Some nutrients, such as nitrogen and phosphorus, are present in the soil in large amounts but are made available to plants only very slowly. Others, such as potassium, are both present in the soil in large amounts and readily available.
Nutrients also behave differently in the soil.
One important behavior characteristic of a nutrient in soil is its relative mobility. This is illustrated in Figure 2-2. In general, as nutrient mobility increases, fertilizer placement becomes less critical but the potential for nutrient loss becomes greater. Thus, nitrogen placement relative to the plant is not very critical for uptake, but the potential for loss of nitrogen once it has been applied to the soil generally is very high, and little available nitrogen will accumulate in the soil. Conversely, as nutrient mobility decreases, fertilizer placement becomes more critical, but the potential for nutrient loss lessens.