Environmental Problems Caused by Heavy Application of Nitrogen Fertilisers in Japanese Tea Fields

Abstract

Nitrogen fertilisers are widely and heavily used in tea (Camellia sinensis L.) fields in Japan, which can result in environmental degradation. The current application level is often over 800 kg N ha−1 y−1. Field investigations and plot experiments were carried out in Shizuoka, a major tea growing region in Japan, to assess the environmental problems induced by heavy N fertilisation in tea cultivation. Results showed that long-term tea cultivation caused strong soil acidification. More than 77% of the tea fields investigated had soil pH values lower than 4.0, and more than 60% had pH values below 3.5, with a lowest value of 2.7. Root growth in the top 0–40 cm of inter-row soils was retarded when fertiliser N-input was over 800 kg ha−1 y−1. Noticeable water contamination in ponds, rivers and deep wells surrounding the tea fields was observed. The water samples investigated had annual average NO,-N concentrations of 10–60 mg L−1, and pH values ranging from 3.9 to 7.0 with an average value of 5.6. The water contamination has also caused fish deaths in some ponds. The N2O production potential (N20 loss without chemical fertiliser N-input) in the tea fields was as high as 32 kg N ha−1 y−1, and the annual N2O emissions from the tea fields were 32–97 kg N ha−1, increasing with the fertiliser N input rate. It was estimated that the amount of annual N20 losses from tea fields, which comprise 1.05% of the total area of arable land, was almost equal to that of the total amount lost from all other arable lands in Japan.