Nutrient managements in soil

Agricultural practices of adding mineral nutrients to a soil at a crop site have taken many forms. Perhaps the most common is the long rotation method best described as slash and burn cultivation. In the many variations of this practice slow growing vegetation is allowed to grow, unharvested, for several years and then nutrients are converted into a plant available from by fire. This practice essentially “mines” the total elemental reservoirs in that particular soil and and although I have seen no data, it seems reasonable to conclude that dictated by the total elemental content of the root zone.

Use of animal manures to augment mineral nutrition at a selected crop site is also a common practice. However, such practices rely on the animal ingesting nutrients via vegetation harvest at another site and concentrating those nutrients on the selected site. Clearly, this practice can only succeed in a global sense if all the refuse from the cities of the world are recycled to crop sites. At present the high cost of transporting these very diluted nutrient sources and the extreme concentration of food consumption in cities limit adoption.

Perhaps the most common practice in replacing soil mineral derived nutrients at a crop growing site is the importation of concentrated, highly soluble forms of the elements in the form of mineral fertilizers. Adoption of soluble mineral fertilizers depends upon many factors not the least of which is the natural fertility of individual kinds of soil.

Clearly the soil resource, in toto, has to have help in supplying those nutrients of mineral origin, especially P and ultimately K, Ca, and Mg if food is going to be harvested and consumed at another site. Whereas temperature, water and nitrogen contents in the soil are restored by atmospheric sources, no such nonmineral source is available for the mineral derived elements. Technologies that only allow crop plants to obtain larger portions, so called available forms, of these elements are at best delaying actions. Deep rooting to enlarge the volume of soil from which these elements can be extracted only offers a similar scenario.