محمدمهدی نخجوانی

Providing food security in scarcity conditions of water resources requires macro-planning for the supply, allocation and water consumption in different sections such as agricultural section. In Iran, like in other countries of the world, most fresh water resources are consumed in the agricultural sector. In this situation, one of the effective and practical solutions is the optimal use of irrigation water in the agricultural sector, which consumes the most water. The most basic component for optimal irrigation water management in Iran is the awareness of applied water in the production of various agricultural products under the farmers’ management conditions. Therefore, this study was conducted with the aim of appraising irrigation water management indicators such as seasonal applied water, yield , and irrigation water productivity, total water productivity (irrigation water plus plus effective rainfall ) in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces as peach and nectarine production hubs in Iran.

In this study, a field survey was conducted to measure applied irrigation water and yield under the gardeners’ management in peach and nectarine production hubs. This indicators was measured in 195 gardenes in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces with different conditions of climates, irrigation methods (surface and drip), salinity of irrigation water and soil; and different peach and nectarine cultivars during growing season 2018-2019. To measuring irrigation water volume, after determining the inflow of water to the garden by carefully monitoring the garden irrigation time and measuring the irrigated area, the volume of irrigation water applied by peach and nectarine trees in each garden was measured. Crop yield was obtained in three consecutive years and their mean was used in the analysis. Irrigation water productivity (WPIrr) and total water productivity (WPIrr+pe) were calcucated as the ratio of yield to applied water and irrigation water plus effective rainfall, respectively. Then, the effect of modern irrigation methods (surface drip irrigation) on applied water, WPIrr and WPIrr+pe were investigated in the study areas. Analysis of variance was used to investigate the possible difference between yield, applied water and WP among the hubs. Data adequacy was assessed by using the method provided by Sarmad et al. (2001)

The results showed that the difference between average volume of water applied by gardeners, yield, WPIrr and WPIrr+pe, in the studied sites were significant at 5% probability level. The average amount of applied water by gardeners in Azarbayjan Sharghi, Azarbayjan Gharbi, Ardabil, Alborz, Tehran, Chaharmahal and Bakhtiari, Fars, Qazvin, Markazi, Hamedan, Golastan and Mazandaran provinces was 8617, 7178, 8140, 8137, 8568, 7763, 8814, 8675, 10806, 6428, 2842 and 2012 m3/ha, respectively, and the average was 6734m3/ha. The yield of peach and nectarine varied from 10 to 50 tons/ha with an average of 20 tons/ha. Irrigation water productivity (WPIrr) varied from 1.6 to 8.6 and its average was 3.06 kg/m3. The average WPIrr+pe for peach and nectarine was 2.44 kg/m3. The results showed that the average applied water for peach and nectarine orchards in the study areas except for Golestan and Mazandaran provinces for surface and drip irrigation methods were 9325 and 7098 m3/ha, respectively, (p<1%). Therefore, in drip irrigation method, applied water was 25% less and WPIrr was 34% higher.

In general, the results of this study provide useful information on irrigation water management indicators in peach and nectarine production to managers and water decision makers within Iran. Accordingly, in order to reduce the volume of irrigation water and improve peach and nectarine water productivity, it is recommended to use drip irrigation 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. Also, training and application methods to improve the performance of surface irrigation to reduce evaporation and applied irrigation water is recommended.

Providing food security in scarcity conditions of water resources requires the optimal management of irrigation water. Estimation or determination of indices of water consumption management, such as water productivity in agricultural productions is one of the most important key in macro-planning for the supply, allocation and consumption of water in different sections such as agricultural section. Therefore, conducting a research at the national level that can lead to the real water productivity in the horticultural production in Iran, is essential and important. According to the production (3.4 million tons), a significant amount of surface and groundwater resources are consumed for apple production. This research was conducted with the aim of determining the amount of consumed water in apple orchards in selected provinces under the management of gardeners at the national level. Findings of this study could assist to the decision on management of water and agriculture.

The selected provinces were East Azarbaijan, West Azarbaijan, Ardabil, Isfahan, Tehran, Khorasan Razavi, Fars and Semnan. The water productivity in 145 sites was estimated, in addition to direct measurement of water consumption and crop yield. The factors such as irrigation systems, apple cultivars, gardeners' education, soil texture; and salinity of soil and irrigation water were also measured or recorded in apple orchards. The ANOVA was used to investigate the possible difference between the volume of consumed water, yield, and water productivity in apple production.

The results showed that the difference between the volume of water consumption, crop yield and water productivity was very significant in the orchards from provinces. The volume of consumed water and crop yield in apple orchards over the country averaged 9814 m3 ha-1 and 23.2 t ha-1, respectively. The water index was 2.73 kg m-3 in apple orchards over the country. The lowest and highest water productivity were obtained from the orchards of Fars and Semnan provinces.

Some strategies have been proposed to optimize the consumption of water resources; and to improve apple yield and water productivity in the country's level. The results of the research in apple orchards of selected provinces in Iran revealed that average of water consumption in apple orchards were 9814 m3 ha-1 with the water productivity of 2.73 kg m-3. Application of high-efficiency and well-managed irrigation systems, and other appropriate improving methods of water productivity can lead to optimal use of water resources, improve yield and enhance water productivity in production.

Today, one of the most important challenges of the present and the future, especially in the arid regions of the world, is the issue of water shortage and in some cases the water crisis. One of the ways to improve water productivity and better water management in agricultural sector as the largest consumer of water is the use of super-absorbent materials to improve soil texture, increase soil water retention, reduce erosion and increase germination. The aim of this study is to evaluate the effect of Aquasource superabsorbent polymer on physical parameters and soil-water characteristic curves (SWCC) of different soil textures.  

Aquasource is a new generation of potassium-based superabsorbent polymers that are biodegradable and free of destructive acrylamide compounds. In order to evaluate the effect of Aquasource hydrogel on hydro-physical properties of soils, some experiments in the form of a completely randomized design with 3 replications was performed. The first factor was different levels of superabsorbent (0, 0.5, 1 and 2% by weight of superabsorbent/soil) and the second factor was three different soil textures (sandy-loam, clay-loam and silty-clay). SWCCs related to all treatments were determined by determining the moisture content of the samples at different pressures (0, 0.3, 0.5, 1, 3, 6, 9 and 15 bars) using a pressure plate device. Then, to obtain the soil moisture characteristic curve parameters  in each sample, two softwares RETC (v.6.02) and Rosetta (v. 1.1) were used.  

The results of variance analysis and mean comparisons based on Duncan's test showed that in all soil textures studied, the application of superabsorbent and the increase Aquasource amounts, increased the moisture contents at the field capacity and permanent wilting point. However, the highest amount of soil available water for plant use in sandy loam, clay loam and silty clay textures was 9.8%, 13.8% and 12.7%, respectively, and they are related to the use of 0.5% w/w of superabsorbent in these treatments (Fig. 1). The use of larger amounts, up to 2%w/w, reduced the soil available water for plant use. This issue can be related to the reducing the interaction of soil particles and polymers with increasing the amount of superabsorbent application in soil. At high levels of superabsorbent consumption, the contact of the hydrogel with the soil particles is reduced, followed by the aggregation of the superabsorbent. This prevents the proper exchange  between the superabsorbent and the surrounding soil, and thus despite the presence of moisture in the soil-superabsorbent system, this moisture cannot be used for the plant, so that in all three soil textures the lowest amount of plant available water belongs to the treatments of 2% w/w of Aquasource. The results of statistical analysis for estimating the parameters of the soil-water characteristic curve due to the application of different levels of superabsorbent in different soil textures using two software RETC (v.6.02) and Rosetta (v. 1.1) showed that the fit The Van-Genuchten (Moallem) model in RETC software in all treatments has provided a good approximation of the parameters of the soil-water characteristic curve (R2> 0.98). Also, with increasing the amounts of superabsorbent, the accuracy of the model in estimating the parameters decreased to some extent.    

Application of Aquasource superabsorbent and increasing the application level of this superabsorbent polymer (from 0 to 2% by weight of superabsorbent/soil) in sandy-loam, clay-loam and silty-clay soil textures caused an increase in the moisture content at field capacity and permanent wilting point. Application of 2% W/W in sandy-loam, clay-loam and silty-clay soil textures increased the moisture content at the field capacity by about 2.4, 1.6 and 1.5 times, respectively, compared to the control treatments of each soil textures. However, the highest amounts of plant available water in all three soil textures were obtained by applying 0.5% W/W (superabsorbent/soil). Application of 0.5% W/W in sandy loam, clay loam and silty clay textures increased the plant available water by about 1.23, 1.19 and 1.12 times compared to the control treatments in each soil textures, respectively. However, the use of larger amounts reduced the plant available water. At low levels of Aquasource application, the interaction between the   superabsorbent polymer and the soil particles in the soil/polymer system facilitates the transfer of moisture stored in the superabsorbent to soil particles. However, increasing the application level of this polymer up to 2% W/W has an inhibitory effect and in this case, the interaction between the polymer and soil particles is reduced, which leads to a lack of proper drainage of moisture from the polymer.   Acknowledgement The authors would like to thank Agricultural Engineering Research Institute for supporting this research.