Determining Optimal Nutrient Management Strategies for Dairy Farms

A model for dairy nutrient management was constructed to evaluate strategies for nutrient recycling using farmspecific information.The model used linear programming to determine optimal cropping systems that used nutrients from dairy manure applied to cropland.The optimal system minimized total feed costs, including purchased commodities, based on the ability of crops to take up manure nutrients and supply forages for cow rations.Nutrient uptake requirements to meet mandated regulations were incorporated as constraints to the linear programming model and were for either N or P.Results from sensitivity analyses showed that rations balanced for maximum DMI versus solutions with less than maximum DMI affected the crops used in the optimal cropping system and increased feed costs.The effect was greater on feed costs at low production than at high production.The value of additional acreage was lower with no minimum requirement on DMI.Winter was the limiting season for N and P recycling because of less uptake by crops.Feed costs were almost always lowered by increasing crop acreage be- yond the minimum required for N recycling.