Conservation dairy farming impact on water quality in a karst watershed in northeastern US

One crucial challenge of agriculture is to increase productivity to feed the continuously growing population without deteriorating soil, water, and environmental quality. More emphasis on improved efficiencies, appropriate management of agricultural systems, and improved agronomic and nutrient use practices are needed to address this challenge. A conservation dairy farming system that produces the majority of the dairy feed and forage crops, with no-till, continuous diversified plant cover, and manure injection has recently been developed and tested in Pennsylvania, but the effect of this newly developed cropping system on nonpoint source pollution at the watershed scale is yet to be investigated. Topo-SWAT, a variation of the Soil and Water Assessment Tool (SWAT), was used to simulate nutrient and sediment loading processes of four dairy farming scenarios that differed in land area and implemented different feed production and nutrient input strategies: (i) forage crop production only and no best management practice (no-BMP scenario); (ii) forage production only and typical Pennsylvania management, which includes some no-till and cover cropping (typical scenario); (iii) forage and feed crop production with conservation management with broadcast manure (conservation-BM scenario); and (iv) forage and feed crop production with conservation management with injected manure (conservation-IM scenario). The conservation-IM scenario was the most effective for reducing total nutrient (42% N and 51% P) and sediment (41%) load in the watershed. The typical scenario also reduced nutrient and sediment load compared to the no-BMP scenario. Both conservation scenarios significantly reduced the number of in-stream peaks of organic N (73-82%), nitrate-N (43-47%), organic P (41-50%), and soluble P (62-70%) concentration compared to the typical scenario. Introduction of manure injection hindered runoff-mediated loss of nutrients but not leaching. Both conservation scenarios also decreased nitrous oxide emission by reducing denitrification. Additionally, manure injection retarded 91% of the N volatilization that occurred in manure broadcast scenario. The watershed scale study indicates that implementation of the conservation scenarios can largely contribute to the initiatives of achieving a target total maximum daily load in the Chesapeake Bay.