R. Chamani; M. Azari
Abstract
Introduction: Over the past decades, millions of hectares of high-quality lands have been converted to other uses and low-yielding agriculture, which have had some unpleasant consequences for watershed hydrology. Analysis of hydrological responses of different basins to land use change has shown that ...
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Introduction: Over the past decades, millions of hectares of high-quality lands have been converted to other uses and low-yielding agriculture, which have had some unpleasant consequences for watershed hydrology. Analysis of hydrological responses of different basins to land use change has shown that correct land use balances the hydrological status of the basin, so that land use and the type and density of vegetation play an effective role in permeability and runoff reduction by changing humidity, soil organic materials and soil structure. Dimensions of hydrological effects of land capability in Chehel chay watershed in Golestan province, which is affected by land use change and deforestation, are more important. Therefore, this study seeks to investigate different scenarios of land use change and its effect on the hydrological status of the basin.
Materials and Methods: The J2000 hydrology model was used to simulate the hydrology of the basin. To better investigate the spatial and temporal variations of the hydrological parameters of the study area, it is divided into 2013 hydrological response units. After calibrating the J2000 hydrological model, the model was fed by rainfall data (1992-2014) and land use potential.
Results and Discussion: To evaluate the performance of the model, the dataset obtained in the time period of 2002-2014 was used for selection simulation and the first nine-years was considered as the calibration period and the remaining was considered as the validation period. The R2 of 0.67 and 0.55, and NAS coefficients of 0.83 and 0.76 were found in the calibration and validation periods, respectively. According to the ranking of Moriasi et al., the model efficiency is "good" and can be used in the present study. Several studies with similar observational data have reported similar results. The results showed that in summer and in May and June, the emptiest space in LPS soil pores is 3.07 and 3.21%, respectively. Increasing the consumption of MPS soil pores has also increased, and from 0.5 to 1.69% of the empty pores in the average soil pores has increased in these months. Therefore, increasing water storage in LPS pores in the months of May to June, surface runoff (RD1) decreased within the range of 6.28-26.38%, and the range of subsurface runoff (RD2) reduction was 4.41-8.41%. The amount of water percolation into groundwater aquifers was positive, and the highest infiltration into groundwater ranged from 0.83 to 1.72% for fast section groundwater (RG1), and from 0.48 to 0.52% for groundwater. Large pores do not hold much water, and water is transferred vertically to medium pores under gravity. When medium pores are saturated with water, water does not penetrate into these pores and remains in large pores and moves horizontally, increasing the subsurface flow. The results indicate that deforestation in order to expand agricultural lands and inappropriate use of the lands are the most important problems. Moreover, population growth has exacerbated the condition, necessitating proper land use management and planning. The scholars have also stated that proper land use has important effects on the water balance of watersheds.
Conclusion: In this study, the hydrological effects of land uses on the hydrological situation in Chehel chay watershed have been evaluated by simulations of the hydrological model. Our results reveal that the unplanned land use changes, land clearing, and expansion of agricultural lands have intensified the hydrological situation of the basin. The peak discharge of surface and subsurface runoff in hydrological response units decreased and the rate of water infiltration into soil and groundwater increased. Reduction of surface and subsurface runoff has also decreased the discharge in the basin outlet.
saleh mahmoom salkovyeh
Abstract
Introduction: Deficit irrigation is a management strategy for increasing water productivity. The yield loss can be compensated by saving water consumption under deficit irrigation. Increasing water productivity is a key factor in removing the biggest challenge facing the agricultural sector in water-limited ...
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Introduction: Deficit irrigation is a management strategy for increasing water productivity. The yield loss can be compensated by saving water consumption under deficit irrigation. Increasing water productivity is a key factor in removing the biggest challenge facing the agricultural sector in water-limited areas, which means less water production. In order to achieve this, awareness of the relationship between water and yield, known as production functions, can be of great help in this regard.
Materials and Methods: An experiment was carried out on a plot of 96 × 30 × 30 m2 based on a plot in a factorial arrangement in three replications. The main treatments consisted of six main hydrothermal treatments (0%, 33%, 66%, 85% 100% and 125% water requirement) and sub-treatments including four levels of fertilization (0%, 33%, 66% and 100% fertilizer requirement), and two cultivars named Golestan and B 557. Furthermore, the irrigation planning based on soil moisture discharge ranged from 5% to 70%. In this experiment, single branch sprinkler irrigation system was used, therefore 144 plots (6 water × 4 fertilizers × 2 digits × 3 repeats) were, created on the sides of the pipeline. On each cropping line, 20 cm spacing on each row and at a row spacing of 75 cm were cultivated. For each plot, the dimensions were 2.5 × 2.3 m (2.5 m in the direction of irrigation, and 3 m along the irrigation line). Soil samples were collected from each depth of 0-5, 20-20, 20-40 and 40-60 cm before each irrigation. The moisture content was determined by weighing method. Based on the physical properties of the soil (bulk density, percentage of moisture content in field capacity and wilting point), effective depth of root and field management (MAD) 60-70% (based on previous studies), the depth of irrigation water was calculated. 40% of N-fertilizer application was carried out prior to sowing and the remaining N-fertilizer was applied from flowering stage with first irrigation and based on different treatments. The irrigation time was determined by dividing the irrigation water depth by the intensity of the sprinklers. 6I treatment due to the close proximity to the sprinklers received the largest amount of water and treatment 1I received the lowest amount of water (rain) as it was situated outside of the spray nozzle radius. From the beginning of planting, the irrigation program was carried out according to the amount of soil moisture at the irrigation time of the 5I treatment (100% water requirement). Therefore, it is expected that treatment 6I has received water more than water requirement. The total amount of water received by each row of crops during the growth period was measured by placing a water collecting canal mounted on a tripod to a height of 1 meter. After irrigation, by using cylinders the depth of water collected in the cans was measured. Due to wind blowing during the day, irrigation was carried out at night, to maintain the uniformity of water distribution. The final harvesting operation was performed for all treatments and replicates on first and second of November. a relationship and the corresponding regression coefficients were obtained between the irrigated yield and the each cultivar and fertilizer level separately, .
Results and Discussion: The quadratic relationship was determined between the yield and the applied water. The coefficients values of the quadratic equation of production function were calculated for each fertilizer application and cultivars and were showed in Tables 5 and 6. The yield functions of cotton cultivars versus applied water were in the form of a second-order quadratic with a downward contraction. Initially, the gradient of the graph was high and then its intensity decreased indicating that water efficiency is much higher in irrigation. In addition, by increasing the amount of irrigation, the amount of the product reached to the peak value, and since then, a yield reduction was observed as applied water amount increased owing chiefly to N-leaching. The sensitivity coefficients for Golestan cultivars and 557 B were calculated at four levels of fertilizer according to the Doorenbos and Kassam formula. The average sensitivity coefficient for Golestan and B-557 was 1.18 and 1.27, respectively.
Conclusions: It can be concluded that the Golestan cultivar is less sensitive to water shortage as compared with B-557. These results can be used to optimize water use under water constraints.
