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

We surveyed the actual levels of nitrogen application in the productive region of green tea in northern Mie prefecture and investigated the physico-chemical properties of the soils and root growth in the tea fields. The annual quantity of nitrogen supplied ranged from 5.8 to 28.3kg a(-1), giving 14.7kg a(-1) on average. The annual quantities of phosphoric acid and potassium were 5.7 and 4.6kg a(-1) on average, respectively. 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 similar to 20cm) of inter-row soil were considerably reduced when nitrogen exceeding 14.0kg a(-1) was applied and were not found when the amount of nitrogen exceeded 18.0kg a(-1). The soil acidity (H2O) in the inter-row decreased from pH 5.9 to 2.9 with an increase in the amount of nitrogen applied. The topmost layer of inter-row soil was highly acidic lower than pH 4.5. Anions in the soil solution collected in the inter-row were mainly composed of NO3- and SO42- and the concentration of anions exceeded that of cations. The soil acidity was kept at pH 3 when alminium inos were available to compensate for the lack of cations.