نشریه دانش آب و خاک
سال سی‌ام شماره 4 (زمستان 1399)

Tillage can significantly influence the productivity and sustainability of modern farming systems. In addition, the chemical nature of soil P is affected by tillage practice. The aim of this work was to determine changes of inorganic P fractions in a soil (labile, moderately labile, nonlabile, residual) under different tillage managements using Bowman and Cole (1978) procedure. Soil samples were taken from four different tillage treatments {conventional tillage (CT), Raised Bed Tillage (RB), Minimum Tillage (MT) and No-Tillage (NT)} from 0-8 and 8-16 cm depths with a factorial randomized complete block design with 5 replicates. The results showed that the tillage systems had significant effect on total P and all inorganic phosphorous except on nonlabile inorganic phosphorus. The change in soil tillage from conventional to conservation tillage significantly increased the amount of inorganic phosphorus forms (labile P, moderately labile P, residual P).  The most significant variation belonged to in labile inorganice phosphorus, in which the amount of labile inorganic phosphorus in conventional tillage (9.51 mgkg-1) increased to 21.37 mgkg-1 in minimum tillage (MT), indicating an increase of approximately 2 times compared to conventional tillage. No-tillage treatment showed the highest amount of moderately labile P (678 mgkg-1) and the lowest amount (580 mgkg-1) was in conventional tillage. The highest and lowest amounts of total inorganic P (522.95 and 441.98 mgkg-1) were observed in No-tillage and conventional tillage, respectively. The results of this study indicated that the change in soil tillage from conventional to conservation tillagehas considerable effect on soil P reserve.

Drought is a crawling environmental phenomenon that has a major impact on the economy, agriculture and society. This phenomenon is more pronounced in the eastern, central and southern parts of Iran due to its dry and semi-arid climate. According to the fact that the meteorological drought starts by the rainfall shortage, so, the standard precipitation index (SPI) with different time scales (3, 6 and 12 months) are obtained for the Neyshabour synoptic station using the fifth report data. Precipitation synthetic data were determined using the 6 models and the two RCP4.5 and RCP8.5 emission scenarios of the LARS-WG downscaling model. Finally, using the rainfall data, the value of SPI drought index for the base period (1992-2011) and the future period (2020-2039) were calculated in the three-time scales. The results showed that the highest and lowest daily precipitation mean values in the yearly scale for the future period under influence of the RCP 4.5 scenario the Canesm2 and MIROC models and under influenced of the RCP8.5 scenario belonged to the GISS-ES-R and Csiromk-3.6 models, respectively. The SPI values at 12-month time scale showed more drought intensity than the 3 and 6-month periods. The results also showed that under the RCP4.5 scenario the MIROC and GISS-ES-R models and under the RCP8.5 scenario the Canesm2 and MIROC models estimated a greater number of dry years.

In order to reduce evaporation from the soil surface and to increase the water use efficiency in maize, a research was conducted as a factorial experiment based on the randomized complete block design with three replications at the experimental field of Faculty of Water Engineering, Shahid Chamran University of Ahvaz in 2016-2017. The experiments were carried out using three levels of irrigation (application 100, 80 & 60 percent of the crop water requirement) and two types of tubes (with a plastic mulch cover having the width of 40 cm [winged tape] and without cover [tape without wing]). Significant interactions were observed between irrigation and moisture levels in some parameters such as number of leaves, stem fresh and dry weight and 100-seed weight, although no significant interaction were observed among the other parameters. The maximum grain yield was obtained in treatment with 80% water requirement with average weight of 13650 kg ha-1, however, it had no no meaningful difference with 100% water requirement treatment. The maximum water use efficiency was observed in treatment of 60% water requirement, with 2.81 kg/m3. Between irrigation methods, the winged method increased 13% both of the grain yield and water use efficiency compared to those with the non-winged method of irrigation in this study, which can be attributed to the reduced evaporation from the soil surface.

So far, the linear time series parameters are estimated, generally based on graphical and approximate methods. Therefore, the use of a new approach to increase the speed and ease of access to the best time series model can play an important role in using this method for predicting hydrological events. In this research, an optimization approach based on genetic algorithm has been used to estimate the ARMA time series parameters. A hybrid of Genetic Algorithm-ARMA method was used to drought prediction at three selected stations in the Urmia Lake basin, including Tabriz, Saqhez and Urmia, based on the SPEI drought index. The results showed that according to the BDS test, the model had the ability to predict the drought in all three stations and in all time scales. The Ljung-Box statistic was also used to evaluate the reliability of the prediction model. Its p-value at all stations and time-scales were greater than 0.05 which indicated the residuals of models were random and reliable. Also, the best time series model was calculated at different time scales and based on this, the SPEI index was predicted. The results of the prediction section showed that ARMA-GA hybrid method had a high accuracy at all long-term time scales of SPEI index at all the stations, but its performance was not suitable for short-term time scales.

The aim of this study was to investigate the chemical forms of Pb, Zn, Cd, and Cu in two concentrations and three pH values in a calcareous soil. Metals as nitrate salts were added at two levels of 1.0 and 10 mmol kg-1 for Pb and Zn and at two levels of 0.1 and 1 mmol kg-1 for Cu and Cd all at three levels of pH (6, 7 and 8). The soil to solution ratio (w/v) was 1 to 20. The soils were incubated at 30±1°C for 30 days. Chemical forms of metals in the soils were determined by Tessier method. The results showed that the distribution of native forms of Pb and Zn was independent of pH. With increasing pH values from 6 to 8, the residual form of Cu decreased, whereas its organic form increased. Regarding the limit of quantitation (LOQ) for the atomic absorption instrument, the native cadmium was not measurable. The effect of pH on metal distribution between different forms varied with respect to metal nature and its concentration. The oxide and organic forms were dominant in low concentration of Pb and the oxide and carbonate forms were dominant in high concentration of this metal. Moreover, the added Zn and Cu were mainly dominated in oxide and organic forms, respectively. The added Cd was accumulated in organic form at low concentration and accumulated in exchangeable form at high concentration.

Sedimentation is one of the important phenomena in water engineering due to its effect on the transport capacity and hydraulic performance of water transport structures. As there are numerous factors that affect this phenomenon, it is difficult to accurately determine the most influential parameters. In the present study, the efficiencies of intelligent Gaussian Process Regression (GPR) and Adaptive Neuro-Fuzzy Inference System (ANFIS) approaches in the prediction of sandy sediments in circular pipes with rough and smooth beds have been evaluated. Using several series of laboratory data, different models were defined with considering the impacts of hydraulic parameters and sediment particle characteristics and evaluated for rough and smooth pipes. The results showed a high accuracy of the methods used in the present research. According to the results in estimating the sediment load in circular pipes using only hydraulic parameters did not lead to accurate results, and the properties of sediment particles also affect the estimation process of this parameter. With performing sensitivity analysis, it was observed that the particle's Froude number is the most important parameter in the estimation of sediment load in circular pipes. Also, the results showed that the bed and walls roughness of pipes was effective in sediment transport and the increase of roughness values reduced the accuracy of the results.

The identification of soil fractions minerals types that have different vegetations is a matter of special importance. The aim of this study is investigation of the soil particles’minerals under continues cultivation. Hence, three different regions with similar soil moisture regime (xeric) including Gyan, Doroud and Kangavar plains were selected. Then 13 pedons with different properties and crops’cultivation history were selected and soil profiles were dug and analysed. The selected soils were under cultivation of rice, wheat, canola and sugar beet. Soil samples were collected from different horizons and their physicochemical and mineralogical characteristics were measured in the laboratory. All size fractions were separated and content of minerals in sand, silt and clay fraction was determined. X-ray diffraction, TEM and SEM analysis results from clay fraction in rice cultivation indicated that the most semi quantitative of minerals is sequential: chlorite> vermiculite> smectite> illite. The ponding condition provided a suitable posotion for stability of chlorite and vermiculite minerals. The presence of vermiculite in paddy rice might cause biotite weathering. The most of smectite content was observed in clay fraction in sugar beet cultivation and then in canola cultivation. The neoformation of smectite containing Ca as exchangeable cation was dominant in cultivated soils. The mixed minerals as vermiculite–chlorite, illite- smectite and illite-vermicultie were predominantly observed in silt fraction under rice cultivation and then in sugar beet and canola cultivations. The variability of sand fraction mineral was negligible and it was similar in all cultivation almost.

Groundwater is an important source of exploitation in arid and semiarid regions. In the Azarshahr plain, due to the reduction in annual precipitation and lack of surface runoff, groundwater resources play an important role in supplying agricultural, drinking, industrial and domestic water requirements. The aim of this study was to evaluate the quality of groundwater resources in Azarshahr plain for agricultural irrigation and to analyze the EC and SAR variations by using geostatistical methods. So, for spatial mapping of SO4, Cl, TDS, EC and SAR, the observational data from 47 wells in this region, which were measured during the years 2003-2017, were utilized. In order to select the best interpolation method, Kriging approach with Gaussian variogram and IDW methods were used. The obtained results revealed that the Kriging with Gaussian variogram showed the lowest RMSE and the highest NS values. The results of the groundwater quality classification (using Wilcox diagram) and EC/ SAR zoning showed that the groundwater quality in the Azarshahr plain is very saline (C4S1) in most of the cases, which might be linked to the higher amounts of withdrawals from the aquifer.

Proper management of groundwater resources, as the main source of fresh water, is very important. Groundwater vulnerability assessment has been applied as a management tool for prioritizing the use of resources, controling the contaminant transfer and adopting cost-effective ways for aquifer management. This study has adopted a novel approach based on DRASTIC method, analytic hierarchy process (AHP), and genetic algorithm (GA) optimization method to assess the vulnerability of Shiraz aquifer. AHP was utilized to modify the rank of DRASTIC model’s parameters and GA optimization model was used to optimize the weights of DRASTIC parameters based on hydro-geological characteristics and nitrate concentrations of the Shiraz aquifer. The main aim of the GA-AHP model was to maximize the DRASTIC index correlation with nitrate concentration. The vulnerability map of Shiraz plain was provided using geographic information system (GIS). The results suggested that the southern and southeastern areas of Shiraz plain were faced with very high and high classes of vulnerability, respectively. The Pearson correlation coefficient between the developed vulnerability index and the nitrate concentrations was estimated as 80%, which confirmed the accuracy of the vulnerability map of Shiraz plain.

Soil tillage is an important element of soil management. Tillage type implement depends on factors, such as soil structure, aggregate stability, texture, crop rotation, erosion potential, moisture conditions and time of cultivation. This experiment was carried out with four treatments with three replications as a randomized complete block design. The treatments were tillage with moldboardplough plus rotivator (T1), twice crossover tillage with moldboard plough (T2), no tillage (T3) and once tillage with moldboardplough (T4). Berseem clover was selected as the second cropping production. Soil samples were taken and yield of production was determined after six month. The results showed that mean weight diameter (MWD), geometric mean diameter (GMD), yield of production, penetration resistance, bulk density, porosity and aggregate size in different tillage methods had significant differences. Compare mean showed the minimum of yield and the maximum of MWD, GMD, penetration resistance and bulk density were all related to no tillage treatment, while the maximum yield obtained from T1 treatment. It may be caused by the higher porosity, lower penetration resistance and bulk density and smaller size of aggregates resulted by the rotivator. Result shows that however no tillage method caused the increase of diameter and improvement of aggregate stability, it also caused soil compaction, higher bulk density and penetration resistance, these factors will result in the decreasing of yield. Whereas, the use of moldboardplough and rotivator has the better result than other methods of improvement of soil physical properties and increasing in second cropping of yield production in paddy fields.