Improving the nutrient status of a commercial dairy farm: An integrated approach

Minimizing nutrient surpluses and improving efficiency of nutrient use are key challenges for all dairy farming production systems, driven by economic, environmental and increasing regulatory constraints. Our study examined the efficiency of N, P and K use on a commercial dairy farm through an integrated approach that evaluated the nutrient status of all aspects of the production system of the case-study farm, a 75 lactating Holstein cow dairy in Kings County, Nova Scotia, Canada. During the decade after 1988, the farm owner implemented a series of changes in production practices, including diversification of the crop rotation, implementation of a management intensive grazing (MIG) regime and adoption of a systematic approach to soil and nutrient management. Milk production, and associated farm exports of N, P and K, increased by 666 kg cow−1 between 1990 and 2000. Purchases of N-P-K fertilizers were eliminated in 1990 and feed nutrient imports were dramatically reduced. Feed costs per liter of milk declined from 14.3 cents (CDN) liter−1 in 1990–92 to 11.6 cents liter−1 in 1998–2000, even as feed prices increased regionally by 10–20% over the same period. Modeling of current whole farm mass N, P and K balance indicated that 25.0% of all N inputs are recovered inform products, milk and meat. Non-legume-derived field N input (67kg Nha−1 before losses) was close to optimum for the predominantly legume/grass-based forage cropping system. Model-determined annual farm nutrient surpluses (outputs-inputs) for P (9.0kgha−1 yr−1) and K (8.2 kg ha−1 yr−1) were significantly lower than those previously reported for regional confinement-based dairy farms, which were more reliant on corn production. However, data from 16 years of soil analysis (1985–2001) indicated an increase in soil-test P levels of approximately 2 mg kg−1 yr−1. Recent refinements in dairy animal dietary P levels have further reduced the farm P surplus (2.6 kg ha−1 in year 2001) and are shown as key to a strategy for reversal of the trend in soil-test P levels. In summary, the combined approach of whole-farm system nutrient management, crop diversification and MIG increased milk production and minimized costs while reducing farm nutrient inputs. The study demonstrates how an approach to dairy farm nutrient management which integrates livestock and crop nutrient requirements may reduce dairy farm nutrient loading while maintaining productivity.