What you need is determined by realistic personal assessment of a farming operation. It is not possible to underestimate the value of record-keeping in nutrient management. Yield history and management level should provide a reasonable starting point to project future yields. With realistic yield goals, it is possible, using resources available from farm advisors, to estimate nutrient requirements of any future crop. It is important to make the difference between nutrient uptake and removal.
Plants utilize nutrients throughout their entire system from the roots to the pollen.
This is not all removed by crop harvest and remains in the field. Another consideration in nutrient removal is the mode of harvest. For example, most forage crops have substantial quantities of K in the leaves and stems, thus K fertility must be monitored closely when hay is harvested and hauled from the field. It is simple to illustrate these points with one example. When applying chicken litter near a small stream, simply drive far enough away from the water that no litter goes into it.