Environmental and economic optimization of dairy manure management: A mathematical programming approach

Manure allocation on dairy farms to meet crop nutrient requirements, minimize environmental risks of nutrient loss, and maximize economic returns is a complex management decision. A multiple-criteria, mathematical programming approach was developed to assess decision-making with respect to manure allocation decisions at the farm scale. The objective function to be optimized includes several subfunctions developed for considering economic and environmental indicators, such as the Phosphorus Site Index. The structure of the nonlinear model allows the planner to change the importance among subfunctions, making it possible to obtain solutions that meet different management objectives for manure allocation. Optimization results for a New York State dairy farm were compared with recommendations made by a farm planner. The results show that using this optimization model allowed the total amount of manure within the farm to be applied, satisfying the nutrient requirements and keeping the P-Index low in all fields where manure was applied. The optimized recommendation resulted in a 31% reduction in the average P-Index weighted by field area and in a 50% reduction in the standard deviation of the P-Index among fields, mainly because manure application was minimized in fields with higher soil-test P and with higher P transport factor. This approach is a definite improvement over current practices used in nutrient management planning, but due to difficulties associated with nonlinear programming, this software is not easily adapted for general use.