Behavior of inorganic nitrogen in tea [Camellia sinensis] field soils heavily applied with nitrogen and changes in amino acid content of the first crop accompanying the reduction of nitrogen

We investigated the behavior of nitrogen heavily applied to inter-row spaces of the fields and the deterioration in amino acid contents caused by the reduction in nitrogen. The concentrations of inorganic nitrogen in soil solution collected from inter-row soil layers at different depths showed the maximum level in August. A high correlation was found between the amount of nitrogen applied and the concentration of inorganic nitrogen in soil solution. The average concentration of inorganic nitrogen in soil solution collected from inter-row soil layers and under canopy edge was significantly high at 495 ppm, while that in the soil solution collected under the canopy ranged from30 to 100 ppm. A reduction in the amount of nitrogen supplied resulted in a decrease in the amino acid content in green tea leaves in the first year, regardless of the amount of nitrogen applied. However, the total content of amino acids in lower application plots recovered to almost the same level as that in the heavy application plot in the second year. This deterioration in the amino acid content in the first year after reduction in nitrogen application seems to mainly attributable to a growth disorder of roots caused by the preceding heavy application of nitrogen