Mulches evaporation losses

Cover the area with a thick straw mulch or pol3dhene sheet to prevent evaporation loss. 

Studies reported by Army et al. (1961) showed that the soil moisture content below 2 inches was not materially increased by surface residues. Evaporation losses during the summer months from both stubble-mulched and bare fallow soils constitute a high percentage of the total precipitation. A summary of many experiments conducted in the Great Plains showed losses during the fallow period of 76% of the precipitation. In other tests 83% of the rainfall was lost between the harvest of one crop and the seeding of the next (Mathews and Army, 1960). 

Mulching bare soil reduces water loss through evaporation and prevents germination of weed seeds. If a high- to medium-fertility soil improver is used, this also adds plant nutrients. Apply mulches to warm, moist soil in spring and summer. 

The main benefits from leaving crop residues on the surface are in the reduction of wind and water erosion their effects on evaporation are usually minor. When rain falls at comparatively short intervals, mulches of plant residues retard loss by evaporation for a time, but after the surface moisture has disappeared the stubble-mulched soils lose moisture about as fast as a bare soil. This is true chiefly because there is little movement of water by capillarity from the deeper horizons. The extra retention of surface moisture, even if temporary, is often beneficial to seed germination and also to increased infiltration and downward movement of rainfall. 

The above statements are illustrated in part by the studies of Greb (1966). He observed that wheat straw applied to the soil surface at rates of 1,120, 2,240 and 3,360 kg/ha, equivalent to 30, 60 and 90% coverage, reduced water losses from a wet soil surface by evaporation 16, 33 and 49%, respectively, during a 20-day period compared with no straw. An application of 6,720 kg/ha, or 180% soil coverage, was only slightly more effective than the 3,360 kg/ha application. As the soil water was evaporated the effectiveness of the mulches diminished. 

Li SX, Wang ZH, Li SQ, Gao YJ, Tian XH. Effect of plastic sheet mulch, wheat straw mulch, and maize growth on water loss by evaporation in dryland areas of China. Agric Water Manag 2013 116 (1) 39 9. 

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