基于茎直径微变化的棉花适宜灌溉指标初步研究

在2004和2005年棉花生长季节,采用筒栽和大田小区试验相结合,对不同水分状况下茎直径微变化动态中日最大收缩量(MDS)、日增长量(DI)和当日复原所需时间(RT)等3个关键性指标进行了研究。结果表明,3个指标对植株体内水分状况变化的反应均非常敏感,随着日出前叶水势的降低,MDS明显增大;DI逐渐减小,在水势较高时变化幅度较小;RT则大幅度延长。当叶水势降低到-0.1 MPa时,DI变为负值,RT维持在24 h。3个指标的株间变异性测定结果表明,MDS和DI均存在较大的株间变异系数,RT的变异系数最小。对RT与土壤相对含水率进行相关分析发现,两者之间呈幂函数关系,相关程度达极显著水平。根据RT与叶水势和土壤相对含水率的关系,确定了RT对应于棉花适宜水分、轻度水分胁迫和重度水分胁迫的变化范围,而且,在对应的土壤含水率范围内,RT维持在一个相对稳定的区间,说明RT可作为指导棉花灌溉的适宜指标。MDS和DI由于影响因素较多,难以确定对应于水分胁迫的临界值,不适于单独作为灌溉指标。

Rational indicators for irrigation scheduling of cotton based on microchanges of stem diameter

Both pot experiment and field experiment were conducted by continuous measurements of stem diameter variations, predawn leaf water potential and soil relative water content for growing cotton(Gossypium hirustum L. "Meimian 99B") in 2004 and 2005. The suitability of using parameters derived from stem diameter measurements, including maximum daily stem shrinkage(MDS), daily increase(DI), and recovering time(RT) as indicators for irrigation scheduling of cotton was evaluated. The results show that the above three parameters are highly sensitive to the changes of plant water status. As predawn leaf water potential gradually decreased, MDS increased markedly, DI decreased slowly and slightly-varying under relatively high predawn leaf water potential, and RT increased sharply, then remained 24 h when the predawn leaf water potential was below a critical level of -0.1 MPa. Nevertheless, there was relatively high plant-to-plant variability in the MDS and DI measurements. Compared with MDS and DI, RT had the lowest variability(CV of 5.02% and 8.5% under high and low water content respectively). For rapidly growing cotton, there was a strong power relationship between RT and soil relative water content (r²=0.7101). Based on the high correlation between RT and predawn leaf water potential and soil relative water content, the RT range corresponding to mild water stress and severe water stress was determined, and RT was relatively constant in corresponding range of soil water content. It is suggested that RT is a comparatively ideal parameter with its high sensitivity to water deficit and low variability when utilizing the stem diameter-derived indicators for irrigation scheduling in growing cotton, but it is difficult to use MDS or DI as a single parameter for irrigation scheduling as a result of its high variability and difficulty of determining a critical value corresponding to water stress.