红壤干旱过程中剖面水分特征与土层干旱指标

农田水分管理以及产量评估都需要对土壤作物受旱状况定量化和指标化。干旱强度和干旱程度结合才能完整地描述土壤作物干旱状况，土壤干旱强度I是土壤剖面失水速率的函数，干旱影响逐渐累积并增强就构成干旱程度D，据此提出了包含I和D二个指数的土层干旱指标表达模式。通过红壤小区种植玉米并在抽穗期开始设置连续干旱12～36 d等6个不同的处理，研究了红壤干旱过程中剖面水分特征和干旱指标。结果表明：供试红壤干旱过程中剖面40 cm以下含水率下降幅度很小，玉米主要利用了0～40 cm土层的水分，监测30～40 cm土层含水率的变化情况可以指示玉米受到干旱胁迫的程度。连续干旱25 d后40 cm以下土层含水率明显降低，玉米产量也显著下降，此时0～60 cm土层和30～40 cm土层的干旱程度D均为0.55，可用此指标作为灌溉的依据。

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.