科研之友
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摘要
A five-year field study (2007-2011) of irrigated alfalfa production with a limited water supply was conducted in southwest Kansas with two years of above-average precipitation, one year of average precipitation, and two years of below-average precipitation. The irrigation treatments were designed to reflect the declining ability of the aquifer to supply water for irrigation, the constraints of water rights, and irrigation management that either distributed water over the growing season or withheld water during the most stressful part of the growing season. Dry matter yields, averaged over irrigation treatments, declined from 1.68 kg m(-2) in the first year to 0.41 kg m(-2) in the final year because stored soil water contributed to crop evapotranspiration (ETC) in the first year; but precipitation could not replenish soil water in the following years, and stand densities declined over time. Annual yields, averaged over years, declined from 1.53 kg m(-2) with 610 mm of irrigation to 0.43 kg m(-2) for rainfed production. Annual yields were the same when irrigation was distributed over the growing season or withheld between the second and third cuttings. Crop productivity (water use efficiency) and plant stand decreased significantly as irrigation decreased and from the first through the final year of production. A linear regression of alfalfa dry matter yields with respect to evapotranspiration (ETC) produced an R-2 equal to 0.90. Yield response to irrigation was influenced by irrigation amount, precipitation, and the depletion of stored soil water from the beginning to ending years. Yields were highest in the first year, and the marginal yields decreased as irrigation decreased that year. Yield response to irrigation was nearly linear during the second through fourth years and linear during the fifth year with drought, indicating that alfalfa efficiently utilized irrigation and precipitation. Regression of yield-irrigation data from the middle three years of this study overlapped the results from a ten-year field study conducted at the same location from 1921 through 1930, demonstrating that similar alfalfa dry matter was produced with presumably similar atmospheric energy. Because the same irrigation treatment was in the same plot location for all years, available soil water (ASW) at the end of the previous growing season influenced the next year starting soil water content (a). All plant-available water was depleted during the first growing season to a depth of at least 2.4 m, and it was partially restored in only one other dormant season. In all years, 19, diminished to a value of 0.1 in the rainfed treatment, which was less than 0.15, the assumed wilting point for corn, grain sorghum, and sunflower in this soil. These results can be used to evaluate the economic viability of alfalfa production compared with other annual crops where limited water supplies lead to crop water stress.
- 出版日期2013-10
