Whole-herd optimization with the Cornell Net Carbohydrate and Protein System. III. Application of an optimization model to evaluate alternatives to reduce nitrogen and phosphorus mass balance

The objectives of this paper were to use a linear programming model previou sly described to evaluate different alternatives for reducing excess nutrie nts that may influence water quality on a case study farm (300 lactating co ws on 430 ha of cropland growing alfalfa, grass, and corn). Several alterna tives perceived to influence farm nutrient balance were evaluated for their potential to reduce N and P mass balance. Dividing lactating cow diets int o three groups according to their level of milk production versus a one-gro up total mixed ration decreased mass balance (tonne/yr) from 51.7 to 44.7 f or N, from 6.7 to 6.1 for P and from 16.2 to 14.8 for K with little influen ce on return over feed costs. Increasing forage quality (lower neutral dete rgent fiber and higher crude protein) did not improve N balance because of the increased N fixation from the air to the soil, but it increased returns over feed costs by $31,385. Improving yields to the maximum potential for the farm reduced mass balance by 29, 51, and 100% for N, P, and K, respecti vely, and increased returns over feed costs by $70,579. Changing the crop h ectare proportions to more corn and less alfalfa reduced N and K balances b y 19 and 29%, respectively, and increased returns over feed costs $39,383. Increasing annual milk production 10% by increasing milk production per hea d 10% compared with increasing animal numbers at the current average milk p roduction per cow until total milk increased 10% gave $34,132 more return o ver feed costs with less N, P, and K retained on the farm.