咸水灌溉棉田保证棉花优质高产的土壤盐度指标控制

Index controlling soil salinity for cotton field with salt irrigation subject to high quality and yield

为了探索由咸水灌溉引发的次生盐渍化棉田适宜的土壤盐度控制指标,试验于2012年在5个不同次生盐渍化水平的小区开展,0-60 cm深土层的初始土壤电导率（土水质量比为1∶5）分别为0.29、0.32、0.55、0.79、0.99 d S/m,分别以处理1-5表示。研究分析了盐分对棉花＂三桃＂比例、产量和纤维品质的影响,并建立了棉花价格模型,最后通过拟合分段式作物耐盐函数得出土壤盐度控制指标。结果显示,在平水年时降雨基本满足棉花需水要求,而且土壤中很大一部分盐分被降雨淋洗出0-60 cm深土层,并被控制在100 cm以下的土层中,与试验初始相比,处理1-5的最大脱盐率分别为9.6%、19.8%、36.4%、42.4%和45.7%,最终脱盐率分别为9.4%、1.8%、21.0%、24.5%和31.7%。当0-60 cm深土层初始土壤电导率低于0.79 d S/m时,没有显著降低成铃数和籽棉产量,仅会改变＂三桃＂比例,随土壤盐度进一步增高,成铃数和籽棉产量显著降低。棉花衣分率和纤维品质指标受到采摘时间和土壤盐度的共同影响,仅马克隆值在3次调查中都随着土壤盐度增加呈增大的趋势。由棉花净收益决定的土壤盐度指标低于由籽棉产量决定的土壤盐度指标,证明考虑纤维品质指标的必要性。在与处理1的净收益相比不降低的情况下,棉花播种初始和生育期平均土壤电导率应该分别控制在0.71和0.67 d S/m以下。该研究为改善次生盐渍化棉田土壤盐度控制指标的确定方法提供了理论参考。

Drought and water shortage have stimulated saline and slight saline water use for farmland irrigation in Hebei Plain. The mismanagement of irrigation with saline water has led to the expansion of secondary salinization farmland recent years. Therefore, it is urgent to explore suitable control index of soil salinity in order to avoid the reduction of crop production. This study was conducted in cotton field with five secondary salinization levels, which were caused by seven years continues irrigation with different salinity of saline water. The initial soil electrical conductivity（mass ratio of soil to water was 1：5） of the 0-60 cm soil layer depth was 0.29, 0.32, 0.55, 0.79, 0.99 d S/m, and denoted by treatment 1 to treatment 5 respectively. In this study, the response of cotton boll forming, yield and fibre quality to five soil salinity levels were analyzed, and price model for cotton was set up, at last, soil salinity control index were obtained by fitting piecewise function for crop salt-tolerance. Results revealed seasonal rainfall（450 mm） basically met the requirements of cotton water consumption under median water year（about 500 mm precipitation）. Moreover, large part of the salt in soil was leached out of the 0-60 cm depth soil layer, and was controlled bellow 100 cm. When compared with the initial soil salinity for 0-60 cm depth soil layer, for treatment 1 to treatment 5, ratio of the maximum desalinization was 9.6%, 19.8%, 36.4%, 42.4%, and 45.7% respectively, and the ratio of the final desalinization was 9.4%, 1.8%, 21.0%, 24.5%, and 31.7% respectively. No significant decline in number of cotton bolls and seed cotton yield was found when the initial soil salinity for 0-60 cm depth soil layer was lower than 0.79 d S/m, while the ratio of cotton boll forming changed. With the further increment of soil salinity, the number of cotton bolls and seed cotton yield of treatment 5 were significantly lower than that of treatment 1 by 28.9% and 6.5% respectively. Lint percentage and fibre quality were affected by picking time and soil salinity. With the increment of soil salinity, increasing trend occurred in micronaire for all three batches of lint and in fibre strength for the first two batches, but the upper half mean fibre length significantly decreased for the second batch. Price model for cotton was set up, in which, cotton price of each batch was decided according to price list for different lint fiber quality published by China Cotton Association. It was observed that the control index of soil salinity decided by net earnings were lower than that decided by seed cotton yield, which proved the necessity of the consideration of fiber quality index. The initial soil salinity and mean soil salinity during the cotton season for 0-60 cm depth soil layer should be lower than 0.71 d S/m and 0.67 d S/m respectively, when the net earnings was consistent with the treatment 1. The study provides an important theoretical reference for improving the method of deciding control index of soil salinity for cotton field subject to secondary salinization.