Nutrient Use in Grazed Dairy Systems--Implications for Nutrient Management Planning.

In grazing-based dairy operations, the majority of dry matter intake is derived from pasture grazing by cows. While there is an increasing reliance on imported feed such as grain-based concentrates and hay, feed quality and nutrient content varies throughout the year. Additionally the redistribution of manure nutrients in the landscape is largely from direct deposition by animals. As a result of grazing, feeding and forage harvesting practices, cow numbers and time spent in various locations vary across the farm. The resultant uneven distribution of manure nutrients present unique challenges and may pose high risks of nutrient loss and environmental contamination in some areas. Nutrient management planning in grazed dairy operations has previously focused on achieving greater productivity through the strategic use of fertilizer, but more recently has also included farm-gate nutrient balances and nutrient-loss risk assessment. There is further scope to improve nutrient management planning by better defining relationships between feed nutrients and nutrients in milk and excreta, and better quantifying manure nutrient loads at the paddock scale through the inclusion of spatial and temporal information about cow movements. This presentation will discuss current and future nutrient management challenges facing grazing-based dairy operations and propose on-farm measures to improve nutrient use efficiency.