INFLUENCES OF HEAVY APPLICATION OF NITROG EN ON SOIL ACIDIFICATION AND ROOT GROWTH IN TEA FIELDS

We surveyed the actual levels of nitrogen application in the productiv e region of green tea in northern Mie prefecture and investigated the physico-chemical properties of the soils and root growth in the tea fi elds. The annual quantity of nitrogen supplied ranged from 5.8 to 28.3 kg a(-1), giving 14.7kg a(-1) on average. The annual quantities of pho sphoric acid and potassium were 5.7 and 4.6kg a(-1) on average, respec tively. More than 20kg a(-1) of nitrogen had been applied annually for 11% of the surveyed tea fields. White roots in the topmost layer (0 s imilar to 20cm) of inter-row soil were considerably reduced when nitro gen exceeding 14.0kg a(-1) was applied and were not found when the amo unt of nitrogen exceeded 18.0kg a(-1). The soil acidity (H2O) in the i nter-row decreased from pH 5.9 to 2.9 with an increase in the amount o f nitrogen applied. The topmost layer of inter-row soil was highly aci dic lower than pH 4.5. Anions in the soil solution collected in the in ter-row were mainly composed of NO3- and SO42- and the concentration o f anions exceeded that of cations. The soil acidity was kept at pH 3 w hen alminium inos were available to compensate for the lack of cations .