In contrast, nitrogen in other forms is only slowly available to plants. This is why only half the nitrogen from separated solids is available to plants during the growing season. Potassium from any of the sources is readily available to plants. Most of the phosphorus is available the season manure is applied. Sample and analyze manure from your dairy .
Nutrient content varies widely from farm to farm.
For example, Table 2 shows the low, average, and high nitrogen content of solids from 51 Willamette Valley separators. Nitrogen content varies almost sixfold from the low to high analysis. Value of manure Nitrogen generally is the limiting nutrient to plant growth and the most expensive to purchase. Phosphorus costs 20 cents per pound, and potassium costs 15 cents per pound. Figure 5 shows the annual fertilizer value of manure from 100 dairy cows.