Investigation of the Integral Energy Concept for Estimation of Available Soil Water in Paddy Soils of Guilan Province

To evaluate water, soil and plant relationships, soil water availability for plants is very important for irrigation management and scheduling. Integral energy shows the readily available water for plant in the range of soil available water. The purpose of this study was to investigate the concept of integral energy in 40 samples of paddy soils in Guilan province and to study the relationship between this index and various soil properties. The results showed that all soil samples had moderate to heavy texture. The mean Dexter S index in two soil textures including clay and clay loam was less than 0.35 (27% of the soil samples). The mean values of integral energy in the all studied soil samples, assuming the upper limit of soil water available at saturation, field capacity (at soil suctions of 100 and 330 cm) were 226.65, 270.21 and 336.91 J kg-1, respectively. The results showed that the soil texture classes with the highest value of integral energy were associated with the lowest values of S index. Moreover, the results confirm the better correlation between the calculated integral energy, assuming the upper limit at field capacity in soil suction of 330 cm, with the other soil properties. In addition, the integral energy values can be accurately estimated using soil saturation moisture and organic carbon to clay content ratio for silty clay loam (R2= 0.70) and clay loam (R2=0.95) textured soils, respectively.