Nutrient Management in Soilless Culture in the Conflict of Plant, Microorganism, Consumer and Environmental Demands

Nowadays a trend in soilless cultivation systems is toward re-circulating and re-use of nutrient solution to avoid nutrient losses and to protect the environment. The standard strategy is the application of a nutrient solution based on empirical recipes and frequent analyses of the nutrient concentration in the solution. New concepts to predict nutrient and water uptake and thus supply are developed by several research groups. They are based mainly on growth and transpiration models and aim to synchronize nutrient uptake and supply related to yield. One of the remaining problems is the adaptation of the nutrient supply to climatic conditions. However, the larger present and future challenge is the nutrient management controlling further aspects of soilless production, particularly plant/microorganism interactions as well as taste and health related compounds in the product. The supply of silicon, phosphite, calcium, iron or other nutrients or nutrient like compounds may reduce the pathogenic activity in soilless systems. Regulation of pH and the control of the NO3/NH4 ratio can also have antipathogenic effects. On the other hand, antagonistic or plant growth promoting microorganisms can be fostered by a limited phosphorous supply (mycorrhizal fungi) or by a change of the composition (e. g., endophytes). Besides, appearance, taste and health related compounds determine produce quality. The improvement of taste by the increase of total sugars and soluble acids in tomato fruits is already a common practice. However, the use of different N-forms and the control of single nutrients, such as potassium, calcium, their ratio, and sulphate, can also influence quality related characteristics variously. This can affect even the allergenic potential or other nutraceutical properties of vegetables, not very much regarded yet. The consideration of microorganism and produce quality aspects often seems to counteract yield enhancement. Therefore, strategies are needed to optimize all aspects of nutrient supply, climate, and microorganism control to aim at an environmentally friendly and profitably grown produce of high quality. In the review examples from the research at the IGZ are presented indicating the conflict of plant, microorganism, consumer, and environmental demands and contributing to the search for an optimal crop management in soilless production.