فصلنامه حفاظت منابع آب و خاک
سال چهارم شماره 2 (پیاپی 14، زمستان 1393)

Non-uniform distribution which occurs during manual fertilizing is one of the biggest problems of surface irrigation. This issue needs more research in the field of surface fertigation. The aim of this study is to evaluate the roles of slope and fertigation timing in furrow irrigation. Urea fertilizer was used and nitrate was selected to be the reagent ingredient in order to study the distribution of fertilizer. The research was conducted in agricultural research field of Shahrekord University. A completely randomized block design was employed with four treatments and three replications. The treatments were Control treatment (natural slope, fulltime fertigation) and three periods of fertigation that were first half, second half and fulltime fertigation. Slope changes, fertigation duration, soil depth of the sampling and distance from the furrow beginnings effects were studied on nitrate distribution in the soil. The LSD test was used for statistical analysis. The results demonstrated that slope had a very significant effect on nitrate distribution and storage in the soil (P<0.01). Also, Changes in fertigation timing and duration caused variation in nitrate distribution and the second half fertigation treatment had the highest nitrate distribution uniformity and absorption of 1653.53 mg/kg. Studying simultaneous effects of fertigation timing, soil depth and distance form beginnings of the furrows exhibited that they had no significant impact on each other. Finally, slope and fertigation timing were reported to be the effective factors in the nitrate storage and distribution.

The correct determination and prediction of sediment transportation by the river is very important for water resources management, flood reduction and environmental sustainability projects. Analysis of sediment particle size can show important information about the origin, history, transportation and deposition conditions of the sediment. However, this matter has been less considered. This study was therefore conducted at Vaz River located in Mazandaran Province to investigate effects of sand harvesting on morphometric characteristics of suspended sediments at upstream and downstream of the study mine. For this purpose, monthly samplings were made at upstream and downstream of the mine from February 2012 to January 2013. The particle sizes of suspended sediment were measured by Master Sizer and corresponding distribution and specifications including mean, sorting, skewness and kurtosis were also analyzed by the GRADISTAT software package. The range of variations of D10, D50, D90, and average particle size of the study samples were obtained as 0.34-1.12, 3.24-13.41, 14.12-90.74 and 3.19-11.45 microns. In addition, changes of sorting, skewness and kurtosis were found from 3.11 to 6.38, -0.13 to -0.32 and 0.88 to 1.29, respectively. Mines discontinuous activity and distance between study mines and sampling locations could be considered as main factors behind non-significant effects of sand and gravel mining on changing suspended sediment particle size distribution.

Nowadays, the use of wastewater in irrigation of agricultural crops for the protection of water resources and eliminating the water crisis and shortages and also to reduce environmental hazards caused by increased production of wastewater has increased. Drip irrigation system is the best method for using wastewater; however, emitter clogging is the biggest problem with drip irrigation systems. Lateral flushing is one of the appropriate tasks for control of emitter clogging. The objective of this study was to investigate the amount of clogging of PCJ (2 L/h), PCJ (4 L/h), and UniRam (3.5 L/h) emitters in terms of use of treated wastewater and also to determine the effects of lateral flushing on reducing or eliminating emitter clogging. For this purpose, the changes of relative discharge rate, emission uniformity, Christiansen’s uniformity coefficient and the statistical uniformity coefficient of studied emitters for use of treated wastewater and lateral flushing, during the 504 hours of irrigation, were investigated. The results showed that the amount of emitter clogging of studied emitters in terms of use of treated wastewater was not considerable. Generally, PCJ (2 L/h), PCJ (4 L/h), and UniRam (3.5 L/h) emitters respectively with 6.4, 0.9 and 0.5 percent of flow reduction were more sensitive to clogging. Lateral flushing reduced emitter clogging. Additionally, the performance of studied emitters in the indices of relative discharge rate, emission uniformity, Christiansen’s uniformity coefficient and statistical uniformity coefficient during the test was in the range of good to very good.

Soil surface water content is a key variable of hydrologic cycle which plays a significant role in global water and energy balance by affecting several hydrological, ecological and meteorological processes. Soil moisture varies significantly in space and time due to spatial variability of soil properties, topography, vegetation characteristics and atmospheric dynamics. Soil moisture is either measured directly by in situ methods, e.g., Neutron probe, time domain reflectrometry (TDR) or estimated indirectly through pedotransfer functions (PTFs) or remote sensing (RS). Since in situ measurements in large scales are mainly expensive and time consuming, the RS-GIS methods can be used for this purpose. The objective of this study was to estimate surface soil moisture using NDVI, NDMI and LST indices. For this purpose, by using images of MODIS 1B, the indicators of soil moisture were obtained. By using the field soil moisture data, the required analyses were performed to calibrate and validate the model output. The results indicated that there is a reasonable correlation (0.66) between the soil surface moisture and some indices such as NDVI, NDMI and LST. The model validation further indicated that having a mean error of less than about 0.018, the proposed method can predict soil surface moisture reasonably.

Crop models such as AquaCrop can be a useful tool for better management of water consumption. However, these models should be evaluated before applying. In this study, the accuracy of the AquaCrop model in estimating shoot fresh weight and evapotranspiration of Maize in different soil fertilities and soil textures was evaluated. Field experiments were done as a factorial experiment in a completely randomized design with three soil texture treatments (including silty clay loam, loam and sandy loam) and three levels of soil fertility (including without added fertilizer, adding one and two percent of the fertilizer into the soil). The study was conducted in summer of 2012 in Jey and Qahab region in Isfahan. Results of this study showed that prediction of the model for shoot fresh weight of fodder maize was extremely efficient. The normalized root mean square errors (nRMSE) of the shoot fresh weight of fodder maize for calibration and validation stages were obtained as 0.87% and 0.67%, respectively. Predicting maize evapotranspiration during the growing season by the model had a higher error rate. Maximum and minimum of the root mean square error was obtained in the sandy loam soil with the addition of two percent of the fertilizer treatments (SLF2) and loam soil by adding one percentage of the fertilizer (LF1) with values of 0.88 and 1.42 mm per day, respectively. Results of this study showed that the mean values of RMSE and nRMSE in simulating maize evapotranspiration for sandy loam soil were 1.16 mm and 24.3% that were more than mean values of RMSE and nRMSE for silty clay loam soil type and loam which were 1.08 mm, 26.2% and 0.93 mm, 20.4%, respectively. However, the model accuracy in predicting maize evapotranspiration was varied at different levels of soil fertility depending on soil types so that the maximum value of RMSE in the loam soil was obtained in treatment without fertilizer (LF0) and in sandy loam soils in treatment with two percent fertilizer (SLF2).

Sediment yield resulting from soil erosion in the watersheds is the major limitation in achieving the sustainable development and major threat to ecosystems. Therefore estimation of output sediment from watersheds is very important. Extent of watershed and deficiency of sediment measuring stations have caused us to use different indirect methods to estimate sediment, such as the use of models provided in similar watersheds. In this study 42 sediment measuring stations in south and southeast of the Caspian Sea with over 20 year period were chosen. By relating suspended sediment load to stream discharge in the times of flood, daily suspended sediment was estimated by using the daily discharge and the average of annual sediment was calculated. By using the Gamma Test, 13 factors affecting sediment yield were reduced to 5 main factors and by using cluster analysis, discriminate function analysis and andrews curves, study stations were put in homogeneous groups. For each homogeneous group obtained from any one of the mentioned homogenization methods and by using five main factors selected, regression models were developed to estimate the average of annual suspended sediment. Error rates and accuracy of prepared models by using statistical indices of RE, RBIAS and RRMSE were calculated according to observed data. Results indicated that all three homogenous techniques had better results than those of the general model and Andrews Curves with 38.12 and 45.91% RE, 53.16 and 33.11% RRMSE and -0.01 and 0.01 RBIAS in calibration and validation stages, respectively and had better performance than those of two methods i.e. Cluster Analysis and Discriminate Function Analysis for homogenizing of south and southeaster Caspian Sea watersheds based on sediment yield. Also peak discharge (Qp) has the most impact on the average of annual suspended sediment changes.