Micro-nutrient formulations should be applied only when a specific deficiency has been diagnosed. This technology was developed in the 1960s and became commercially available in the 1970s and 1980s. Price and availability of such formulations still restrict their use. Fertilizer quality is also a major concern but the development of new technology concerning nutrient release will help in sales of these types of fertilizer. These fertilizers have been used for centuries.
Animal manures are usually the best source of organic fertilizer.
Availability, transportation costs, and regulations limit widespread use of animal wastes in crop production. Relatively large quantities of animal manure must be applied to the soil to provide enough nutrients required for top yields, thus increasing the costs. Cover crops are used to improve soil physical properties, increase organic carbon, conserve soil water, reduce surface runoff, and recycle nutrients during heavy summer rains. Legumes are often used as cover crops as they also fix nitrogen in the soil. Composts have been increasing in popularity as soil organic amendments.