Topographic wetness guided dairy manure applications to reduce stream nutrient loads in Central New York, USA

Abstract Study region Fall Creek Watershed in central New York, USA. Study focus Dairy manure is commonly applied to NY, USA agricultural fields as both a crop nutrient source as well as a means of waste disposal. Managing excess manure places an economic burden on small farm operations due the prohibitive cost of existing practices and regional dominance of saturation-excess hydrology. Through a SWAT modeling exercise we evaluate the efficacy of dairy manure application following the topographic wetness index (TI) as a means of reducing non-point source agricultural nutrient runoff. Next, we examine the efficacy of amending dairy manure with chemical N as a means of reducing the rate of soil TDP accumulation. New hydrological insights We observed that application of manure to drier pastures results in less TDP and NO X surface losses, but an undesirable increase soil TDP accumulation. Further, pastures receiving dairy manure are typically N limited during summer months, limiting plant P uptake. Manure N amendment reduced TDP accumulation and increases crop yield, but slightly increased NO X surface losses. Spreading dairy manure based on the TI concept represents a feasible path towards reduction of agricultural non-point nutrient runoff, although management strategies need to consider ways to also reduce the long-term accumulation of soil P, which could have consequences in the future that are difficult to mitigate.