Organic greenhouse production in Europe, the challenges of sustainable management of the root environment

Field: Agricultural and Biological Sciences (Life Sciences)

Until about fifteen years ago, organic greenhouse horticulture in the Netherlands and Western Europe was limited to a handful of growers with small non- or only limited heated greenhouses. Since then the area rapidly expanded and have reached an area of about 150 ha. This expansion was driven by the increasing demand in the late 90’s and early 2000’s. The area grew faster than the number of growers, since some large nurseries with fruit vegetables converted from conventional to organic growing as well some existing organic growers expanded their area significantly. Conversion to organic greenhouse production is rather straightforward at one hand because conventional production is already virtually pesticide free, however on the other hand some major other obstacles will appear. More than in other agricultural sectors, organic greenhouse horticulture has to find compromises between the use of modern technology as in the state of the art greenhouse technology at one hand and the viewpoint and attitude from the side of organic production on the other. Within the EU organic agriculture is strictly legalized (EU 2091/92), however many aspect of modern greenhouse horticulture are not covered with this regulation. The platform of growers and retailers therefore agreed upon additional guidelines which were in line with the viewpoint of organic agriculture. The main aspects are exclusion of additional artificial lighting and substrate growing and a limitation in energy use. Therefore high product prices are crucial for the viability of organic greenhouse production as the production costs are higher than those for conventional greenhouses, moreover the total yield is often significantly lower than in conventional crops. Stimulated by the European Action Plan on Organic Farming, the Dutch Government promoted the transition to- and the development of organic horticulture among other things by additional research funds. As a results, projects were initiated aiming at improvement of organic greenhouse production methods towards robustness and sustainability. Since organic production is limited by its own philosophy and principles, among them many restrictions concerning the soil and fertilizers, major bottlenecks in organic farming are soil related. Important problems are the limitations on the use of manure with regard to the N or the P quantity, the unbalanced input of nutrients inherent to organic fertilizers, the restrictions on irrigation and consequently increased salinity problems. Moreover, crop rotation ordained as a fundamental principle of sustainable organic agriculture is a major obstacle, since the number of economically viable crops is very limited. On top of that, legal targets restricting N and P inputs are effective for greenhouse production in general. In view of this, in research projects emphasis was laid primarily on organic matter management to optimize the nutrient balance at one hand and improve disease resistance of the soil system on the other. In this contribution the research on water and nutrients of the last 10 years will be evaluated. Firstly an evaluation was made on water- and mineral balances. A database of organic fertilizers and soil improvers with relevant parameters was developed, based on existing data and filling in the gaps by additional tests. A decision support model for growers was developed combining the database with existing models on N-dynamics (mineralization, denitrification), crop nutrient demands and the water balance of crops and soil. At the same time experiments were performed at individual growers, varying organic fertilizer inputs, or strategies of irrigation and base- and top dressings, to validate the database and the models and demonstrate the use. All activities were performed in close cooperation with the group of organic greenhouse growers, extension service and the research institutes. The projects resulted in applicable guidelines with regard to irrigation and fertilization practices for organic greenhouse production, to meet the targets for both the organic production itself and the legal effective targets for N and P input. However, facing the impending targets on N and P emission and the problems with crop rotation and soil-borne diseases, a lot of work lays ahead.