Hydroponically grown leek: slowly growing to maturity

Leek traditionally grows in a sandy soil in the open field in The Netherlands. However, the vulnerability of sandy soils to leaching of nutrients to ground- and surface water is high. Therefore leek was chosen for experiments to be grown out of the soil in the open field. Investigations took place to certain aspects of system development which were reported in 2011. During the following years the research focused on commercializing the design (supporting tubes in floating panels in a DFT system), upscaling the system to several ponds of 200 m2, marketing the product, solving specific problems which appear during those experiments (oxygen content of the nutrient solution, continuous circulation, virus symptoms) and economic aspects. The semi-commercial system developed was based on various trials at which a plant density of more than 70 plants m -2 is needed to achieve plants of more than 200 g which are thicker than 2.0 cm. Hydroponically grown leek should be graded before planting on the panels. Fast growing cultivars should be chosen year round. Uniform planting material is needed for a uniform, single date, harvest. The age of the plant is of less importance for the quality of the harvested product. This gives flexibility in the planting date which often depends on the harvesting date of the former crop and, consequently the weather before. Besides the plants should be >20 g to be planted in the 20 cm long tubes, otherwise the growth is delayed (no catchment of light inside the tube). The cultivation period was similar to earlier trials (50-75 d). The taste of hydroponically grown leek was comparable with leeks raised in soil. During cultivation, symptoms of the yellow stripe virus were seen more frequent compared to soil grown leek. Reuse of the nutrient solution during 4 crops a year saves about 50% of the fertilizers required. Another aspect of importance in The Netherlands is the surplus of rainfall (800 mm average year-1) during the growing season compared to the water uptake (300-500 mm). Adaptation of the system or discharge strategy was investigated Hydroponically grown leek slowly grows to a mature cultivation system by solving the topics mentioned-above, therefor it can be used by commercial growers now. The importance of a slow upscale was proven by the appearance of several unforeseen aspects (oxygen, rainfall, duration of irrigation), while in marketing a first step is taken to bring hydroponically grown leek as a distinguishable product.