Crop Residue Effects on Evaporation from Soils
Wheat residue saved nearly four inches of water compared to bare soil under sprinkler irrigation
Center pivot irrigation systems typically wet the soil surface 15-20 times during the irrigation season. Each wetting cycle produces evaporation directly back into the atmosphere that is controlled by the amount of energy reaching the soil surface. Even with developed crop canopies, energy limited evaporation can be a substantial portion of evapotranspiration (ET). Klocke et al. (1985) measured E and T independently in fully irrigated corn grown in sandy soils and found that E was 30 percent of ET during the irrigation season.
Crop residues remaining on the surface have a role in reducing evaporation from soils. Todd et al. (1991) demonstrated that the equivalent of 6000 lb/ac of wheat stubble laying flat could reduce bare soil evaporation in half under a fully irrigated corn crop. This crop received only nine irrigation events during the growing season. Klocke (2003) reviewed this study and projected the full season evaporation (120 days) in Table 1:
The experiment was subject to 23 and 29 rainfall events during the two growing seasons, respectively. During 1986 only 6 of the events were between 0.5 and 0.75 inch and the rest were less in accumulation. These small events led to the preponderance of soil limited evaporation in the dryland treatment. The canopy had similar effect as the straw reducing evaporation in the cropped situation. The straw was not very effective in the fallow situation either because of the transient nature of energy limited evaporation effects when rainfall amounts are small and scattered. However, the benefits of straw cover for runoff control and capture of soil moisture, snow capture of soil moisture, and evaporation suppression when the large events occur will become evident.
The reduction in evaporation in the fully irrigated management of 6.8 inches due to the crop canopy and an additional 3.8 inches was due to the straw mulch. This savings of nearly 4 inches of water in evaporation due to the crop residue is only part of the story. This savings was measured during 120 days of the growing season. The other benefits for crop residue are present then and during the rest of the year including runoff control and soil moisture capture and snow capture. These other benefits could easily add 2 inches or more of soil moisture to irrigation programs, as has been documented by dryland systems with residue management.
Other types of residues need to be considered to suppress evaporation including corn stalks and standing wheat stubble. Whether or not they will be as good as flat wheat stubble for suppressing evaporation will be the subject of future research.
| Table 1. Growing season evaporation from soil surface. | |
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References
Klocke, N.L. 2003. Water savings from crop residue in irrigated corn.
In Proceedings. Central Plains Irrigation Conference Proceedings. Colby,
KS. Feb. 4-5, 2003. pp. 134-142.
Klocke, N.L., D.F. Heermann, and H.R. Duke. 1985. Measurement of evaporation
and transpiration with lysimeters. Trans. of the ASAE. 28:1:183-189 &
192.
Todd, R.W., N.L. Klocke, G.W. Hergert and A.M. Parkhurst. 1991. Evaporation
from soil influenced by crop shading, crop residue and wetting regime.
Trans. of the ASAE. 34:2:461-466.
