Measurement of Vertical Water Percolation Through Different Soil Textures of Paddy Field During Rice Growth Season

The water percolation loss beyond root zone in the soil is one of the important parameters to determine water requirement of rice plant. If the amount of water percolation rate into the soil is estimated more carefully, determination of water requirement will be evaluated better and designing for system of irrigation, drainage and related establishments will be more easily done. The purpose of this research is determination the amount of irrigation water losses via vertical percolation in the paddy soils in rice growth duration. This study was carried out in a randomized complete block design (RCBD) with three replications in different areas of Guilan province in 1999. Seven areas which were different in the surface soil texture especially on their clay content or other particle size distribution were selected. For determining of water losses as vertical percolation was used quick method. The soils were sampled contemporary and the effects of some soil physical parameters on vertical percolation were studied too. The soil textures were consisted of: Sandy Loam, Loam, Clay Loam, Silty Loam, Clay and Silty Clay Loam. The results have shown that some physical parameters such as bulk density and particle size distribution especially clay content and sand fractions can be significantly effective on the amount of vertically percolated water. The values of adjusted determination coefficient of linear and nonlinear regressions (adj. R2) for above variables on vertical percolation for bulk density, clay, and sand percentage were 0.32, 0.91 and 0.79 respectively. The mean comparison of vertical percolation showed four different classes of vertical percolation at the 5% level by DMRT: Class I- Very high vertical percolation with 0.73 cm.day-1 or higher, in extremely light soil textures with clay contents less than 8%. Class II- High vertical percolation with 0.54 cm.day-1 in light soil textures with 8 -16% clay content. Class III- Medium vertical percolation with 0.32 cm.day-1 in medium soil textures with 16 - 44% clay content. Class IV- low vertical percolation with 0.15 cm.day-1 in heavy soil textures with more than 44% clay content.