Coupled heat and moisture transfer and evaporation in mulched soils.

Improving water efficiency in arid and semi-arid regions is an ongoing goal in agricultural production. Straw mulching is one cultural practice which can be used to this point. Mulch layers associated with the atmospheric condition can create a variety of water and heat flux conditions at the soil surface. This study was conducted to (a) analyses the effect of a straw mulch layer on coupled heat and moisture transfer in shallow depths compared to bare soil, and (b) to develop and evaluate a method to estimate soil evaporation. Experiments were conducted in a field with grass clipping mulch and sandy soil that was moistened with natural shower and included a weighing lysimeter to measure actual evaporation. Average albedo over the mulching plot was defined as 0.49 by using lysimeter data during experiment. Near 93% and 97% of vapour flux in mulching plot and bare soil plot was under effect of temperature gradient, respectively. On average, the contribution of water vapour flux to the total moisture flux was 2% for mulching plot and 7% for bare soil plot. The heat transported by latent heat flux was 15% for mulching plot and up to 22% for bare soil plot. Observed differences between cumulative evaporation estimations and lysimeter data was about 8%. The simplicity of proposed method reduced required incoming solar radiation information, R s , to estimate evaporation. Mulch layer could reduce significantly evaporation amount 40%. [ABSTRACT FROM AUTHOR]