Fertilizer source and soil aeration effects on runoff volume and quality

Minimizing runoff losses from grasslands may benefit the producer and abate potential eutrophication of aquatic systems. This study was conducted to evaluate the effects of fertilizer source and soil aeration on the volume and quality of runoff from grassed plots. Sixteen tall fescue [Festuca arundinacea Schreb.]-bermudagrass [Cynodon dactylon L.] plots were established on Altavista sandy-loam soil (fine-loamy, mixed, semiactive, thermic Aquic Hapludults) in Georgia, USA. Two fertilizer sources (inorganic fertilizer [IF] and broiler litter [BL]) and two aeration treatments (aerated and nonaerated) were factorially combined to generate four experimental treatments. Broiler litter was applied at 1765 kg dry matter ha(-1) and IF was applied to match nutrient rates applied with BL (36 kg available N ha(-1), 39 kg P ha(-1), 60 kg K ha(-1)). Simulated rainfall was applied immediately after fertilizer application and 1 mo later. Runoff samples were analyzed for dissolved reactive phosphorus (DRP), total Kieldahl phosphorus (TKP), and ammonium (NH4-N). In the first runoff event, plots fertilized with IF lost more TKP than plots fertilized with BL (3.4 vs. 1.1 kg P ha(-1)). In contrast, plots fertilized with BL lost more NH4-N than plots fertilized with IF (1.4 vs. 0.6 kg N ha(-1)). These results support the use of different weighting factors for BL and IF when assessing their potential for contaminating surface runoff. Aeration numerically reduced runoff volume by 27%, though not significantly, in the first runoff event (P = 0.16), but did not affect runoff volume 1 mo later. Aeration did not affect the mass losses of DRP, TKN, and NH4-N. These results indicate that aeration or bayed grasslands on these soils would not he expected to significantly affect the volume and quality of surface runoff.