Effects of Manure and Tillage on Edge-of-Field Phosphorus Loss in Seasonally Frozen Landscapes.

Environmental conditions and management practices affect nutrient losses in surface runoff, but their relative impacts on phosphorus (P) loss during frozen and nonfrozen ground periods have not been well quantified. More specifically, the relative importance of manure application, tillage, and soil-test P (STP) has not been assessed at the field scale. In this study, we compiled a dataset composed of 125 site-years of data from 26 fields that were continually monitored for edge-of-field P loss during snowmelt and storm events. Regression tree analyses were performed to rank the level of influence each environmental and management factor had on nutrient loads. Dissolved P (DP) was the majority of the total P (TP) during frozen conditions, but a small portion of TP during nonfrozen conditions. Manure application had a greater influence on the flow-weighted mean concentrations (FWMCs) of TP and DP during frozen conditions than during nonfrozen conditions. No-till resulted in greater TP and DP FWMCs during frozen conditions than conventional tillage, whereas the opposite effect for TP FWMC was seen during nonfrozen conditions. However, regression tree analysis revealed that STP (0- to 5-cm depth) was the most important factor in predicting DP and TP FWMCs during frozen conditions and DP FWMC during nonfrozen conditions. Extremely high STP values were associated with late-frozen manure applications and grazed pastures. Reducing surface P loss in seasonally frozen landscapes will require prioritizing management strategies that avoid manure application through early- and late-frozen conditions and lead to a drawdown of STP, particularly in the top 5 cm.

At-grade stabilization structure impact on surface water quality of an agricultural watershed.

Decades of farming and fertilization of farm land in the unglaciated/Driftless Area (DA) of southwestern Wisconsin have resulted in the build-up of P and to some extent, N, in soils. This build-up, combined with steep topography and upper and lower elevation farming (tiered farming), exacerbates problems associated with runoff and nutrient transport in these landscapes. Use of an at-grade stabilization structure (AGSS) as an additional conservation practice to contour strip cropping and no-tillage, proved to be successful in reducing organic and sediment bound N and P within an agricultural watershed located in the DA. The research site was designed as a paired watershed study, in which monitoring stations were installed on the perennial streams draining both control and treatment watersheds. Linear mixed effects statistics were used to determine significant changes in nutrient concentrations before and after installation of an AGSS. Results indicate a significant reduction in storm event total P (TP) concentrations (P = 0.01) within the agricultural watershed after installation of the AGSS, but not total dissolved P (P = 0.23). This indicates that the reduction in P concentration is that of the particulate form. Storm event organic N concentrations were also significantly reduced (P = 0.03) after the AGSS was installed. We conclude that AGSS was successful in reducing the organic and sediment bound N and P concentrations in runoff waters thus reducing their delivery to nearby surface waters.