Soil nutrient dynamics and plant-induced nutrient mobilisation in organic and low-input farming systems: conceptual framework and relevance

ABSTRACT Plant nutrition practice in organic agricultural systems is sometimes reduced to a renunciation of applying readily soluble mineral fertilisers. In organic farming, however, soil nutrient stocks are regarded as an additional source of plant-available nutrients that can be mobilised by crop plants through rhizosphere effects. Therefore, unlike in conventional farming, the focus is not on replacement of the nutrients removed by the harvested products through readily soluble fertilisers enhancing nutrient concentrations in the soil solution. Instead, it is on minimising nutrient losses and supplying plant nutrients through soil-plant-microorganism interactions in which improved soil structure and enhanced soil biological activity facilitate plant-induced nutrient mobilisation and nutrient uptake under conditions of limited nutrient availability in the soil. This paper reviews these soil processes that improve the availability of macro- and micronutrients to plant roots under conditions of limited nutrient availability. It focuses on providing a conceptual framework for the different processes contributing to nutrient mobilisation and within which the various strategies for improving nutrient efficiency can be integrated in organically managed soils. Essential farm management options based on scientific views of nutrient dynamics to maintain soil fertility are addressed. With diverse, legume-based crop rotations with an adequate proportion of time dedicated to fertility building crops, careful management of manure and organic residues, and by using permitted inputs for phosphorus (P) and potassium (K), organic farms can be managed sustainably. However, efforts for recycling nutrients, mainly phosphorus, need to be enhanced.