Abstract
In a drip-application (fertigation) culture, plant nutrients are supplied both from nutrient solution and from soil media. The objective of this study was to determine whether the nutrients such as phosphorus or bases should be added in the solution or to the soil. Melon and tomato plants were successively cultivated with drip-application of nitrogen solution or mixed nutrient (N, P, K, Mg, Ca) solution. Before each transplanting, the soil was tested for phosphorus and bases, and supplemented with liming materials, potassium, and phosphorus aiming at 80% of base saturation and 300 mg kg^<-1> of Truog-P_2O_5. Those targets are the standard level of soil chemical improvement, but less than recent soil amounts for greenhouse culture in Japan. 1) Melon and tomato growth was affected strongly by application of nutrient solution. Regardless of soil chemical improvement, their harvest and the absorption of P and K were higher in the mixed nutrition treatment than in the nitrogen treatment. When nitrogen solution was applied in the chemically improved plots, plant harvests were as high as in the control plot (conventional soil culture). However, the absorption of nutrients, particularly of potassium, decreased markedly in the later stage of cultivation. When nitrogen solution was applied in the non-improved plots, plant harvests and sugar contents were too low. 2) The roots of plants were concentrated in the soil near emitters of drip tubes, and were few between plant hills. Contents of bases in the soil after cultivation were decreased in the vicinities of the emitters but not much changed between plants. These findings suggest that in drip-application culture, the nutrients like P and K which are not very mobile in soil media, should be applied in the solution, rather than applied uniformly in the soil media. 3) In this experiment the addition of magnesium and calcium to the solution was not so effective. The plant growth depended so strongly on potassium application, that magnesium and calcium may have affected antagonistically the absorption of potassium, when they were added to the solution. 4) Soil chemical improvement affected plant growth and yield. Therefore, it is considered that soil analysis and diagnosis are important even in a drip-application culture.
