Managing nitrogen on dairy farms: An integrated approach .1. Model description

Nitrogen management on dairy farms can be enhanced with integrated and quantified information about N flow through various components of the system. A computer worksheet was developed to integrate several aspects of farm management, including ration formulation, crop selection, and manure application. Nutritional requirements of cows were determined from milk production, growth, and maintenance, and diets were formulated to meet these requirements based on the Cornell Net Carbohydrate and Protein System. Annual manure production and fractionation of feces and urine were calculated based on the N balance in the herd and external sources (i.e., bedding and wash water). The availability of manure N and the field history of soil and crop management assisted in the determination of crop N fertilization. Manipulating dietary formulations to meet herd nutritional requirements with less dietary N can be helpful to optimize feed selection and reduce manure N excretion simultaneously. Aggregated annual feed requirements of the herd foster the development of cropping and feeding strategies. The worksheet largely was empirically based, simple to use, and adaptable to any size dairy farm. The model was used to compare efficiencies of N utilization and balances of inputs and outputs with different management strategies and was demonstrated to be a useful planning tool for N management to minimize potential N losses to the environment.