Applying nitrogen (and/or other nutrients) through the irrigation system during cultivation is called fertigation. The system offers a means to adjust the supply of N to the nutritional need of the crop, thus limiting NO3 leaching and luxury consumption of N, which in leafy vegetables can lead to unacceptably high NO3 contents. In the following, fertigation is compared with broadcast dressing, up till now the usual practice in the Netherlands in open-air cropping. Conditions for a successful fertigation system are (Goldberg, 1976; Bucks et al., 1982): soluble fertilizers, if possible with minimum corrosive effects, good water quality: sand or undissolved particles can block tubes and/or emitters of sprinkler/trickle-irrigation systems. Ca and Mg or Fe may precipitate if the pH of the water is too high. Activity of micro-organisms in tubes and emitters or drippers must be prevented, a distribution system with storage facilities for water and concentrated nutrient solution, distribution tubes to sprinklers or drippers, a control system (EC, nutrient concentration), time switches, etc. for automatic operation of pumps and for control of fertigation. Modern materials and techniques are available to develop an efficient system and most Dutch vegetable growers already have a more or less automatic system for distributing water in dry periods.