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Introduction A significant portion of the surface irrigated cropland in the western United States is located in alluvial valleys. For example, in Wyoming an estimated 350,000 ha of the total of 730,000 ha of surface irrigated land is in alluvial valleys, and there are 21,000,000 ha of surface irrigated lands in the 17 western states (Anon. 1982). Soils in these valleys are typically sandy, and have very high water infiltration rates. The problem of high infiltration rates is particularly severe when minimum tillage practices are used in these soils.
Furrows are normally formed using a furrow opener. This device leaves the furrow surface relatively loose and rough. These factors contribute to high infiltration and to erosion and transport of sediments both within the field and with tail water.
A compaction roller will firm and smooth the furrow wall and bottom. Compaction reduces the infiltration rate, and water advances more rapidly across the field because of the smooth furrow surface. Water intake thus is more nearly uniform along the entire length of the furrow. Less total water is required and water is applied more uniformly. With appropriate compaction of irrigation furrows, crop production should be enhanced with less water and with reduced water degradation.
Although not directly addressed in current research, a significant possibility exists for savings of plant nutrients, particularly nitrogen. Assuming that 100mm of excess water becomes deep seepage on the 350,000 ha of surface irrigated area in the alluvial valleys of Wyoming and using values reported by Duke (1978), between 6,700 and 21,000 metric tons of nitrogen are leached to ground waters from alluvial valleys each year in the State of Wyoming. It should be noted that 100mm of deep percolation is a very conservative estimate. Additional benefits of furrow compaction include improved irrigation tail water quality because of reduced erosion and the corresponding reduction in sedinents transported to tail water collection facilities or streams.
Compaction of furrow walls provides several direct benefits to irrigation. First, compaction decreases the rate of infiltration of water from the furrow to the surrounding soil. Khalid and Smith (1978) reported approximately 40 percent decrease in the rate of infiltration from compacted furrows in sandy soil.
Soothing furrow walls significantly decreases the resistance to flow of water in furrows. Borrelli, et al. (1982) reported that water advanced approximately 40 percent faster in compacted furrows. The combined effect of reducing the infiltration rate and increasing the rate of water flow in the furrow is to provide a nearly equal opportunity time along the length of the furrow. This means that the uniformity of irrigation and the irrigation efficiency would be increased. Based on results reported by Borrelli (1982), the efficiency of surface irrigation with compacted furrows may be nearly equal to the efficiency of sprinkler irrigation.
The flowrates for all tests were in excess of 100 l/min while for a 0.5% slope, although the maximum nonerosive stream size was 76 l/min (Marr, 1967). By visual inspection, the higher compaction rate rows appeared to have less sediment loss than the noncompacted furrows.
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