ABSTRACT
In irrigated areas of the West, agriculture uses about 80 percent of all ground withdrawals with irrigated cotton accounting for 15 percent of it. In the deep groundwater lift areas, water represents 20 to 40 percent of total variable costs. Also, those who formulate water policy may restrict water allotted to agriculture. Irrigation, though costly, has been one of the premier crop risk reducers in agriculture. Limited water and increasing costs place emphasis on reducing unit production costs. And we all know the best way to do that is to go for high yields. Improved irrigation systems should assure a more uniform crop and income from year to year--something that keeps lenders much easier to live with. Timing of the first irrigation is critical. Rule of thumb holds that young plant growth is stimulated by an irrigation when about one-half of the available soil moisture remains in the root zone. Heavy shedding early can usually be attributed to specific causes. Many can be corrected. Natural causes--physiological--account for only 10 percent in early season. Irrigation regimes with water stress usually have higher water use efficiency, but the highest yield and highest net return comes from cotton that receives adequate water throughout the season. In the event of a water shortage, normal irrigation practices on reduced acreage will give higher net return than restricted irrigation on all acreage. In scheduling irrigations, most growers rely on intelligent observation of the behavior of the plant, coupled with a knowledge of the soil moisture conditions. Drip irrigation may reduce the use of valuable water resources by about 40 percent and to potentially increase line yields by 25 to 50 percent when compared to average values. However, drip irrigation requires more careful management than conventionally irrigated cotton.
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