Effects of the Underdrain and Irrigation on the Growth of Young Tea Plant

Abstract

Generally, the irrigation are effective for the protection from the drought injury, but the excessmoisture injury caused by the irrigation sometimes occurres tea planted on poorly permeable soil and poorly drained in subsoil. Therefore, the effects of the underdrain and irrigation on the growth of tea plant cultivated on the clayey and poorly permeable soil were investigated.
Three-year-old tea plants were used for the experiments. The yield of 1st crop and the spread of plant were increased by the underdrainage treatment. It was considered that the increase of the yield of 1st crop by the underdrain was mainly due to the increase of plucking area because the significant positive correlation was recognized between the yield of 1st crop and the spread of plant. Moreover, it was considered that the increase of the yield of 1st crop was mainly affected by the increase of the gaseous phase ratio of soil down to sublayer by the underdrainage treatment.
The growth of summer shoot, namley the weight of pruned branches on July 9was increased by both the underdrain and irrigation, however irrigation was more effective. The weight of summer pruned branches was mainly affected by the amount of extracted soil moisture, and the amount of extracted soil moisture was increased by the irrigation and remarkably increase was shown in the plot of underdrain at drought period. The soil moisture was gradually extracted from all soil layer in the plot of underdrain, but the soil moisture was extracted from surface layer only in the non-underdrain plot.
The growth of autumn shoot, namely the weight of pruned branches on Oct. 28 was increased by the underdrain, and it was decreased by the irrigation without the underdrain. The weight of shoots in a unit area and length of shoot were increased by the underdrain, and they were highly increased by the irrigation in addition to the underdrain. The spread of plant was increased by the underdrain, and decreased by the irrigation with or without the underdrain, and the spread of plant mainly affected the weight of pruned branches. It was considered that the increase of gaseous phase ratio of soil down to the sublayer by the underdrain affected the increase of the spread of plant, and also affected the increase of the weight of autumn pruned branches.
From the results above mentioned, remarkable effect such as the continuous increase of the gaseous phase ratio in the soil and hastening the growth of young tea plant were shown in underdrainage treatment. Otherwise, the effect of irrigation was recognized at only drought period. Accordingly, it is considered that the supply of air into the soil by the underdrain was more important than the supply of water by the irrigation on the growth of tea planted on the poorly permeable soil.