The response of plant and soil fertility

Soil fertility is the ability of the soil to supply all the necessary nutrients required for optimum yield of plant. Soil test is the most practical way of ascertaining the proper measurement of the nutrient supplying power of the soil and indicating if fertilizer or limes are needed in the soil. Fertilizers are applied to soil to supply essential nutrients that may be inadequate in supply or unavailable to plants from the soil. Plants absorb nutrients from the soil and use them to produce new growth or crop. The application of agricultural fertilizers has greatly increased crop yields over the past years by eliminating nutrient availability as a major limitation to yield. When a particular nutrient is inadequate in supply, application of additional nutrient will then increase growth and yields. Initially this may be a linear response where yield increases one unit per unit of fertilizer added. At some point the response levels out and yield increases become less pronounced as additional fertilizer is applied. This is followed by a plateau where yield is not increased with additional applications of nutrients.

However, plants may continue to absorb nutrients without having a corresponding increase in yields. This is the case of luxury consumption. At the far end of the plateau there is a point where excessive nutrient levels is found, especially micronutrients, may become toxic to plants and will reduce plant yields. The goal in applying fertilizer is to supply enough nutrients to provide optimal plant growth without supplying too much fertilizer to the soil.