Overview of developments in recirculation of drainage solution for crops in soilless production systems

Cropping systems with growing media offer the technical possibility to collect and re-use drainage solution as well as all nutrients in the drainage solution. Recirculation makes it possible for most places on earth to increase water use efficiency with 30%, and nutrient use efficiency with over 50%. It will be argued that drainage solution is affected by the natural property of plant roots to take in some elements more readily than others. Furthermore, when recirculating, the amount of nutrients added to the system must carefully match the amount of nutrients leaving the system, by plant uptake and unavoidable losses, otherwise accumulation or depletion of one or more elements will occur. A brief history of nutrient recommendation systems and of a version currently in use in the Netherlands will be discussed. Practical problems and current solutions will be shown for 1) disinfection; 2) various water qualities; 3) accumulation and management of sodium; 4) the unequal distribution of irrigation solution in supply pipes; 5) dealing with fluctuations in both the amount of drainage solution and the amount of nutrients with a nutrient recommendation system; 6) ion specific meters; and 7) balance registration. The consequences of new developments will be discussed with suggested lines of research.