抄録
We analyzed the chemical characteristics of soils under protected cultivation. We applied a fertilizer which was modified with reduction of chemical stress, and showed the effect of the fertilizer on yield and fruit quality of tomato. 1 ) We collected 89 soils under protected cultivation from 7 prefectures (Saga, Yamaguchi, Kagawa, Aichi, Gifu, Shizuoka and Gunma) to estimate current soil chemical property in Japan. We determined the accumulated nutrients from residual fertilizer in soils in protected cultivation to be almost 6 times higher than those in open field cultivation. Although it has been said nitrate was most important residual anion, we showed that excess sulfate was also highly accumulated in the soil of protected cultivation. 2 ) We tried to use low-sulfate slow-release fertilizer (LSR) to control excessive nitrate and sulfate accumu1ation. LSR application made soil condition more correct. That is, LSR made soil pH more neutral and made soil EC low, mainly because residual sulfate was reduced. 3 ) These difference affected the fruit yield and fruit quality of tomato. During the three years' continuous cropping, the rate of blossom end rot (BER) was constantly suppressed using LSR (average BER rate : control 33%, LSR 23%). As far as yield is concerned, the third year yield for LSR application was 1.2 times superior to that for ordinal fertilizer application. 4 ) These differences were caused by chemical or water stress in rhizosphere. Bleeding rate of LSR application was faster than ordinal fertilizer application. this result suggests residual fertilizer reduced the transport of water and nutrient and affected yield and fruit quality of tomato.
