Water and mineral balances of organically grown vegetables under glass

Water and mineral inputs and outputs were observed for two years at five glasshouse holdings with organically grown vegetables. Large differences in the quantity of water irrigated were found between the holdings that did not coincide with estimations of evapotranspiration. At two holdings the estimated leaching of nutrients was high and large differences were found in mineral content of organic fertilizers. At two other holdings with sandy soils, high NO3 concentrations were found in the soil solution 100 cm below the soil surface, resulting in an estimated loss of 40 and 470 kg N ha(-1) yr(-1) respectively. However, at a further two holdings with clay soils and high ground water levels, NO3 levels were low resulting in an estimated leaching of below 10 kg N ha(-1) yr(-1). Irrespective of the P-buffer in the soil, the P input exceeded the legislative quantity by up to two- to five-fold.