Measuring the Effects of Manure Applications on Sheet and Rill Erosion During the Critical Period on Cropland Utilizing a Portable Rainfall Simulator

Soil erosion models are becoming increasingly accurate and now can simulate a variety of surface covers. Surface covers can lessen erosion by reducing detachment and movement of soil particles; thereby, reducing sheet and rill erosion. Different kinds of animal manure applications are credited in these models by increasing the surface cover percentage and reducing the runoff curve numbers. The accreditation of these manure applications to surface cover and to changes in runoff curve numbers were determined through bench test studies under laboratory conditions. Several studies using rainfall simulators have also been conducted to measure the effects of manure application on runoff and erosion. These rainfall simulation studies have been conducted in laboratories and at field sites. Nutrient management policies and strategies encourage manure application to occur as close as possible to when crops are in the most need of nutrients, such as nitrogen and phosphorus. Our study focused on corn crops during the vegetative growth stage when the canopy cover is not fully established. Manure applications during this time could provide significant benefits by increasing soil surface cover to protect the soil from rainfall impact/erosion during this critical period. On-field rainfall simulation studies were conducted in North Carolina in order to provide state specific information based on local soils using local representative rainfall rates. Soil for this study was collected in lysimeters from fields managed under long-term no-till and conventional till for over 15 years. Undisturbed soil monoliths were collected from fields located in North Carolina. The no-till soil was a Enon fine sandy loam and the conventional till soil was a Nathalie sandy loam. The soil monoliths were placed in perforated metal trays which had a depth of 6.4 cm. These soil trays were designed to simultaneous measure runoff and percolation during rainfall simulation. The surface area of each experimental unit was 0.3 m by 6 m. Sediment yields and runoff amounts from the experimental samples were compared to a control (no manure applied) to determine potential reductions in soil loss that can be attributed to different rates and types of manure applications. Dissolved phosphorus levels were also examined in the runoff effluent and compared to each manure application rate samples. Table 1 reports the total sediment losses from three types of manure applications at five different rates from the rainfall simulations applied. The manure greatly reduced soil loss, especially from the conventionally-tilled treatment.