These processes are important because most plants are only able to take up certain chemical forms of each nutrient. Therefore, many of the soil processes can make the nutrient elements unavailable or slowly available for plant uptake. While each nutrient element may differ in the transformations it undergoes, some important common processes are listed below. An understanding of these processes may aid in better management of fertilizer and other nutrient sources. The largest source of nutrients in most unfertilized soils is contained in organic compounds.
Organic compounds are generally different from inorganic compounds because they contain carbon.
Mineralization is the process by which organic nutrients are converted to inorganic forms which plants can take up. Frequently, the addition of woody materials without added N fertilizer can result in short-term N deficiency in plants. The general rule is that organic materials with an organic carbon to N ratio of greater than 30 will cause N immobilization. Addition of supplemental fertilizer N or an organic material with a high proportion of N can reduce the risk of N immobilization in the soil. The surfaces of small clay or organic particles often have a net negative charge on them.