Crop Threshold Response To Progressive Soil Drought And The Quantitive Formulation For Red Soil Drought Degree

In the red soil region in the south of China, serious seasonal drought exists. It is important to quantify the soil drought degree and soil-crop drought threshold for drought evaluation and soil water management. There are a few quantitative ones among multitudinous drought indexes and the quantification index based on the soil moisture is less. In view of the question, experiments were conducted to investigate the effects of drought on crops in a greenhouse in the red soil region in the XianNing, Hubei province, during March to October, 2005. Six water treatments with progressive 12d~36d droughts were designed for the plotted-maize. In the same time, seven water treatments were maintained for the potted-peanut, by drying 4d~25d progressively. Soil water content and soil water potential of each soil layer were monitored with 10cm interval by the profile water content meter, which was made by Delta-T Corporation, and tensiometers. Regular measurements of leaf shape (including leaf area, height of plant, and stem diameter), stomatal conductance and plant output constitution, and so on, were measured in the drought duration of maize and peanut. After harvests the biomass and testing seed were surveyed. The main results were as follows.Threshold response to soil drought were observed in peanut morphologies and physiological indicators on a certain soil drought degree. After maize drought surpassed 25d, the output, the leaf area and the stomatal conductance dropped obviously; after peanut drought surpassed 12d, the biomass, the leaf area and the stomatal conductance lead dropped obviously. Sensitive degree of crops' various shapes and physiological indexes to soil drought was different. The leaf area, the stomatal conductance, the biomass, the output, maize's root system and peanut's main stem height were sensitive to the drought, which could be used as a crop water stress index; the maize's height was insensitive to the drought. The above results showed that the shape and the physiological indexes to quantify drought degree were unstable and the choice of index was difficult.In the drought duration, the soil moisture tendency and water balance were analyzed. It was found that moisture content change characteristics of a certain soil layer have a corresponding relation to the crops threshold response. In 12d-21d drought duration, the loss speed of the plot maize water content in the 0-40cm soil layer is biggest, and in 25th drought, the moving speed of the deep soil water content became big bviously. However the in-deep soil moisture content maintained a high level throughout drought duration. The 20-40cm soil layer's moisture content change characteristic was similar to the 0-100cm soil layer's. The soil water potential of peanut in 0-30cm soil layer was lowest in...