مجله پژوهش آب در کشاورزی
سال سی و هفتم شماره 2 (تابستان 1402)

In this study, volume of irrigation water, water productivity, and yield of alfalfa were measured in 300 farms in Zanjan, Fars, Chaharmahal and Bakhtiari, Hamedan, East Azerbaijan, Semnan, Khorasan-Razavi, Isfahan, West Azerbaijan, Central, Qazvin and Kerman provinces under farmers management and surface and sprinkler irrigation, various water sources, different water salinities, soil conditions, and varieties, during the growing season of 2018-2019. The results showed that the difference between average volumes of water applied by farmers, yield, and water productivity, in the studied sites were significant at 1% probability level. The average amount of applied water by farmers was 8502, 8901, 9226, 9459, 11481, 12796, 14311, 14821, 15198, 15916, 18351 and 23920 m3/ha, respectively, and the average was 13284 m3/ha. The dry yield of alfalfa varied from 2500 to 30000 kg/ha with an average of 13841 kg/ha. Irrigation water productivity varied from 0.2 to 4.5 and its average was 1.28 kg/m3. The average irrigation water plus effective rainfall productivity for alfalfa was 1.19 kg/m3. The results showed that the average applied water and alfalfa yield in surface and sprinkler irrigation methods were 15076 and 10653 m3/ha, respectively, (p<1%). These results showed that in sprinkler irrigation method, applied water was 30% less and irrigation water plus effective rainfall productivity was 41% higher. Accordingly, in order to reduce the volume of irrigation water and improve alfalfa water productivity, it is recommended to use sprinkler method in suitable climatic conditions where irrigation water is of good quality and the technical criteria of design, implementation, operation, and economic considerations are met.

Rice is one of the most important summer crops in Khuzestan Province. Due to the severe water limitation, the effect of using strip drip system in the method of direct seeded rice in dry bed was monitored on the yield of common rice cultivars of the province and changes in soil salinity. This research was conducted during 2019-20 and 2020-21, at the Ahvaz Agricultural Research Station on three adjacent plots of land, using split-plot design and randomized complete blocks in three replications. The main factor was irrigation including three levels: daily irrigation, every two days, and three days; and the secondary factor included three cultivars (Red Anbori, Champa, and Daniyal) and one salt tolerant rice line (S2). In the first year, due to the allocation of water outside the cultivation date, the yield of the crop was very low, so, the analysis was done based on the second year. The average volume of irrigation water in the field was measured as 14,800, 15,200, 15,700 and 16,100 m3/ha for, respectively, line S2, Red Anburi, Daniyal, and Champa. The results showed that, in the daily irrigation, the "Red Anburi" local cultivar had the highest yield with 3767 kg/ha and S2 line had the lowest 2541 kg/ha, so that when the irrigation changed from every day to three days, the yield decreased by 56% on average. The highest water productivity was obtained by the "Red Anburi" cultivar (0.25 kg/m3) in the daily irrigation. The reason for this problem can be shown in the monitoring of soil salinity, so that with daily irrigation, the salinity of the saturated extract in all soil layers showed a decreasing trend from 3.77 to 1.8 dS/m. According to the results, use of drip irrigation system would significantly reduce the volume of irrigation water compared to "conventional puddled transplanted rice". This has been an effective strategy in reducing the stress on the water resources of the province and saving the available water to preserve the ecosystem, although significant reduction of rice cultivation area in this province is recommended.

Soil and Water Research Institute (SWRI) has presented NIAZAB system to estimate and determine crops water requirement, water consumption, and irrigation planning at the scale of region, district, and plains in Iran. The current research was conducted in order to use NIAZAB system (including Tafteh, Pasquale and Reas methods) in determining the amount of water used for soybean cv. Williams, based on the inverse solution of the production function. The experimental treatments in this research included no fertilizer and application of of 150 kg N ha-1 and different irrigation treatments including 100%, 80%, 60%, and 40% of water requirement. Experimental design was split plot in the form of randomized complete blocks with three replications, and was conducted in Hajiabad Region, Hormozgan Province, in 2020 and 2021. The values estimated by the system and measured showed that, in the first year, the average relative error (ARE) in eatimation of evapotranspirationin by Tafteh, Pasquale and Reas methods were 7.49%, -0.05%, and 9.14%, respectively. In the second year, these values were 6.47%, -1.29%, and 9.06%, respectively. The ARE in the physical water productivity in the mentioned methods was -8.23%, -0.73%, and -10.08% in the first year, and -7.10%, 0.58%, and -10.07% in the second year, respectively. In Tafteh, Pasquale, and Reas methods, the root mean square error (RMSE) were 43, 35, and 49 mm, respectively, and the normalized root mean square error (RMSEn) were 0.093%, 0.076%, and 0.105%, respectively. Considering the results, NIAZAB system estimated the amount of irrigation water and evapotranspiration with acceptable approximation and it can be used for estimation of water consumption in the studied area.

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.

To compensate for the lack, or inadequacy, of weather stations data, one of the most reliable ways is to use the remote sensing and re-analysis dataset, which provides a suitable model for such areas. In this study, the performance of two data sources, namely, WaPOR and ERA5, was evaluated in estimating reference evapotranspiration at 64 synoptic stations in the Caspian coastal region in Iran, on a daily and monthly basis. To this end, meteorological data of 64 synoptic stations with a 10-year statistical period (2011-2021) was obtained daily from the Iran Meteorological Organization. The field data used included minimum and maximum temperature, relative humidity, wind speed, and solar radiation intensity. Then, evapotranspiration and reference evapotranspiration were calculated using the Penman-Monteith equation and REF-ET software. Finally, the results were compared with the results from the WaPOR and ERA5 data bases. The results showed that, on average, the nRMSE values of the WaPOR and ERA5 datasets compared to the calculated meteorological station data were 29.6% and 29%, respectively, on a daily basis. Also, on a monthly time scale, in more than 85% of the stations, both datasets provided acceptable results. On a monthly scale, the average nRMSE value for both WaPOR and ERA5 sensors in the catchment area was 19%. The rMBE value showed that the ERA5 dataset underestimated the reference evapotranspiration in most of the stations, while the WaPOR dataset overestimated. Given that the error rate of the two sensors is different in over 30 percent of the stations, a suitable estimate of reference evapotranspiration in the Caspian Sea basin area can be obtained by combining the data from these two datasets. The results showed that in the Caspian Sea coastal areas, 34 stations in the WaPOR dataset and 28 stations in the ERA5 dataset showed the minimum error, with two stations showing the same error. Thus, both WaPOR and ERA5 are suitable databases that can be used for hydrological purposes, including estimation of reference evapotranspiration.

In this study, water productivity in six vineyards under surface and six under drip irrigation systems was measured in Zanjan Province, then, the effect of modified irrigation schedule to improve water productivity was investigated in two selected vineyards. The average volume of applied irrigation water in vineyards with surface and drip irrigation systems was 6929 and 5418 m3.ha-1, respectively. Also, the average of water productivity indices, Gross Benefit, and Net Benefit were obtained as 2.9 kg.m-3, 91.5, and 55.4 thousand Rials.m-3 in vineyards with surface system and 3.6 kg.m-3, 112.4, and 59 thousand Rials.m-3 in vineyards with drip system. In terms of water productivity index, drip irrigation was relatively superior to the surface method. In most of the monitored vineyards, the applied irrigation schedule was not in accordance with the net irrigation requirement. The results of the modified irrigation schedule indicated that water productivity could be improved by 24.7%.