R.E. Sojka

Removal of Vegetative Clippings Reduces Dissolved Phosphorus Loss in Runoff

Rainfall simulation was used to study the vegetative filter strip (VFS) conditions under which losses of total dissolved phosphorus (TDP) and dissolved reactive phosphorus (DRP) leaching occur. Boxes containing silt loam soil were planted with ryegrass and cut at two different intervals prior to simulated rainfall 14 days apart. Grass clippings were either removed or retained. During the second simulated rainfall, runoff TDP and DRP were greater for treatments cut the day before irrigation with clippings retained as compared to treatments cut the same day as irrigation with clippings retained. Removing clippings yielded the lowest mean TDP and DRP concentrations. Increasing the senesced vegetative surface area for contact with water, and the amount of time for leaching to occur, resulted in the greatest DRP loss. The VFS management implications should consider clipping removal or no or reduced mowing during the growing season followed by end-of-season removal to reduce DRP leaching losses.

Technologies to Minimize Water Quality Impacts of Irrigated Agriculture.

Irrigation transformed arid land in the Pacific Northwest into productive agricultural land. However, much of this land is prone to erosion during irrigation, which can cause problems on and off of the field. Management practices have been developed to control soil erosion on irrigated land and improve the quality of water returning to streams and rivers. Applying polyacrylamide (PAM) with irrigation water can reduce erosion from furrow irrigated fields more than 90%. Using PAM in combination with other practices, such as applying straw mulch in furrows and installing small sediment ponds on fields, can virtually eliminate sediment loss fromfields. Once soil runs off a field, it can be removed by settling in sediment ponds, although soluble nutrients remain in the water. Applying 20 mg/L alum to irrigation return flow water can remove about 50% of the soluble phosphorus that will not be removed as suspended sediment settlesin ponds. Using these management practices allows irrigation to continue with minimal impact on water quality.

Aggregate Tensile Strength and Friability Characteristics of Furrow and Sprinkler Irrigated Fields in Southern Idaho

Agricultural crops grown in southern Idaho are furrow or sprinkler irrigated. Therefore, the soil experiences several wetting and drying cycles each growing season that can contribute to changes in aggregate tensile strength and friability. The objective of the research was to evaluate the influence of irrigation on soil structural properties. Four furrow-irrigated fields were sampled at the top and bottom of the field, in the furrow and on the bed location of the furrow. Five sprinkler-irrigated fields were sampled at depths of 0–5 and 5–15 cm and at the top and bottom of the field. Results from this study indicate that differences in tensile strength in furrow-irrigated fields were only evident soon after irrigation; otherwise, there were few differences in tensile strength and friability. In sprinkler-irrigated fields tensile strength increased with depth in three of the five fields measured. Friability was less affected by depth.