| Water production function and efficiency of cotton under mulched drip irrigation |
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| DOI：10.7606/j.issn.1000-7601.2016.04.04 |
| Key Words: drip irrigation under mulching cotton water production function water use efficiency irrigation efficiency |
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| Abstract: |
| This paper discusses the relationship between the amount of irrigation and the yield of cotton. Statistical analysis of experimental data on cotton under mulched drip irrigation during 2007—2012 indicates that the relationship between yield of cotton and irrigation presents a quadratic parabola in Tarim irrigated area. The irrigation norms for the highest yield, for the highest water use efficiency, and for the highest benefits, and the critical period of water requirement in cotton were analyzed by mathematical method. Best fit model of cotton water production function was adopted by least squares theory on the basis of field experimental data of cotton. Water production function is a quadratic function and its math expression is Y=0.0026 I2+18.015I-24845 (R2=0.9592，n=6). Water productivity is divided into three different development stages according to the changing rule of water use efficiency and the relationship between yield and irrigation. Irrigation amounts less than 3 091 m3·hm-2 are identified as the first stage when yield rises with the increase of irrigation amounts, and productivity rises gradually at this stage. Irrigation amounts at the second stage rises from 3 091 m3·hm-2 to 3 464 m3·hm-2 and the yield still rises with the increase of irrigation amounts, but the range is reduced. Irrigation amounts at the third stage exceed 3 464 m3·hm-2 and the yield is reduced with the increase of irrigation amounts. Negative rise occurs and productivity is declined. The analysis of cotton irrigation production function and the water requirement law indicates that the critical periods of water application for cotton are at the flowering stage and budding stage. The rational irrigation norm, norm for the highest yield, and norm for the highest water use efficiency for cotton are 3 091 to 3 464 m3·hm-2, 3 464 m3·hm-2, and 3 091 m3·hm-2, respectively. The best benefits point of irrigation efficiency of cotton is not the highest point of utilization ratio of water or the highest point of yield, but within the 3 091～3 464 m3·hm-2 interval. When marginal benefit equals marginal cost, net income of irrigation on cotton is the biggest. The maximal net income and net income of unit of irrigation amounts are 24 333.1 yuan·hm-2 and 7.23 yuan·hm-2, respectively, and irrigation amounts is 3 459 m3·hm-2 at this time. Compared with the irrigation norm for the highest yield, it saves 5 m3·hm-2 of water, meanwhile water use efficiency and net income of unit of irrigation amounts are increased by 0.003 kg·m-3, 0.21 yuan·hm-2, respectively, whereas the yield is almost the same. |
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