喷灌条件下土壤水分空间分布特性研究

Spatial Variability of Soil Moisture Under Sprinkler Irrigation

分别在火山灰土和砂壤土两种土壤上进行了不同喷灌均匀系数和灌水量的土壤水分空间分布试验。对土壤干容重空间分布规律的研究表明，干容重在空间的随机分布可用正态分布来表示。为了确定喷灌洒水量和土壤含水率的空间结构，分别计算了它们的半方差和自相关函数。结果指出，喷灌洒水量的相关距离为４～６ｍ，该距离随风速呈增大趋势；灌水停止２４ｈ后的土壤含水率的相关距离为５～６ｍ，喷灌均匀系数对该距离无明显影响。田间试验还表明，喷灌洒水在土壤中的分布要比其在地表的分布均匀得多，土壤水分空间分布的均匀性主要取决于土壤初始含水率的均匀程度和灌水量。

Crop yield response to sprinkler irrigation depends mainly on the spatial distributions of applied water within the root zone, however, we have quite limited knowledge about it. The redistributions of water in the soil were therefore observed under the conditions of sprinkler uniformity ( CU )ranging from 53% to 98% and application amount from 5 to 58 mm, on two different soil types——a volcanic ash soil and a sandy loam soil. The distribution of bulk density was examined and showed that it can be represented by a normal distribution function for both soil types. The autocorrelation functions and semivariograms were calculated for water application and soil water content 24 h after application ceased to determine their spatial dependency. Sprinkler water application demonstrated a correlative length of 4 to 6 m, which increased with wind velocity during the experiments, but water applied by a rainfall event was spatially independent. Soil water contents for 24 hrs after water application ceased exhibited a correlative length of 5 to 6m and appears to be independent of application uniformity. The field experiments also showed that the water was more uniformly distributed in the soil than sprinkler water applied on the ground surface, and the uniformity of water in the soil was closely related to the uniformity of initial soil water content and the total water applied.