SEASONAL VARIATIONS OF SOIL STRUCTURES AND HYDRAULIC CONDUCTIVITIES AND THEIR EFFECTS ON SOIL AND WATER CONSERVATION UNDER NO-TILLAGE AND REDUCED TILLAGE

Changes in soil physical properties in the surface layer( 0 ~ 20 cm) on a sloping farmland of Mollisols under no-tillage( NT),reduced tillage( RT) and conventional tillage( CT),separately,were monitored throughout the entire crop growing season for comparison to explore differences between soils under tillage patterns in seasonal variation of soil structure and hydraulic conductivity and relationships of the variations with soil-water loss. Results show that soil bulk density in NT varied slightly,remaining in the range of 1. 20 ~ 1. 30 g cm-3. NT was higher than CT in content of water stable soil aggregate 0. 25 mm size( WR 0. 25) and mean weight diameter( MWD),higher than RT and CT in initial and stable soil infiltration rate,4. 68% and 4. 44% higher than RT and NT in mean soil water content,and 86% and 100% lower than CT in runoff and soil loss,respectively. RT ranged between NT and CT in all the measured properties, throughout the season except in summer. In RT,deep tillage of the furrows in summer significantly lowered soil bulk density in the furrow,at least 0. 15 g cm-3lower than that in NT and CT,thus increasing the initial soil infiltration rate by 30% or more. RT was 20% and 40% lower than CT in soil and water loss,respectively. In CT,soil bulk density in ridge increased from 0. 91 g cm-3at the seeding stage to 1. 23 g cm-3at the harvesting stage,and that in furrow remained around 1. 30 g cm-3. CT was lower than the other two in WR 0. 25,MWD,soil infiltration rate and soil water content. It lost 10% of the rainfall it had during the entire the crop growing season and soil at 615 t km-2a-1. NT was rather stable in soil structure and the best in soil-water conservation among the three. Hence,it is a tillage practice significant in soilwater conserving effect. RT is also a practice that has some soil-water conserving effect. And both of the practices help improve soil physical properties.