Journal of Water Research in Agriculture
Year:2012 | Volume:26 | Issue:2|Papers Count:9

Access to fresh groundwater plays an important role in stable crop production and secure livelihood of people living in the Neyshabour plain. Decline in groundwater table and annual aquifer abstraction of more than 200 million cubic meters are the most important challenges in this plain, where about 110,000 ha of agricultural land are cultivated annually and 96% of groundwater resources are used in the agricultural sector. In this study, Soil-Water-Atmosphere-Plant (SWAP) model was calibrated and validated using measured data from six different fields located in the Neyshabour plain. For this purpose, field information and other SWAP required data were collected in the six farm conditions. Calibrated and validated SWAP model was then used to quantify the effects of existing irrigation practices on water balance components and different water productivity indicators and to determine improved irrigation schedules for wheat, barley, sugar beet, cotton, silage corn, and tomato. Estimation of the net water saving as a result of improved irrigation schedules is also discussed. The results showed that under the current irrigation practices, soil evaporation reduced WPET (Yact/ETact) over WPT (Yact/Tact) by 24%, 26%, 27%, 21%, 8% and 16% for wheat, barley, sugar beet, cotton, silage corn and tomato, respectively. The reduction in WPETQ (Yact/ETact+qbot) over WPET because of deep percolation was even higher: 50%, 44%, 33%, 37%, 14% and 56% for wheat, barley, sugar beet, cotton, silage com and tomato, respectively. The substantial differences in WP values emphasized the need to control non-beneficial soil evaporation and deep percolation losses, and change traditional irrigation system by a more efficient one. Model simulations by improved irrigation schedule revealed that a seasonal irrigation amount of 520 mm for wheat, 440 mm for barley, 1010 mm for sugar beet, 930 mm for cotton, 870 mm for silage com and 1050 mm for tomato would be enough to get the maximum yields. The optimized irrigation schedule uses 26% less irrigation water as compared to current irrigation practices and increases WPI (Yact/1rrig) by a factor of 1.2 for wheat, 0.7 for barley, 1.6 for sugar beet, 6.7 for silage com and 8.3 for tomato because of reduced soil evaporation and moisture storage in the root zone. Considering the total area of cultivation of the six studied crops in the Neyshabour plain (80000 ha), it is estimated that adoption of optimal irrigation schedules can save up to 165 million m3 of water.

In order to investigate the effects of deficit irrigation during phenological stages of fruit growth and development on almond (cv. "Marnaei") production, an experiment was carried out in split plot and complete randomized block design with three replicates in 2000-2003.The main plots were three different stages of fruit growth consisting of: stage I (fruit growth), stage II (kernel growth) and stage III (pre-harvest period). The subplots were different irrigation regimes including T1=100% ETC (Full irrigation), T2=80% ETC (deficit irrigation), T3=40% ETC (deficit irrigation), and T4=0% ETC (without irrigation). Parameters such as fruit size (length, width, and diameter), fresh and dry fruit weight, fresh and dry kernel weight, fruit drop, kernel percentage and yield were measured. The results showed that deficit irritations and water stress during stage- I decreased fruit size (length, width and diameter of fruit), fresh and dry weight of fruit and increased fruit drop percentage; but it did not have significant effect on mineral elements in leaf and fruit. The deficit irrigation and water stress during stage-II decreased fresh fruit weight, fresh and dry kernel weight, N in leaf and B in fruit. However, there was no significant effect on the measured parameters during stage-III. According to the results, deficit irrigation during all phenological stages of fruit growth significantly decreased yield, kernel dry weight and kernel percentage. The results showed that the effects of phenological fruit stages on N, K, Ca and B in leaf and on N, K, P, Mg, Ca, Zn, Fe, Mn, Cu and B in the fruits were significant, but the effects of irrigation regimes were not significant on mineral elements in leaf and fruits.

Population growth has resulted in increase in water use, which in turn has led to a decline in quantity and quality of ground waters. Therefore, quantitative and qualitative assessment of groundwater resources is crucial for sustainable agriculture. This research was conducted to evaluate the spatio-temporal variation (1S years) of groundwater table and the quality of groundwater resources of Darab plain. To this end, data of39 piezometers in the plain were selected to evaluate the groundwater table fluctuations during an IS-year period, while qualitative characteristics were determined for 200S- 2012. Results showed that the mean groundwater level depletion was 27.23 m during the studied period. Also, qualitative dynamics indices of water showed that EC, pH, and nitrate of the groundwater increased annually during the study period. Overall, the water budget of the region, the lowering of water table, and the increase in water salinity and acidity indicate the unsustainability risk of the ground water of the studied region.

Speed and direction of wind affect water distribution pattern of sprinkler irrigation system. Based on an acceptable water distribution uniformity range, distribution pattern of any single sprinkler under different wind conditions is needed to determine the best sprinklers arrangement. In this study, water distribution of NELSON-F80AP sprinkler was assumed to be a function of the Beta probability distribution and influences of wind speed and direction on the distribution pattern were studied. Similar to common sprinkler irrigation systems, a single sprinkler (NELSON-F80AP model) with wetting radius of 22.86 m and application angle of 360o was set at about 1 m height from land surface. According to the operating pressure in the irrigation system, 40 psi pressure was applied during the experiments. Firstly, Beta distribution function parameters were calculated on the basis of the measured water distribution pattern under controlled (no wind) condition. Then, the change of distribution pattern due to different conditions of wind and its relevant suitable probability function parameters for each condition were determined. The water distribution pattern uniformity was fair and a good fitness between the calculated and observed data was obtained in the wind speed range of 0-3 m/s. The relative error was less than 3.53% in this case. In the speed range of 3-6 m/s, the distribution pattern uniformity was poor and the relative error was raised up to 4.65%. For the wind speeds greater than 6 mis, relative error between the calculated and measured pattern was about 8.48%, because of wind drift and evaporation losses and also the effect of wind on the uniformity of water distribution pattern.

In terms of efficiency and economy of water resources, cultivation of safflower, as an important oilseed crop acclimated to the county's conditions, can be effective. A field trial aimed to evaluate the grain yield and some physiological properties of the new safflower genotypes under drought stress was performed as split plot experiment in randomized complete block design (RCBD) with three replicates in 2010-2011 crop season. Drought stress levels were applied after flowering as soil water potential (-0.5 i.e. the control, -3.5, and -6.5 atm) and allocated to the main plots, while the new safflower genotypes (Sofeh, Goldasht, Mecl2, 411, Mec50, Mec141, C44, Padideh, and Kw2) were planted in the sub-plots. Analysis of variance showed that drought stress had significant effect on thousand grain weight, grain yield, photosynthetic pigments, leaf relative water content (RWC) and proline content. By increasing drought stress, the content of photosynthetic pigments, thousand grain weights, and proline increased, but leaf relative water content and grain yield decreased. The highest and the lowest grain yields belonged to Goldasht and Kw2 genotypes, respectively, and Mec141 was the best selected genotype tolerant to drought stress. Correlation between thousand grain weight, grain yield and proline content was significant, which reflect their importance in increasing grain yield.

Deficit (or regulated deficit) irrigation is one way to improve efficiency of water use when crop is exposed to a certain level of water stress during a particular growth period. In order to optimizing water use under tape irrigation system, a field experiment was carried out during 2010 growing season at the experimental farm of Agriculture and Natural Resources Research Center of Orzoueyeh, located in Kerman province. The treatments were laid out in completely randomized block design with three replications., Four water potential thresholds for starting the irrigation treatments were selected by using tensiometers (net water requirement (control) and suctions of 1.2 FC, 1.5 FC and 1.8FC). The crop studied was com, single cross 704 cultivar. The results showed that water use volumes saved in the three suction treatments consisting of treatments 1.2 FC, 1.5 FC and 1.8FC were 11%, 13% and 17 percent, respectively, in comparison with the control treatment. But, compared to the control, yield of the mentioned treatments decreased by 4%, 28%, and 34 percent, respectively. However, water use efficiency increased in the 1.2 FC treatment by 6.5% over the control treatment. Statistical analysis of yield components in the control and 1.2 FC treatments demonstrated that these two treatments were in the same group. Among the evaluated treatments, the control and 1.2 FC treatments were economically satisfactory.

Drought stress is one of the most important factors that limit plant growth in arid and semi-arid region such as Iran. By application of super absorbent, rain water can be saved in this region, thereby improving soil physical conditions and, consequently, reducing water stresses for plants. This research was performed as a factorial experiment with completely randomized design and 3 replications to evaluate the effects of stockosorb super absorbent and irrigation on atriplex growth and some soil physical properties. The treatments included S levels of super absorbent (0, 0.1, 0.2, 0.3 and 0.4 % w/w) and 3 irrigation intervals (daily, every 3 days, and every S days). The results showed that application of super absorbent had positive and significant effect on plant indices including height, wet and dry weight of shoots, wet and dry weight of roots, and root length (p<0.05). All indices had the highest values in the treatment consisting of 0.4% super absorbent and 3- days irrigation interval. In addition, application of super absorbent resulted in improved soil physical properties, so that due to super absorbent application, saturated and plant available water contents increased, but bulk density and electrical conductivity decreased significantly at p<0.05. Considering the results of this study and the limited water supply for plants in arid and semi- arid regions, application of 0.3% super absorbent in combination with 3-days irrigation interval can be recommended as a successful method to retain moisture and to increase atriplex growth.

When irrigating with saline water, salt distribution pattern within the root zone is affected by leaching fraction and crop water uptake pattern, in addition to the chemical interactions of soil solution. In order to evaluate leaching requirement and sensitivity of alfalfa to salinity, a lysimetric study (cylindrical lysimeters with internal diameters of 40cm and height of 180 em) was conducted in completely randomized design with 3 levels of irrigation water salinity (3, 7 and 13 dS/m) and 3 levels of leaching fractions (12%, 25%, and 50 %) as a factorial experiment with 4 replications. After packing, soil columns were leached until drainage water salinity reached 3 dS/m and, then, were sown with alfalfa (Yazdi cultivar). To prepare different irrigation water salinity, natural saline water from Sadouq Salinity Research Field with salinity level of 14 dS/m was blended with tap water in different ratios. The amount of applied water was based on crop water consumption in addition to leaching fraction which was carefully weighed. The collected drain water was weighed again after 48 hr in which drain water quality was measured too. The least required irrigation cycles to reach steady state conditions was 12 cycles which increased with increasing salinity level and decreasing leaching fraction. Generally, results showed that implementation of a defined leaching fraction can reduce soil salinity more than WatSuit predictions. Therefore, soil salinity control at a desired level can be obtained with less leaching fraction level. This is especially important for optimum water utilization under saline conditions when irrigation is linked to application of more salts.

Use of Surface Energy Balance Algorithm for Land (SEBAL) and satellite imagery is a relatively new procedure for estimation of actual ET at different scales e.g. farm, catchments and basin levels. This method is based on computation of latent heat flux as the residual of energy budget equation (LE=Rn-G-H) and is now used widely around the world, including Iran, for computation of evapotranspiration under standard and non-standard conditions. Azadegan plain is one of the plains that is now faced with waterlogging and salinity problems due to its special topographic, climatic, and hydrologic situations and also due to improper management of its water and soil resources. The main objective of this study was to use the SEBAL to calculate actual ET (ETa) of winter wheat in 2007-2008 cropping season. For this purpose, a seasonal time series of 19 MODIS satellite images and also ancillary climatic data were acquired and used. Finally, time series of daily ET a maps and also a seasonal ETa map were generated and analyzed. Since the crops of the region are under salinity stress, the calculated ETa is an explanatory of crop water requirement under non-standard conditions. The results could help in advising a proper water management plan and also strategies for control and management of salinity and water logging in the region.