Management effects on nitrogen and phosphorus losses in runoff on expansive clay soils

Raised wide beds have been proposed as a conservation tillage practice for reducing erosion losses in vertisols, but few measurements of nitrogen (N) and phosphorus (P) losses have been reported. The objective of this study was to examine the impact of tillage systems and fertilizer N application methods on sediment and nutrient losses associated with interrill runoff. Simulated rainfall events (125 mm h(-1) until 30 min of runoff had occurred) were applied to raised wide beds (0.15 m high and 1.5 m wide with 0.5-m-wide furrows) on a Houston Black clay (fine, montmorillonitic, thermic Udic Pellusterts) which had been managed with either a no-till or a chisel-till tillage system. Three simulated methods of applying fertilizer N (surface band, coulter-nozzle, or spoke wheel simulated field practices) were compared in a split plot experimental design with four replications. Total N and P losses, as well as fertilizer N losses, in both sediment and solution from interrill runoff were determined from 1 m(2) plots. While no P was applied in fertilizer, greater P losses were observed with the chisel-till compared to no-till. While N losses in runoff were relatively low, fertilizer N application with surface banding or the coulter-nozzle applicator in no-till had greater total N and fertilizer N losses. Under relatively wet soil water conditions, respective losses of total inorganic N and fertilizer N in solution were greater from no-till with 4.0 and 2.0 kg N ha(-1) lost, as compared to 0.2 and 0.1 kg N ha(-1) lost from chisel-till per rainfall event. Losses of N in sediment were greatest in chisel-till, with 2.1 and 0.03 kg N ha(-1) lost from chisel-till, as compared to 0.6 and 0.01 kg N ha(-1) lost from no-till, of total N and fertilizer N per rainfall event, respectively The greatest N losses during the runoff event was observed with the surface banded and coulter-nozzle fertilizer application methods in no-till due to increased fertilizer N losses.