Nutrient Supply in Organic Agriculture – Plant Availability, Sources and Recycling

Abstract

This chapter examines the practice of applying nutrients in organic or slowly soluble inorganic form in the belief that plants will obtain balanced nutrition through the actions of soil microbes. The organic principle of only fertilising the soil and not directly feeding the crop with water-soluble nutrients has no support in science. The release of organically bound nutrients in soil through biological activity is not necessarily synchronised with crop demands and occurs even at times when there is no crop growth. Changes in the soil biological community do not overcome this limitation. Despite the ideal of organic agriculture being self-sustaining through cycling of nutrients, in principle only on-farm wastes are recycled and most municipal wastes are excluded due to concerns about pollutants and philosophical views on life (biodynamic agriculture). Nutrient supply in European organic agriculture is mainly covered through purchase of straw, manure and fodder from conventional agriculture and by-products from the food industry. Untreated minerals seem to play a minor role. The fertility of agricultural soils can only be maintained over the long-term if plant nutrients removed are replaced with equivalent amounts and if added sources have a higher solubility than those present in the soil. These conditions are in most cases not fulfilled in organic agriculture. It can thus be concluded that the naturalness of nutrient sources is no guarantee of superior quality and that promotion of organic principles does not improve the supply and recycling of nutrients but excludes other more effective solutions for nutrient use in agricultural systems.