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Irrigation scheduling programs were developed for cabbage and zucchini squash that produced high yield and water-use efficiency with a minimum number of irrigations. The irrigation programs are based on a soil water balance model developed by the USDA. The procedure involved selecting irrigation programs developed for similar crops and using them as standards for cabbage and zucchini for three growing seasons. The treatments involved irrigation levels higher and lower than the standard. After the third year, the best treatment for each year was selected. Coefficients for the standard model then were adjusted by trial and error to produce a program that called for the same number of irrigations and the same amount of water as the best-performing treatment when using the same weather data. These revised programs for cabbage and zucchini squash are available on computer disks and may be used on any IBM compatible PC provided wind, temperature, solar radiation, humidity, and precipitation data are available,
Water and nitrogen (N) are major inputs in the production of onions in the Arkansas Valley of Colorado. Because nitrates move with irrigation water, the effect of different rates of application of both N fertilizer and water on nitrate leaching were studied simultaneously. After a 2-year field study (1990-1991), it was concluded that >50 t·ha-1 of onions could be obtained without any N fertilizer when >42 ppm of nitrate nitrogen (NO3-N) were initially present in the top 33 cm of soil and up to 112 cm of irrigation water was applied. Total onion yield was not improved by applying more than the calculated irrigation requirement. The 2-m profile of soil under these experiments was found to contain >1400 kg·ha-1 of residual NO3-N prior to fertilizer treatments. When twice the estimated irrigation requirement was applied, >1000 kg·ha-1 of NO3-N was unaccounted for and presumed to have been mostly leached below the 2-m profile and partly denitrified. In both years, the onions were planted on land that had been fallowed the previous season, which does not help explain the presence of the high levels of nitrates found in the soil profile. It was concluded that sound water and N management practices in onion fields are crucial for preservation of water quality.
Abstract
Water use efficiencies of five irrigation methods on dry onions (Allium cepa L.) were compared in a two-year field study. The methods were: 1) graded furrows where water was measured into the upper end of the furrows and excess water was measured as it ran out the lower end; 2) level furrow where water was held in short, level furrows until infiltrated into the ground; 3) sprinkler; 4) trickle; and 5) trickle three times per week. Efficiency of water use (tonne per hectare per millimeter) was least with graded furrows and the same for the other four treatments in 1983, whereas there were no efficiency differences in 1984. Treatment differences in yield among onion grades occurred both years, but no differences in total yields among treatments for either year. The results do not justify the expense of conversion from existing furrow irrigation systems to pressurized systems for water savings on a uniform, heavy-textured soil where good-quality water is used.