Root zone moisture characteristic of soil under different grape varieties

Abstract

A Study on characteristic of moisture content within root zone of different grape varieties was conducted in Kanchanaburi Research Station, Wang Dong subdistrict, Muang district Kanchanaburi province, aiming at comparing the change of soil moisture at different depths in six grape plantations and bare land, using TDR (Time Domain Reflectrometry) to monitor soil moisture, and also examining soil property related to soil moisture distribution of the soil. A representative soil was classified as Typic Haplustalf, having developed from local alluvium over residuum of limestone. Available water capcity of this soil varied between 6.58-9.23% by volume. Result revealed that moisture content at depths between 0-30 cm was mostly lower than the critical value (21.724.9% by volume) measured at -50 kPa matric potential. due to the loss by evaporation. Soil moisture distribution with depth in table grape was better than in vineyard grape, especially at depths between 60 and 100 cm, which the former had more moisture stored in soil than did the latter. This may be because all table grapes were grown on the lower position of the landscape than that of vineyard grapes, and/or vineyard grape tended to have deeper rooting zone than that of table grape. Plastic roof resulted in moisture content during raining period being lower than those without roof due to not receiving additional rain water while surface moisture mainly evaporated. Weed control that left the soil surface underneath grape canopy bared, accelerated the evaporation of soil surface moisture more rapidly. Irrigation with 20 litres per plant, every three day did not help moisture content at depths between 0 and 30 cm of most plots to increase above critical moisture level for grape. Therefore, irrigated water should be applied more frequently, particularly during fruiting stage or 11-12 weeks after the last rain due to moisture deficit at depths from 0-60 cm as indicated by data obtained from this study. Soil surface cover using crop residues or mulching would help conserve moisture at surface layers and incorporation of organic matter into the top soil would help improve water holding capacity of this soil.