5. Conclusions
Soil evaporation depended on meteorological and experimental conditions, stage of evaporation (energy-limited or falling-rate stages) and type of mulching materials. Soil evaporation increased linearly with increases in soil water content in the falling-rate stage, but these increases were much lower in the mulched than in the bare soil because of the lower energy available for evaporation at the mulched soil surface.
All mulching materials decreased soil evaporation in the energy-limited stage in relation to the bare soil, but the decreases and their significance varied among the two experiments. In experiment 1 (soil trays), the average daily soil evaporation rates (ER) were different (p < 0.05) among all mulching treatments, with highest ER decreases in plastic and pine bark, and lowest ER decreases in geotextile and vine residues with a 5 cm thickness. In experiment 2 (microlysimeters) where, in contrast with experiment 1, the mulching materials were not in contact with the wetted soil, the geotextile was more beneficial than the pine bark for soil evaporation control.
During the falling-rate stage where evaporation is controlled by soil water content, the evaporation rates were low and similar among treatments, suggesting that soil mulching will be inefficient for soil evaporation control in low-frequency irrigation systems where the soil remains dry most of the time. During the energy-limited stage, the plastic and pine bark materials in contact with the wetted soil were most effective for evaporation control. These materials will be therefore recommended in high-frequency irrigation systems because of the high and almost continuous wetting of the soil surface in these systems. Only in cases were the mulching materials would not be in contact with the wetted soil, the geotextile will be recommended over the pine bark for soil evaporation control.