JWSS - Journal of Water and Soil Science

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In this study, the optimum irrigation depths for corn grain production under different conditions, i.e. maximum grain yield production and maximum benefit under limited land and water conditions, were determined under sprinkler irrigation in Bajgah (15 km. north of Shiraz).

 The results showed that, the optimum depth of irrigation for maximum grain yield production was 77.0 cm. Because of low price of irrigation water and sensitivity of corn crop to water deficit, the optimum depths of water were 76.8 and 73.4 cm under land and water limitations, respectively. Therefore, under limited water conditions, only 4.7 percent of the full irrigation water (maximum corn grain production) can be saved for maximum profits.

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In irrigation scheduling, one question is “how much is the optimal depth?”. In this study the optimal irrigation depth (by assuming the power distribution function and by taking into consideration the distribution function, which governs the data (normal distribution)) by considering the environmental effects was determined for three water management strategies (i. e. unlimited, limited nitrogen leaching and environmental protection) for wheat under center pivot irrigation system. The System layout in 32 hectare field was installed according to the ASAE standard. Four radial lines of catch cans were used at intervals of 6m (two radial lines of catch cans A and B, were installed on the maximum slope with 3˚ between every two rows and two radial lines of catch cans C and D, were installed on the minimum slope with 3˚ between every two rows). The field data were collected by the five different speeds of the center pivot system. The economical ratio (C) for three water management strategies were 31.19, 4.58 and 1.45, respectively. The optimum irrigation water was calculated for the three different management strategies. The results indicated that the lowest value of optimal irrigation depth was observed under the unlimited strategy, and the highest value of optimal irrigation depth was found for the environmental protection strategies (both with assuming power distribution and normal distiribution function).

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In order to investigate the effect of different levels of irrigation on qualitative and quantitative yield and determine the corn's optimum depth of Irrigation in sShahrekord, a randomized complete block design experiment was done with 7 treatments including 40, 55, 70, 85, 100, 115 and 130 percent of soil moisture deficit and three replications in furrow irrigation. Effects of irrigation levels on yield, water use efficiency, weight of dry matter, plant height, stem diameter, median diameter, length and weight of corn were significant. Different levels of irrigation had no significant effect on seed oil and protein content, but their impact on plant fiber content was significant. With increasing depth of irrigation, stem length, grain weight and plant fiber content increased. The minimum and maximum corn yield were related to 40 and 130% of full irrigation with the yield of 43.1 and 88.1 tons per hectare, respectively. The maximum and minimum use efficiencies were 55 and 130% of full irrigation treatments with values ​​of 16.17 and 10.1 Kg per cubic meter, respectively. The result of economic analysis showed that the water consumption is 5/582 mm, equivalent to 86% full irrigation depth.