冬小麦根系生长与土壤水分利用方式相互关系分析

１９９５～１９９６年在中国科学院栾城农业生态系统联合站布置了冬小麦水分试验，在土壤连续干旱条件下考察了冬小麦返青至成熟阶段根系生长和土壤水分利用方式。给出并验证了可用于分析二者相互关系的定量模型。根据以下两点分析了作物利用土壤水分特征：①将土壤含水量开始降低时间视为吸水峰到达某一深度时间；②吸水峰下达到某一土层后，土壤含水量即随生育进程以指数形式逐渐降低。愈接近地表的土层，根系分布量愈大，根系日增长率在抽穗期最大，至扬花期根量及根深达最大值，根系吸水范围和深度基本取决于营养阶段根系生长发育状况。返青时，根系已下扎到１ｍ，根系生长峰与吸水峰基本同步下移，根系下扎到某一土层后继续生长发育，直至土壤有效含水量只剩４０％～２０％时为止。根系下扎虽深达１８０ｃｍ，而且下层根系吸水功能较强，有效水量较大，但终因根系分布量太少，致使作物利用水分的土层深度只达１２０ｃｍ，吸收的水量大多来自０～６０ｃｍ土层。在土壤连续干旱条件下，土壤水分不足亦是制约根系吸水功能的一个重要因素。在作物利用土壤水分初期，根系吸水速率最大，随着土壤含水量逐渐减少，根系吸水速率随之降低。土壤中有效含水量比例在０８以上，根系吸水速率大致以线性关系大

ANALYSIS OF ROOT SYSTEM GROWTH IN RELATION TO SOIL WATER EXTRACTION PATTERN BY WINTER WHEAT UNDER WATER LIMITING CONDITIONS

An experiment was conducted under continuous drying conditions in the field to examine root system growth in relation to water extraction pattern by winter wheat from 1995-1996 at Luancheng Experimental Station of Agricultural Ecosystems, Chinese Academy of Sciences which is located in the North China Plain. A model for analyzing the relationship between soil water extraction and root growth was put forward and verified. Extraction was analysed in terms of two components: (a) the time when the extraction front reaches a particular depth is defined as the moment when soil water content(θ) begins to decline exponentially with time, and (b) the decline of θ with time occurs at each depth after the extraction front arrives.Root length density declined gradually with depth, the period of fastest growth of root occurred after early head before anthesis and root length in each layer reached a maximum during flowering stage. The effect of soil water on root growth was little after anthesis, which implies that the depth and volume of soil water extraction by winter wheat mainly rely on the root length accumulation and downward penetraction during vegetative phase. The root front penetrated down to 100cm deep before jointing, thereafter the extraction and growth of root fronts descended together. Once the root front arrived at a given depth, root proliferation continued until about 40%-20% of extractable water in the layer remained. Although the maximal depth of root front penetration was up to 180cm, the ability of water uptake by root was strong and the amount of soil water available to winter wheat was much more in the lower layers, yet as the distribution amount of root system was too less that the extraction front could only arrive at 120cm, and most amount of water required by winter wheat come from 0-60cm layer.Under soil continuous drying condition, the deficiency of soil water was one of the important factors which restricted the ability of water extraction by root. The peak of extraction rate per unit root length (q) occurred near the beginning of extraction each layer. As soil dried, q declined substantially in approximate linear relationship with the fraction of extractable water (FEW) as FEW was more than 0.8.