Soil pH and Nutrient Availability
Our main goal in managing soil fertility is to assure an adequate supply of essential mineral nutrients for proper crop growth and development and ultimately for the production of high yield and fiber quality. Many of the nutrients described above are present in the soil in sufficient quantities to accomplish our objective. However, presence of a specific nutrient in the soil does not necessarily suggest availability to the plant. The key component to nutrient uptake is the chemical solubility of the ion that the plant requires and that solubility is highly dependent on soil solution pH. The following Figure illustrates the relative availability of nutrients as a function of soil pH. An illustrative example of this process is that of soil P dynamics in arid desert soils. Soil solution pH levels in desert soils may reach as high as 9 but are commonly near 8 to 8.5. At these pH levels most native soil P remains in an insoluble state.
In fact, applied P fertilizers that are soluble may revert to insoluble forms when it comes in contact with the soil. This is why banding applications of P fertilizer will help improve efficiency by minimizing the surface area contact with the soil. Programs aimed at managing pH in soils will help increase availability of native plant nutrients and improve the efficiency of applied nutrients through fertilizers. The addition of acid to alkaline soils and lime to acid soils will help to accomplish this. An accurate determination of soil fertility levels and pH will help to manage nutrients in an economically and environmentally efficient manner.