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 sediments transported to tail water collection facilities of 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.
As indicated above, Borrelli (1982) and Khalid and Smith (1978) used compaction to control furrow irrigation. However, neither of these investigations provided an overall analysis of the potential benefits of furrow compaction. Further, although both of these investigations produce considerable information required for the design of the compaction system, neither research effort evaluated the compaction system.
The current research was conducted during the 1985 growing season at the University of Wyoming, Powell Research and Extension Center. At Powell, the experiments were conducted on conventionally tilled dry beans with a furrow length of 320m. Water was delivered using 50.8mm siphon tubes. The soil at Powell was classified as a clay loam, but its irrigation characteristics resembled those of a coarse sand. The soil formed very coarse granular aggregates and thus, had high water intake rate and required an initial flow rate in excess of 90 l/mln to move water down the furrow at a reasonable rate. The maximum flow rate for non-erosive flow should have been less than 76 l/min (Marr, 1967).
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