Soil tests attempt to assess the soil s ability to supply phosphorus from bound forms during the growing season. Like nitrogen, a relatively large proportion of plant-available potassium is taken up by crops each growing season. Plants deficient in potassium are unable to utilize nitrogen and water efficiently, and are more susceptible to disease. The slow release of potassium from native soil minerals can replenish some of the potassium lost by crop removal and leaching. This ability, however, is limited and variable.
Fertilization is often necessary to maintain optimum yields.
Sufficient calcium must also be present in actively growing plant parts, especially storage organs such as fruits and roots. Properly limed soils with a constant and adequate moisture will normally supply sufficient calcium to plants. High humidity and poor soil drainage hinder calcium movement into these plant parts and should be avoided. Like Calcium, Magnesium is ordinarily supplied through liming. Micronutrients - The micronutrients are elements essential to plants, but required in very small amounts.