This report documents results from a six-year study (1996-2001) that evaluated effects of liquid swine manure application management practices on soil nutrients, organic matter, pH, crop yield; and also discussed water quality implications. Swine manure management practices included single-rate (SR) and double-rate (DR) nitrogen (N)-based application rates (168 and 336 kg N ha-1, respectively), three timings (fall injection [FI], winter broadcast [WB], and spring injection [SI]), and two methods (broadcast and injection) of liquid swine manure. Analysis of these practices involved comparing levels of residual soil total phosphorus (P) as Bray-1 available P (RSP), residual soil nitrate-N (RSN), percent organic matter (OM%), pH, carbon:nitrogen (C:N) ratio, and crop yields (kg ha-1) in a corn-soybean rotation. Results of this study indicated that long-term application of higher liquid swine manure rates during winter and spring application times resulted in significantly higher post-harvest accumulation of RSN and RSP in the soil profile, with no significant changes in soil OM%, pH, and C:N ratio. These results also showed that incorporation of swine manure during the spring application time produced significantly higher corn yields compared with fall and winter application times. Overall results suggest that while RSN and RSP content may be significantly higher from spring versus fall manure application times, N and P runoff losses and the potential threat to surface water quality may be substantially lower during spring and summer compared with fall and winter due to effects from crop nutrient uptake, microbial activity, leaching, and evapotranspiration during the growing season.
Available at: http://works.bepress.com/rskanwar/84/