Water infiltration rate in cracked paddy soil

The surfaces of paddy fields may crack into fissures as a result of drainage and exposure to sunlight after rice harvesting. Field observations indicate that a cracked paddy field has a significantly increased rate of infiltration. Yet, the infiltration rate drops considerably after 2 days of precipitation. A laboratory soil column experiment was performed to identify the parameters that control the infiltration of water in a cracked paddy field. Various variables, including soil texture, flooded water depth, fracture apertures, cultivation practices and water suspended particles, were investigated to quantify their influence on the infiltration curves and the closure mechanism of a fractured plough pan. The experimental results reveal that increased fracture aperture and flooded water depth only temporarily increase the rate of infiltration. Soil swelling most strongly affects the rate of infiltration. When cracked, swelling soil mixtures are flooded with water that is rich in clay particles. The swelling gradually closes the fissures, healing the fractured plough pan. Ploughing and compaction of the surface soil can also enhance the recoverability of the plough pan and reduce the infiltration rate. The structures of soils with low bulk densities are easily changed following infiltration by water. Infiltration also disperses clay particles and redeposits them on the surface of fissures via surface filtration, significantly reducing the infiltration rate. Thus, the removal of the plough pan from the paddy may effectively increase infiltration. This study proposes an efficient water-using paddy layout that effectively uses irrigation water in agricultural water management. Converting half of the paddy acreage into a. water pond and an upland crop area saves a considerable amount of irrigation water, which can be used to supplement ground water. (C) 2003 Elsevier Science B.V. All rights reserved.