Fertilization with Phosphorus, Potassium, and Other Nutrients

Phosphorus (P) and potassium (K) are primary macronutrients required in significant amounts by crops. Both are nonmobile in the soil since they are retained in the solid fraction and consequently, their management has some common characteristics. Most soil P and K are not available to plants. Reactions involved in their cycle in the soil imply that a significant fraction of applied P and K is not absorbed by the crop. P and K fertilizer management should minimize the transformation of applied nutrients to nonavailable forms and maximize crop absorption. To this end, banding or fertigation may be an alternative to broadcast applications. Management strategies for P and K should be designed in the medium and long term, contrasting with mobile nutrients such as N, whose management strategies are designed in the short term, i.e., for each growing season. The efficient use of P and K is gaining interest since both nutrients are nonrenewable resources, particularly P whose future scarcity will limit food security. Other nutrients are usually applied according to a sufficiency strategy, i.e., when deficiency is expected. Deficiencies in Ca and Mg are mostly likely in acidic soils. Mg deficiencies may be promoted by high Ca saturation in the exchange complex or by excessive K fertilization due to antagonism. The deficiency of micronutrients is not usually caused by a low soil concentration, but rather by soil properties that affect their solubility and the plant’s ability to mobilize, absorb, and transport these nutrients.