Submitted to: Fluid Journal
Publication Type: Trade journal
Publication Acceptance Date: 9/5/2006
Publication Date: 10/1/2006
Citation: Kovar, J.L. 2006. Fall Surface-Applied Fluid P Movement Into Soil Limits Potential Loss to Erosion. Fluid Journal. 14:14-16. Interpretive Summary: Phosphorus (P) is an essential nutrient for growth of crops and often needs to be applied to the land for optimal crop growth. To be effective, however, the fertilizer must increase the amount of plant-available P in the soil, and the plant root system must be able to take advantage of this increase. With a field experiment, we found that the P in liquid fertilizer dribbled on the soil surface after soybean harvest had moved into the soil. The highest concentrations were found three weeks after application, but at least some of the applied P could still be detected the following spring. The results of two years of measurements suggest that P applied to the soil surface after crop harvest will move into the profile, where it will be less subject to loss in runoff or by erosion during the winter months. The results of this research will benefit both commercial growers and the fertilizer industry by providing nutrient management alternatives that maximize crop utilization and minimize potential nutrient losses.
Technical Abstract: Recent research has shown that surface dribble applications of P fertilizer increase P bioavailability within several weeks of application. We hypothesized that increased levels of bioavailable P in the root zone also would be measurable in the spring, following a surface band application of liquid fertilizer in the fall of the previous year. Our objective for this study was to evaluate the positional and temporal availability of P from surface bands of fluid fertilizer following fall application. Differences between two P sources also were investigated. Field plots were established on a Canisteo silty clay loam in central Iowa. The study was initiated in the fall of 2003, and repeated in 2004. Exchange-resin membranes were used to characterize P movement. Treatments consisted of a control, 0+50+0, and 17+50+17 liquid fertilizer dribbled (35 gal./A) on the soil surface two inches to the side of the previous soybean row, following crop harvest. Higher concentrations of bioavailable P were measured greater than one inch below the soil surface for both of the P sources three weeks after application in both years. Measurements made in the spring of 2004 at 20 and 23 weeks after application showed that relatively higher levels of bioavailable P were still present in the top six inches of the profile. In the spring of 2005, however, we could detect fewer differences in relative amounts of bioavailable P from measurements made 15 and 19 weeks after application. Low levels of soil water at the time of the measurements probably limited P diffusion. Nevertheless, the results of these two years of measurements suggest that P applied to the soil surface after crop harvest will move into the profile, where it will be less subject to loss by erosion during the winter months. These studies are being repeated in 2006.