discharges with increasing length and percentage cover of the residue strips were almost proportional.The sediment was separated by sieving and gravity sedimentation into 10 size fractions ranging from > 2 to <0.002 mm in diam. About 50% of the sediment entering the residue strips was composed of particles >0.05 mm. The 2.7‐m long residue strip with 50% surface cover filtered out most of the particles >0.05 mm. As a result, 85% of the sediment leaving this residue strip was in the <0.035‐mm size fractions.Nutrient concentrations of the fractions >0.21 mm entering the residue strips were higher than those concentrations of the 0.05‐ to 0.01‐mm fractions entering the strips. Nutrient concentrations of the fractions <0.21 mm and >0.01 mm increased as the sediment moved through the residue strips, with the effect being related to residue length and percentage cover. Residue reduced the transport capacity of runoff below its sediment load, which caused the denser particies within these size fractions to be deposited. The less dense particles that were not deposited were composed of a greater proportion of small silt and clay primary particles, which increased the nutrient concentrations.
To gain a better understanding of the interactions between soil detachment, transport capacity, and residue cover, the USDA programmable rainfall simulator was used to erode plots created on established and newly created ridge‐till areas of <1% slope with and without residue cover. A control of conventional moldboard plow‐spring disk was also included. Results showed that for all treatments, ridge sideslope erosion was three to four times greater than total soil loss, suggesting that transport capacity was the limiting factor. For most runs no significant difference in soil loss was measured between ridges of different ages. The presence of residue decreased soil loss to one‐sixth or one‐seventh on older ridges and to one‐half on new ridges. Location of residue was more important than the total amount of residue. Residue placed only on the furrow bottom was as effective in reducing soil loss as residue placed over the entire ridge and furrow, while residue placed only on the ridge side‐slope did not reduce soil loss significantly from treatments without residue.
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