Evaporation from soil in relation to residue rate, mixing depth, soil texture and evaporativity

The role of crop residues as a surface mulch on evaporation has been widely studied. But information on evaporation and its reduction by crop residues mixed in surface soil to different depths particularly in relation to soil texture and evaporativity (E_o) is lacking. We studied 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 mm day⁻¹ in silty clay loam and sandy loam soil columns of 0.95 m length and 0.1 m diameter. Cumulative evaporation was predicted from water 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 residue was mixed with soil at peak reduction, and as a result the benefit was prolonged. The maximum reduction achieved was more and sustained for a longer period in finer textured soil, and a higher rate 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.