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Mohammad Reza Yazdani; Ebrahim Asadi Oskouei; Asghar Rahmani; Naser Davatgar; Bahareh Delsouz Khaki
Abstract
In order to analyze the temporal and spatial changes in the amount of water required for puddling in rice fields of the Sapidroud Network, daily soil moisture data from the SMAP satellite was obtained and used in a seven-year period (2015 to 2021). The puddling stage (from April 20 to June 10) was analyzed ...
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In order to analyze the temporal and spatial changes in the amount of water required for puddling in rice fields of the Sapidroud Network, daily soil moisture data from the SMAP satellite was obtained and used in a seven-year period (2015 to 2021). The puddling stage (from April 20 to June 10) was analyzed after grouping based on different probability of occurrence (1%, 10%, 25%, 50%, 75%, 90% and 99%) and using raster calculations. In addition, in order to validate the calculations, the predicted values were compared with the saturated soil moisture values of 321 soil samples with specific geographic coordinates that had been measured by the Rice Research Institute of Iran. The comparison was conducted by using the mean absolute error (MAE), mean bias error (MBE), and normalized root mean square error (NRMSE). The results showed that in all moisture scenarios (from the wettest to driest), the foothills had less moisture than the plain and, especially, the low lands, and the soil moisture showed a decreasing trend during the growing period. The rate of this reduction increased gradually and in some areas it reached 2% per day at the end of the puddling period (May 22 to 31). The amount of gross water required for puddling increased from the wettest to the driest year and in the middle of the season (May 3 to 5) it was from 1693 to 2983 square meters per hectare and at the end of the season from 2496 to 3602 m3/ha, respectively. The validation results showed that the calculated MAE, MBE, and NRMSE values were 4.26%, 1.59%, and 15%, respectively, indicating that the accuracy is acceptable. The findings showed that the delay in the start of the puddling operation increases the water required for puddling operation (1.34 m3/ha for each day delay in a normal year). Therefore, in the lands of this network, in all circumstances, especially in dry years, to save water, it is better to release/supply water required for puddling from local reservoirs, wells, or from the Sepidroud Dam in early May.
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Mohammad Reza yazdani; Hadis Sadeghi; Ebrahim Asadi Oskouei; Saeedeh kouzegaran; Bahareh Delsouz Khaki
Abstract
Changes in evapotranspiration values of rice plants in non-northern regions of the country were estimated for three different planting dates (early, on time and late planting) and with four different probabilities of 75%, 50%, 25%, and 10% (years with low, medium, high, and very high evapotranspiration, ...
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Changes in evapotranspiration values of rice plants in non-northern regions of the country were estimated for three different planting dates (early, on time and late planting) and with four different probabilities of 75%, 50%, 25%, and 10% (years with low, medium, high, and very high evapotranspiration, respectively), using the Penman-Monteith Equation and meteorological data of 15 stations with a statistical period of 30 years (1990-2020). The crop coefficient of rice in different stages of growth were calculated as an average in 10-day periods based on the Weibull Model. The results showed that, in all non-northern climatic regions, adopting an early planting strategy leads to a reduction in water requirement in all evapotranspiration scenarios. Adopting early planting strategy in years with very high evapotranspiration reduces the water requirement of rice in hot, cold and temperate regions by 125.9, 113.5, and 115 mm, respectively, during the growing season (on average 0.7 to 9. 0 mm per day) compared to late planting. However, in cold and temperate climates, there was no big difference between early planting and timely planting and even late planting. So, it is better to use late planting to avoid the possibility of late frosts. Comparison of the results of evapotranspiration rate of rice plant in all planting dates and different probability levels in cold, moderate, hot and very hot climate regions showed that the highest evapotranspiration rate is related to the hot region at the rate of 1021, and moderate and cold regions have much lower evapotranspiration rate than hot regions with evaporation rates of 784.8 and 729 mm, respectively. Therefore, considering the lack of water resources and the negative effects of climate change in arid or semi-arid regions such as Iran, it is better to avoid rice cultivation in hot regions, especially in years with high evapotranspiration. Also, it is better that in cold and temperate regions, the type of irrigation management and the design of structures and water systems should be adapted to the calculations of years with high evapotranspiration.