A Model of the Whole Farm System

The model demonstrates that nutrients enter the farm as imported feed, legume fixed nitrogen from the atmosphere, fertilizer purchases, or imported manure. From here, they are cycled through the system until they are lost. The ways that nutrients are lost from the farm include production and export of milk or meat, or losses from manure or soil from volatilization, runoff, leaching or denitrification.

Improving nutrient utilization in any subsystem will reduce nutrient losses from the farm. For example, improving nutrient utilization in the animal can reduce the amount of manure nutrients produced. Thus, when manure is applied and the unavoidable losses occur, these losses will be reduced proportionately. In addition, less feed nutrients will be required. Therefore, the associated losses from crop production will also be reduced.

Improving the utilization of nutrients by the animal is the most effective way to reduce nutrient losses from the farm. However, animal feeding is also related to crop selection, and crop selection affects nutrient losses. Additional savings (financial and environmental) can be obtained with better manure application methods.

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