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Title: Effects on wetting by spray on concentrated flow erosion and intake rate

Author
item JIAN, YU - INNER MONGOLIA, PR CHINA
item LEI, TING - BEIJING, PR CHINA
item SHAINBERG, I - AGRIC RES ORG, ISRAEL
item Iliasson, Amrax
item LEVY, GUY - AGRIC RES ORG, ISRAEL

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2006
Publication Date: 12/1/2006
Citation: Jian, Y., Lei, T., Shainberg, I., Mamedov, A.I., Levy, G.J. 2007. Effects on wetting by spray on concentrated flow erosion and intake rate. Soil Science. 171:929-936.

Interpretive Summary: Rapid wetting of dry soil by irrigation or rain water may cause breakdown of soil aggregates. If soil is wet before furrow irrigation, this condition may reduce aggregate slaking and may decrease concentrated flow erosion. Soil could be wetted by spray (like rain) or by flow (like furrow irrigation) with different intensity. We studied the effects of spray wetting intensity and furrow flow type (interrupted vs. continuous flow) on soil cumulative intake and cumulative soil loss of silt loam and clay soils. For the silt loam soil, spray wetting generally had no effect on cumulative intake and concentrated flow erosion. In this soil, the interrupted or continuous flow yielded comparable cumulative intake. In the clay, there was a critical spray intensity for aggregate disintegration. Below the critical intensity, spray wetting did not cause aggregate slaking and high concentrated flow erosion. When the spray intensity was higher than critical, spray wetting did not diminish concentrated flow erosion. Thus, in the clay soil, interrupted flow increased cumulative intake in comparison to continuous flow. The opposite response of the silt loam and clay soils to interrupted flow can be explained by differences in aggregate stability, which affects consolidation. Under stable soil aggregates, interrupted flow increased cumulative intake in comparison to continuous flow due to the elevated hydraulic gradient in the interrupted flow. But when surface aggregates were disintegrated, the complete consolidation of the soil surface by interrupted flow balances the favorable impact of the increased hydraulic gradient. Thus, cumulative intake under interrupted and continuous flow remained similar. The study describes soil stability conditions under which spray wetting before furrow irrigation could affect furrow erosion. In soils with an inherent aggregate and structural stability (clay soil), spray wetting may diminish concentrated flow erosion. In soils with a less stable structure (silt loam), spray wetting before concentrated flow does not affect concentrated flow erosion. The results can help in the adjustment of existing models and development of new models for the estimation of soil erosion with changes in irrigation practices and soil conditions.

Technical Abstract: When water flows in dry rills (or furrows), fast wetting and aggregate slaking occur. Conversely, when rain wets the surface of the soil before applying concentrated flow, slow wetting precedes the concentrated flow, and less aggregate disintegration occurs. It is hypothesized that slow wetting by tap water results in less concentrated flow erosion and less effect of interrupted flow on erosion and intake rate (IR). The objectives of this study were to (i) investigate the effects of wetting rate (WR) by spray and type of flow (continuous and interrupted flow) on IR and soil loss in concentrated flow, and (ii) compare the impact of wetting by spray with that of wetting the soil by concentrated flow on IR and soil loss in subsequent concentrated flow. Two soils, silt loam and clay, were packed in 0.5-m-long, 0.047-m-wide, and 0.12-m-deep flumes, and exposed to 3 and 4 WR by tap water spray (electrical conductivity of 0.95 dS m- 1 and mist size drops ranging in intensity between 2.5 and 300 mm h- 1 ) before the application of concentrated flow. Increasing spray WR decreased IR in the clay and had no effect in the silt loam. Soil erosion in continuous flow increased steeply with the increase in WR in both soils. Interrupted flow in the clay tended to yield higher cumulative infiltration compared with continuous flow. Conversely, in the silt loam, interrupted flow had no effect on cumulative intake. Interrupted flow was not effective in reducing erosion in both soils wet by spray. Comparing spray wetting with concentrated flow wetting, wetting of the dry soil with concentrated flow resulted in much higher soil loss. In addition, the effect of interrupted flow on soil loss was more pronounced in the concentrated flow wetting. The relation between WR, flow type, and soil properties with respect to their effects on erosion and IR was explained by the effect of clay content on aggregate stability and the effect of WR on aggregate disintegration.