基于产量响应诊断冬小麦水分亏缺适宜土层及其水分阈值

明确作物产量对水分亏缺的响应是实施非充分灌溉的科学基础。该文在华北气候下,通过设置不同灌水次数造成处理间的土壤供水差异,探讨了大田冬小麦籽粒产量与不同生育时期、不同土层深度的土壤水分之间的关系,系统分析了影响小麦产量的水分阈值,提出了适宜的土壤水分诊断深度。结果表明:不论从土壤水分动态、还是从全生育期平均水分来看,亏水处理与充分供水对照在浅层土壤的水分差异最大,且随土层深度增加而减小。0~0.4、0~0.8、0~1.2 m的水分差异分别在19.7%~36.5%、9.3%~21.7%和2.9%~9.7%之间。此外,土壤水分变异程度随土层深度增加而减小。不同生育期、不同深度的水分与小麦产量关系多为开口向下的抛物线函数,但函数关系的显著程度随生育期及土层深度而变化,其中0~0.4 m的水分与产量关系最为密切。影响小麦产量的水分阈值随生育进程呈下降趋势。自拔节孕穗至乳熟期,0~0.4、0~0.6、0~1.0、0~1.2及0~1.6 m的水分阈值由田间持水率的83.1%~95%下降到72.3%~90.0%。依据处理间土壤水分动态差异、全生育期平均水分差异、不同土层的水分变异程度、土壤水分与小麦产量关系显著性程度4方面的分析,该文提出0~0.4 m为适宜的水分亏缺诊断深度,相应在拔节孕穗、抽穗、开花、灌浆初期、灌浆中期、灌浆后期、乳熟期的水分阈值分别为95.0%、98.4%、79.9%、73.7%、88.6%、79.6%和75.7%。该结果对小麦亏缺灌溉管理具有实际指导意义。

Determination of soil depth and its water threshold for diagnosing water deficit of winter wheat based on grain yield

Abstract: Clarifying response of crop yield to water deficit is important for deficit irrigation. Field experiment of winter wheat with seven treatments, irrigated at different growth stages and supplied with varying irrigation schedules to maintain their variation in soil water, was conducted at a site in Hengshui, Hebei Province in North China Plain. The well-watered control was given four irrigations, and the most stressed treatment was rainfed. Each treatment had three replicates with plot size of 12 m × 8 m and was arranged in a completely randomized block design. Soil water was measured by TDR within 1.6 m soil depth at 0.2 m interval. Grain yield was measured on three 8-m2 area for each treatment. Meteorological data were collected through a weather station at the test site. By examining soil water dynamics, its average over growing season and its variability over soil profile, and by exploring the relations of grain yield of winter wheat with soil moisture of different depth at various growth stages, we determined suitable soil depth for detecting water deficit and its corresponding soil water threshold. We found that the largest difference in soil water between the deficit treated and well-watered control occurred at shallow soil layer, and the magnitude in difference decreased as soil depth increased, which was 19.7%-36.5%, 9.3%-21.7% and 2.9%-9.7% at the depth of 0-0.4, 0-0.8 and 0-1.2 m, respectively. Variability in soil water also reduced with increase of soil depth, shown by the average variation coefficient of all the treatments as 0.149, 0.129, 0.116, 0.108, 0.100 and 0.090 respectively for 0-0.4, 0-0.6, 0-0.8, 0-1.0, 0-1.2 and 0-1.6 m soil layer. Relationship between grain yield of winter wheat and soil water of various depths at different growth stages was described by downward-opening parabolic function, but the correlation significance changed with both growth stage and soil depth, being most significant during grain filling (coefficient of determination was 0.953-0.981, P< 0.01) and at the soil layer of 0-0.4 m. Soil water threshold that affected grain yield decreased with progression of growing season. From jointing-booting to milk maturing, they reduced from 95.0%, 91.1%, 83.1%, 86.9% and 94.1% to 75.7%, 73.7%, 72.3%, 74.3% and 90.0% of the field water capacity for the soil layer of 0-0.4, 0-0.6, 0-1.0, 0-1.2 and 0-1.6 m, respectively, indicating a diminished sensitivity of winter wheat growth to water supply. These results, the largest difference and variability in soil water at shallow layer, as well as the most close correlation between yield and shallow-layer soil water, all pointed to the fact that 0-0.4 m was the most suitable soil depth for detecting water deficit since large variability can give a stronger signal to be detected. The corresponding water threshold at jointing-booting, heading, flowering, beginning-, middle-, late-grain filling and milk maturing was respectively 95.0%, 98.4%, 79.9%, 73.7%, 88.6%, 79.6% and 75.7%. Since the detection depth of soil water deficit has never been studied as an important variable for deficit irrigation and that most previous studies concern threshold affecting plant physiological process, our results are of practical value for guiding deficit irrigation practice in wheat production and for ease monitoring of soil water in Northern China agricultural production areas.