Soil moisture characteristics of red soil profile in drying course and soil layer drought index

A quantitative drought index is necessary for soil water management and crop yield evaluation. The drought experience of soil and crop could be described perfectly by combining drought intensity (I) with drought degree (D). Soil drought intensity is a function of water loss in soil profile, and its injury on crop is aggrandized and cumulated gradually, which turns into drought degree (D). Accordingly, soil layer drought index formulations, which were composed of drought intensity (I) and drought degree (D), were proposed. A six-treatment experiment was conducted in field in which soil drying lasted 12 days to 36 days from maize heading stage, the soil profile moisture characteristics and the soil layer drought index were analyzed. Results show that the soil moisture of red soil profile below 40 cm decreases slightly during the drying course, revealing the maize root took up soil available water from 0 to 40 cm layer for the most part. The soil water movement at 30～40 cm layer can indicate the drought degree of the maize plant. After soil drying lasted 25 days in the maize heading stage, the soil moisture below 40 cm decreases obviously, and the maize grain yield decreases significantly, when soil layer drought degree (D) at 0～60 layer reaches 0.55, equaling to that of at 30～40 cm layer. Thus the value of the drought degree could be used as an index for irrigation.