EVAPORATION FROM SOIL IN RELATION TO RESIDUE RATE, MIXING DEPTH, SOILTEXTURE AND EVAPORATIVITY

The role of crop residues as a surface mulch on evaporation has been w idely studied. But information on evaporation and its reduction by cro p residues mixed in surface soil to different depths particularly in r elation to soil texture and evaporativity (E(o)) is lacking. We studie d the effect of four rates of paddy straw, viz. 0, 2, 4 and 8 Mg ha(-1 ) used as mulch and mixed in top soil layer to two depths (2 and 5 cm) under two evaporativities (E(o)'s) viz. 2.0 +/- 0.5 and 8.7 +/- 1.5 m m day(-1) in silty clay loam and sandy loam soil columns of 0.95 m len gth and 0.1 m diameter. Cumulative evaporation was predicted from wate r transmission properties of the soil and E(o) as influenced by these variables. The otherwise short-lived benefit of evaporation reduction with mulch per se, which peaked after a few days, plateaued when resid ue was mixed with soil at peak reduction, and as a result the benefit was prolonged. The maximum reduction achieved was more and sustained f or a longer period in finer textured soil, and a higher rare of mulch mixed to a greater depth. Mixing of residue in the surface soil layer not only reduced evaporation but also resulted in higher water content in the near surface soil after drying.