نشریه پژوهشهای خاک (علوم خاک و آب)
سال سی‌ام شماره 2 (تابستان 1395)

Environmental problems and instability of agricultural production has caused attracted special attention to those agronomic practices, such as determining the appropriate previous croprotation, management of crop residues, and the optimal use of fertilizers, especially nitrogen, particular attention should be. So, in order to study the effect of rotation (previous crops) and crop residue management on nitrogen application rate in corn (Zzea mays.L cv. SC704) planting and some of the soil chemical properties, this expereiment was conducted in 2008-2012 at Safiabad Agricultural Research Center, Dezful. The experiment was conducted as split- factorial in randomized complete block design with 16 treatments and three replications. Two levels of rotation (canola-corn and wheat-corn) were assigned to the main plots and nitrogen at four levels (0,100, 200, and 300 kg ha-1) and crop residue at two levels (maintaining all of crop residue and complete removal of crop residue) as factorial were randoimized in sub-plots. The results showed that the main effect of rotation on corn grain and biological yields and other traits were not significant. The main effect of nitrogen application had significant effects on corn grain and biological yields, 1000-grain weight, grain protein, nitrogen utilization efficiency, and organic carbon and available phosphorus and potassium after harvesting., Indeed, so that with nitrogen application, the mentioned indices parameters, except nitrogen utilization efficiency, increased. The main effect of crop residue on the studied traits was significant, except grain protein and nitrogen utilization efficiency. The effect of nitrogen and residue management on soil organic carbon was significant. With the increase of in nitrogen application rate and in the treatment maintaininged the crop residue, treatment compared with the removed- residue treatment, soil organic carbon increased. In general, the highest yields of grain (7724 kg ha-1) and biological biomass (14273 kg ha-1) were obtained from maintaining all of crop residue in conjunction with nitrogen application at the rate of ( 200 kg ha-1). Therefore, regarding to the condition of this experiment, application of 200 kg N ha-1 in combination with maintaining of the crop residue is recommended for corn production in this region.

The aim of this research was to study the effects of water stress on nitrogen and growth parameters of corn in a line source sprinkler irrigation system. For this purpose, effects of four levels of 0, 90, 180, and 270 kg N/ha from urea source and four level of irrigation water (6400, 7500, 8800 and 9500 m3.ha-1, I1, I2, I3, I4, respectively) in minimum tillage system were investigated by using a split-block design. In this tillage system, a combined cultivator was used and all tillage and cultivation operations were performed in one step. The results showed that the main effects of irrigation treatments on plant height, stem diameter, fresh yield, concentration and total uptake of nitrogen were significant at (P

The aim of this research was to determine the role of optimum potassium fertilizer usage at phenological key stages of fruit growth in Miyagawa Satsuma mandarin in increasing the relative yield and fruit quality. To this end, potassium soil application (fertigation) and foliar application after fruit set, June drop, and cell expansion were evaluated in randomized complete block design with 5 treatments and 4 replications. Results showed that the highest yield, fruit average weight, and leaf potassium concentration was obtained from K fertigation after fruit set (middle of the first stage of fruit growth) and K foliar application after fruit set in cell expansion stage (second phase of fruit growth). All treatments significantly decreased fruits sunburn percent and increased fruit size and relative grade of fruit size, compared to the control. Potassium foliar application after fruit set and June drop had the maximum impact on relative increase of fruit diameter compared to the control and the percent of larger fruit increased relatively. Also, results showed that foliar application of potassium reduced the number of small fruits and increased medium and large fruits percentages. According to these results, it is recommended that potassium application as base fertilizer (before growth starts) be avoided and soil application begins after fruit set by fertigation; also, split foliar application of potassium nitrate should be done after fruit set and physiological fruit drop (June drop).

Performance of proper method of land suitability for determination of land classes and subclasses for wheat production is very important. This research aimed to determine the quantitative impact of land characteristics on irrigated wheat production, using the theory of fuzzy logic and fuzzy analytic hierarchy process (FAHP) approach. The theory was applied to a land suitability assessment for irrigated wheat in Gotvand, Khuzestan province, southwest of Iran. The methodology was tested by comparing the observed yield and land indices calculated by fuzzy simulation and FAHP approach. Based on the result regression coefficient for fuzzy simulation and FAHP was, respectively, 0.82 and 0.27 and the corresponding standard errors of fit were 252 and 1263 kg/ha. Therefore, the model based on fuzzy simulation had higher accuracy and less error than FAHP. Therefore, fuzzy simulation model is the best method in this research and can be proposed for future study in land suitability evaluation studies.

In recent years, expansion in industrial activities and urbanization has led to accumulation of high concentration of chromium in soil and water resources, which is a serious danger for environment and human health. In this research, potential of Portulaca oleracea in phytoremediation of Cr polluted soil with different chromium concentration was studied. The plants were grown in pots containing soil concentrations of 0, 25, 50, 75 and 100 mg.kg- Cr(in the form of potassium dichromate) in greenhouse condition. At the end of vegetative growth period, concentration of Cr and Cr and also bioaccumulation factors in plant were measured. The results revealed that increase in soil chromium levels led to significant decrease in root and shoot dry matter and concentration of Cr and Cr increased in plant root and shoot. The increase of chromium concentration in soil, especially concentrations of more than 50 mg.kg-, reduced Translocation Factor of Cr in plants. The total chromium concentrations exceeded 3400 and 1500 mg.kg- in root and shoots, in the treatment having 100 mg.kg- of Cr in soil. Bioaccumulation factor in P. oleracea reached a value more than 1, which confirmed the role of p. oleracea as an effective Cr accumulator in soils.

In the recent years, frequent droughts and construction and operation of different dams in the Sepidroud River watershed have markedly decreased water quality (increase salinity) and quantity of the river which is the most important water supply resources in Guilan province. It is predicted that in the next years, due to increasing intervals between irrigations, crack development will be inevitable due to the type of clay and its high content in Guilan paddy soils. Therefore, the loss of water in cracking soils is going to be considered as one of the most important problems. Besides, increase in irrigation water salinity affects soil physical properties associated with the soil shrinkage and crack developments. In this study, shrinkage cracking processes were investigated in laboratory using paddy soils, in the absence of rice plants, with 2, 3, 4 and 5 dSm-1salinity levels using shrinkage characteristic curve. The results showed that change in soil volume started with vertical subsidence and crack initiated at a moisture content almost close to saturation (50% to 55% gravimetric water). Also, the shape of aggregated was orthogonal. At higher soil salinity levels, the mean width and depth of cracks increased. At the end of the experiment, average width and depth of 5 dSm-1treatment were 4.9 and 16.6 cm, respectively, . In desiccation period, the trend of crack index changes showed that 2 dSm-1treatment had the lowest crack development and this factor increased by increasing soil salinity.

Study on release rate of nonexchangeable potassium (NEK) is necessary for management and optimum use of soil resources and determination of availability and supplying power of potassium in soils containing potassium minerals. Information about NEK release rate in Fars Province calcareous soils is limited. The objective of this study included an investigation of the dynamics of NEK in some soils from Fars Province by successive extraction with 0.01M Oxalic acid and determination of the relation between kinetics of NEK release with soil properties and clay mineralogy. The results of this experiment showed that the initial NEK release rate was rapid, but slowed down later on. Results showed that cumulative K release ranged from 91 to 233 mg kg-1(average 144.3 mg kg-1). The amount of NEK released after 1028 h was significantly correlated with CEC, NEK, and CCE. Elovich, power function and First order equations described well the NEK release kinetics based on their highest determination coefficient and their lowest value of the standard error of the estimate. Maximum of potassium release was observed in Vertisols, probably because of high amount of clay content and the clay mineral of smectite and mica. Also, the amount of K release was in the following order: Vertisols>Alfisols> Inceptisols> Entisols>Aridisols. In the correlation test, the rate constants in the kinetic equations were correlated with some chemical properties and particle size distribution.

In this study, spatial variability of infiltration rate was investigated on a landscape of 6.1 percent slope in Kuhin region. Infiltration rate was measured by double-rings infiltrometer at 33 points of 50-meter intervals along the landscape. Composite soil samples (0-15 cm) were collected during the infiltration experiments. The soil samples were analyzed for bulk density, aggregate stability, initial soil moisture content, textural fractions, organic matter and calcium carbonate equivalent. To investigate the spatial variability and fitting the best model, geostatistical methods were used by variogram analysis. Most of the measured properties showed spatial dependence. The content of calcium carbonate equivalent showed the strongest spatial dependence by 0.17 percent nugget effect. Final infiltration rate and parameter A of Philip's equation showed strong spatial dependence, coefficient a of Kostiakov's equation showed moderate spatial dependence, and S parameter of Philip's equation and b coefficient of Kostiakov's equation showed pure nugget effect.

Development of residential, commercial, and industrial areas and agricultural land use in sSouth of Tehran has, have caused changes in some physical and chemical properties in the soil environment. In this research, 196 soil samples were collected at depth of 0-30 cm, at 1000×1000m grids in 20000 ha agricultural lands of Ssouthern of Tehran. Soil texture, pH, calcium carbonate, cation exchange capacity, and organic carbon were measured. Geostatical analysis and, interpolation of soil properties by kriging and mapping were carried out by GS and ArcGIS software. Results showed that 26.3% and, 54.6% of lands were containeding of less than 0.9% and 0.9- to 1.2% of organic carbon, respectively. A lLands containing less than 0.9% of organic carbon is are often cultivated crops, residential areas, and barren lands. The land containings of 0.9-2.2% organic carbon is often cultivated to vegetables crops. Except the 29.9% of which lands which were affected by industrial waste water with a pH greater than 8, the remaining of lands have had a pH of 7.5 to 8. About 81% of the lands have had 5% to 15% lime and 78.6% of the lands have had a CEC of 20-35 cmolc kg-1. In this study, spherical models were fitted for organic carbon, pH, CEC, and lime. Exponential models were fitted for clay and silt and Gaussian model for sand. Use ofing wastewater, intensive agriculture, and specific management, especially for cultivation of vegetable crops, were had significant effects on soil properties.

Among various destruction factors affecting forests and grasslands, especially in arid and semi-arid regions, fire is considered the more dangerous factor and results in different physical, chemical, and biological changes in soil properties depending on the conditions. This study aimed to evaluate the residual effects of previously burned pastures on some soil chemical properties in Fereydan region of central Zagros. Fire in these areas was mainly due to human impacts. The experiment was conducted in a completely randomized design with unequal replicates. Calcium carbonate equivalent and organic matter contents, soluble sodium, potassium, calcium and magnesium, available phosphorus, iron, manganese and zinc were measured by standard methods. The results showed that fire had a significant effect on some of the measured soil chemical properties. Soil organic matter content, soluble potassium, calcium and magnesium, available phosphorus, iron and manganese were increased due to firing. Mean comparisons showed that soil organic matter increased from 2.10% in the unburned to 4.12% in the burned portion of pasture. The soluble potassium, calcium and magnesium increased from 0.45, 6.42, and 1.19 in the unburned to 0.95, 9.91, and 2.22 meq/l in the burned areas, respectively. The available phosphorus, iron, and manganese were increased from 31.30, 18.22, and 37.29 mg/kg in the unburned to 34.17, 20.39, and 55.64 mg/kg soil in the burned soil. The overall impact of burning on soil chemical properties was greater in the first year after the fire, and the effect decreased with time.