The values shown in table 4 indicate average expected nitrogen available to plants after denitrification losses. Once below the root zone, this nitrate is a potential ground water pollutant. Again, soil type and rainfall are the major influencing factors. Soil permeability can range from less than 0.06 inch per hour for clay soils to greater than 20 inches per hour for gravelly sandy soils. The nitrogen bound by the microorganisms will become available to the plant, but it will take a longer time.
Inorganic nitrogen is the form that is taken up by the plant root system and used for growth.
The organically bound nitrogen in the soil breaks down with time to form inorganic nitrogen. With enough time, the organic nitrogen present in manure will be converted to plant-usable inorganic nitrogen. This means that a fraction of the added manure won't be available for plant uptake. This nonavailable fraction is sometimes referred to as the recalcitrant fraction. This fraction won't add to surface or ground water pollution problems.