There was a time not long ago when agronomists were convinced that the only nutrients a plant needed were nitrogen, phosphorus, potassium and a few minor elements. However, research has since confirmed that proper plant nutrition requires a complex interaction of nutrients and trace minerals in order to promote the formation of organic acids capable of sustaining an active micro-biological system in the soil. It is the soil's microbial populations that perform nearly all the critical functions vital to the growth of a plant: Nitrogen fixation, soil aggregation, oxygen and carbon dioxide release, mineral conversion, translocation of nutrients in plant tissue and photosphere protection of the root system. It is the indigenous micro-organisms that process nutrients to create humus. Humus acts like a sponge that retains moisture and nutrients within the root zone of the plant. Moreover, soil rich in humus protects the root system by buffering salts, nitrates, and other toxins that have accumulated following years of fertilizer and pesticide applications.