Management of cracked soils for water saving during land preparation for rice cultivation

High water loss during land preparation of soils for rice (Oryza sativa L.) production results from bypass ̄ow through cracks. It was hypothesized that the losses can be reduced by measures that minimize crack development during the soil drying period or impede the ̄ow of water through these cracks. The effect of straw mulching and shallow surface tillage on crack formation during the fallow period, and on water ̄ow components during land preparation was investigated in ®eld experiments on an Epiaqualf and a Pellustert in the Philippines. Cracks did not completely close upon rewetting, resulting in high loss (152± 235 mm of water) during land preparation of the control (i.e. no soil management treatment) plots. Straw mulching helped conserve moisture in the soil pro®le, and reduced the mean crack width by 32% of the control. Mulching did not signi®cantly reduce mean crack depth and the amount of water used in land preparation. Shallow tillage formed small soil aggregates which made the crack water ̄ow discontinuous and impeded groundwater recharge from the water ̄ow through cracks, reduced total water input for land preparation by 31±34%, equivalent to about 120 mm of water. The average surface irrigation water ̄ow advanced faster and less time was needed for land preparation in the shallow tillage plots compared to the control. Shallow tillage offers a practical means for improving water-use ef®ciency of irrigation systems. In rainfed areas, it may facilitate early crop establishment and, thus, reduce the risk of late-season drought. # 2000 Elsevier Science B.V. All rights reserved.