Growth, Yield, and Mineral Salt Contents of Radish Plants Grown Hydroponically with the Quantitative Management Method

摘要

In the quantitative nutrient management (QNM) method supplying a whole amount of nutrients needed for vegetable production in hydroponics at the beginning of cultivation, plants are cultivated under the conditions of high salt concentration during theearly growing stage. To make clear the effects of these conditions on growth and mineral content of radishes, radishes were grown hydroponically with three different concentrations of medium solution. Nitrate salts supplemented with a small amount of NH_4~+ (NSA-treatment) or nitrate salts alone (N-treatment) were supplied as nitrogen sources. The pH in N-treatment increased during the cultivation, with the increase being diminished by NH_4 -N supplementation. The quantitative growth analyses showed that dry weight growth was not significantly promoted by the NH_4~+ -N supplementation or higher concentration of nutrient solution, whereas leaf elongation was stimulated. It appeared likely that N and K content were particularly important factors affected by the medium concentration. However, significant effects of the different medium concentration were not observed in N and K content (mg/plant, mg/100 mg DW) during the early growing stage, whereas these contents (mg/plant) were strongly affected by the medium concentration at harvest. From these results, it became evident that growth and mineral content was unaffected by the medium concentrations during the early growing stage. These facts were suggested to explain a part of reasons why radish yieldis almost unaffected by the hydroponic culture with the QNM method. Furthermore, the supplementation of a small amount of NH4 to the medium containing NO3 as a major nitrogen source was available for reducing the changes in medium pH even in hydroponic culture of radishes with the QNM method.