نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و نهم شماره 1 (بهار 1394)

Most plants are able to increase soil phosphorus availability by exuding some compounds such as organic acids when they experience phosphorous deficiency. Considering this special ability of plants، the main purpose of the present research was to investigate if application of organic acids may increase P availability in soil. Therefore، a greenhouse experiment was conducted with five treatments of different combinations of mono-calcium phosphate and oxalic acid in a completely randomized design with three replications in a calcareous soil. Treatments were 68، 40. 8، 27. 2، 13. 6، and 0 mg kg-1 of phosphate fertilizer respectively combined with 1. 6، 2. 4، 3. 2 and 4 mmol kg-1 of oxalic acid in soil. Plants were harvested after two months. Then، shoot dry matter، P concentration and uptake of plant and soil P concentration were measured. The results showed that the range of oxalic acid concentration (1 to 4 mmol kg-1 of soil) was effective for increasing phosphorus availability in soil. Applying oxalic acid instead of P fertilizer not only did not reduce plant dry matter، but also led to a significant increase in P uptake of plant. Moreover، phosphorous uptake efficiency of plant was increased by adding the oxalic acid to the soil. The results also showed that the combination of 27. 2 mg kg-1 of calcium phosphate (as 40 percent reduction in phosphorus fertilizer requirements of plants) and 2. 4 mmol kg-1 of oxalic acid was the best combination of acid and fertilizer among the other treatments for increasing the availability of phosphorus.

Phosphorus is an essential element for plants. Much of the agricultural lands of Iran has calcareous soils، in which، due to high pH، phosphorous availability is less، therefore، it appears as a limiting factor for plant growth. Application of biofertilizers instead of chemical ones has gained attention in order to produce healthy crops، reduce pollution of soil and water resources by reducing chemical fertilizers application، and to reduce cost of production. This research was carried out to evaluate the effect of biofertilizers on yield and quality of cucumber crop in field condition. The experiment was conducted as a factorial completely randomized block design with three replications at Dashti region of Esfahan province. Treatments were different rates of triple-super phosphate (100%، 75%، 50%، 25%، and 0% of phosphorous recommendation based on soil test) and inoculation (PGPR، phosphate solubilizing bacteria، un-inoculated control). Cucumber yield، root and shoot dry weight، chlorophyll index as well P، N، Fe، and Zn concentration of the shoot were measured. Results indicated that the effect of chemical and biofertilizers and also their interactive effects on all the measured parameters were significant (p<0. 05). In all biofertilizers treatments، increasing chemical fertilizer rates increased cucumber yield and P and N concentration in shoots. The highest P and N concentration in shoots belonged to phosphate solubilizing biofertilizer+ 75% of the recommended phosphorous rate، while the highest cucumber yield was related to PGPR biofertilizer+ 75% of the recommended P rate. Unlike P and N concentration، the concentration of Fe and Zn in cucumber shoots decreased by increasing chemical fertilizer rates. The highest and lowest concentration of Fe and Zn belonged to the control and phosphate solubilizing biofertilizer+ 100% of the recommended P rate، respectively.

Environmental problems associated with the excessive use of chemical fertilizers and abiotic stresses due to soil pollution by heavy metals have encouraged use of biological fertilizers in modern agriculture. In order to protect environment and reduce the tension caused by heavy metals، it is essential to use biofertilizer in crop production. To assess the effects of biofertilizers on yield and growth indices of tomato grown in cadmium contaminated soils، a factorial pot experiment was conducted using a completely randomized design with three replication. Factors investigated were levels of soil cadmium and the kinds of biological fertilizers used to inoculate tomato plant. The levels of soil cadmium were 0، 5، 10، 20، 40 and 80 mg Cd/kg soil and six combinations of biological fertilizers were used including: M0: without inoculation، M1: Phosphor solubilizing bacteria + plant growth promoting rhizobacteria + Azotobacter bacteria، M2: Azotobacter bacteria+ Mycorrhizal fungi + Azosperillium bacteria، M3: Plant growth promoting rhizobacteria + Azosperillium bacteria + Mycorrhizal fungi، M4: Mycorrhizal fungi + phosphor solubilizing bacteria + plant growth promoting rhizobacteria + Azotobacter bacteria، M5: Plant growth promoting rhizobacteria + Azotobacter bacteria + Mycorrhizal fungi. The results showed that application of biological fertilizers increased yield and growth indices when compared with the control، except fruit and stem diameter. The M2 combination increased tomato yield by 179. 8%، generating the highest yield of biological fertilizers that was significantly different from the other combinations. By contrast، the result of the combination of biological fertilizers M1 was not significantly different from the control.

Organic matter and its related soil properties are among the most important indicators of soil quality. Despite the importance of soil organic carbon، no comprehensive study has been done on organic carbon changes in soils of the Isfahan Province. The objective of this research was to investigate factors affecting soil organic carbon in soils of this province. A total of 248 surface soil samples were collected from different climatic zones of the province. Soil properties were measured by standard laboratory methods. Long-term temperature and precipitation data for 21 synoptic stations in the Isfahan Province were collected. Regression equation between each climatic parameter and elevation was established. These significant equations were used to estimate temperature and precipitation in the sampling points. Principal component analysis (PCA) was used to find the most effective factors which controlled soil variability in the study area. Multiple linear regression analysis was developed to estimate soil organic carbon in the study area. The results showed that four principal components control soil organic carbon in the study area، namely، climate and soil texture، soil salinity، gypsum، and calcium carbonate percentage. Climate and soil texture were identified by multiple linear regression as the most important factors influencing the soil organic carbon in the study area. There was significant statistical difference in the soil organic carbon percentage among different climatic zones. Due to considerable climatic differences and low amounts of soil organic carbon in the Isfahan Province، long-term planning and management practices are needed to prevent carbon loss and soil degradation، especially in arid and semi-arid regions.

Proper management of saline soils needs adequate information about the amount and salt distribution in the root zone. Irrigation is one of the factors that control the distribution of salt. This study investigated soil leaching simulation by using HYDRUS2D Software based on the evaporation of soil surface of a land without plant located at Shahid Chamran University، Ahwaz، Iran. Samples were taken from three distances of 0، 20، and 40 cm from the drip irrigation emitter and 0-20، 20-40، 40-60 and 60-80 cm depths. Among the measured depths، the 20 – 40 cm layer was revealed as the best working depths with a salt content of 5. 7 mg/cm3، while the depth of 60-80 cm had an average salinity of 10. 87 mg/cm3، the highest salt content compared with the other depths. Soil salinity decreased with time and irrigation. At the last irrigation، soil salinity under the dripper reached a salinity of 2. 13 mg/cm3 that was 1/15 of the initial amount. Salts movement in soil and leaching simulation by HYDRUS2D software showed that this software simulated salt distribution well.

For optimum planning، utilization، and management of lands، recognition of spatial variability of soil properties is necessary. This research was conducted to evaluate spatial variability of soil properties in 5000 ha of Arsenjan plain in Fars province. For this purpose، soil salinity، pH، particle size percentage، sodium، potassium، and organic carbon (OC) were measured on a systematic squared grid pattern with 500*500 m at 185 sites. For these variables، the best variogram model among linear، exponential، Gaussian، and spherical models with the highest R2 and the least error was determined using GS+، and ArcGIS software. The best interpolation method was also selected among kriging، co-kriging، and inverse distance weighted (IDW) methods for estimating data in non-sampled areas. To select desirable interpolation method، cross validation was used by statistical parameters of mean bias error، mean absolute error، mean square error، and root mean square error. The soil properties spatial variation maps were obtained with the best interpolation method. Results showed that soil properties had high variability. Soil salinity varied from 0. 44 to 11. 6 dS per meter، clay from 3. 4% to 42%، silt from 5. 8% to 93. 1%، and sand from 2. 4% to 79%. Soil texture had different classes at the study area، and there was significant correlation between soil properties. The best model for the single semi-variogram of soil salinity، pH، and clay percent was the exponential model; for silt and sand percent it was Gaussian model، and for OM the spherical model. In most cases، soil properties variogram models had small amount of nugget effect، high spatial correlation and high R2، and low amount of RSS. Although cross variogram parameters had acceptable amounts، soil variable kriging method was the unbiased estimator for most soil variables compared to co-kriging and IDW methods. The best interpolation method for silt percent was IDW، and for the other soil properties، kriging was the best one. Soil salinity and pH increased from north to south، especially toward south western. Clay percent، and OC decreased from west to east، and silt percent had the maximum amount in the center and east of the plain. Soil sodium and potassium had approximately similar trend، increasing from north to south and were affected by the low quality of irrigation water. This indicated that soil degradation and salinization has been occurring in the south part of the plain. Soil degradation and salinization is in progress and is a serious threat for the soil and water resource of this plain in the future.

Soil temperature is one of the most effective parameters for plant growth. Although the spatiotemporal monitoring of soil temperature is important for providing an optimum condition to maximize the yield efficiency، indirect measurements for zoning of soil temperature are essential due to difficulties in direct methods of measuring it and also the limited measurement points. Thus، the efficiency of some geostatistical methods including weighted moving average، kriging، and co-kriging with soil water content and electrical conductivity، as covariates، were investigated for estimating the soil temperature under three irrigation treatments: (FI) full irrigation، (PRD75) partial root zone drying at 75%، and (PRD55) at 55% levels. TDR sensors were used to measure soil temperature، water content، and electrical conductivity. Comparing the observed and estimated soil temperature by geostatistical methods based on root mean square error (RMSE)، mean absolute error (MAE)، mean bias error (MBE)، and index of agreement (d) indices confirmed the validity of the selected methods for zoning of soil temperature in the plant root zone under all treatments. Duncan variance analysis showed that the values of evaluation indices for kriging method were significantly lower than that for all other geostatistical methods under all treatments (P<0. 05). Results confirmed that using soil water content as covariate in co-kriging method significantly decreased the range of influence in all treatments and، also، using the soil electrical conductivity as covariate in co-kriging method caused a discontinuity of the cross-variogram. Thus، it could be concluded that even under the especial soil water content condition in partial root-zone drying strategy، kriging method significantly decreases the estimation error of soil temperature compared with co-kriging method with soil water content as covariate.

Hydraulic attributes play important role in hydrological studies، soil conservation، designing irrigation and drainage systems، soil conservation، and controlling soil erosion in watersheds. Their measurements are very tedious and time consuming and due to high spatial variability، a large number of measurements are required for obtaining reliable values. Nowadays، prediction of these attributes from the easily available soil properties has received increased attention. Therefore، the presentstudy aimed to introduce pedotransfer functions (PTFs) for estimation of some hydraulic coefficients in calcareous soils of Bajgah region in Fars province. In 100 sites، soils attributes including saturated and near saturated hydraulic conductivity، sorptivity coefficient، and hydraulic diffusivity were determined using Single Ring and Droplet methods and easily available soil properties including sand، silt، clay، bulk density، soil moisture، pH، calcium carbonate، gypsum، cation exchange capacity and sodium adsorption ratio were measured. Pedotransfer functions were derivate using stepwise multivariate regression method and were evaluated by calculating some statistical measures. In prediction of soil hydraulic attributes، easily available physical properties، i. e. sand content، geometric mean diameter of aggregate and soil particles، and saturated volumetric content as well as easily available chemical properties i. e. pH، organic matter، calcium carbonate equivalent، gypsum، total dissolved solids، cation exchange capacity and sodium adsorption ratio were entered in PTFs as estimator. The introduced PTFs could predict hydraulic soil attributes precisely with coefficient of determination of 0. 31 and 0. 92 and index of agreement of 0. 47 and 0. 97 for hydraulic diffusivity (the lowest accuracy) and sorptivity coefficient (the highest accuracy)، respectively. Due to tedious and time consuming nature of measurement of these attributes and the easy availability of the applied properties، the introduced PTFs can be used for prediction of these hydraulic attributes in the studied area as well as in other similar regions. Of course، to use these PTFs in other regions، the equations should first be locally tested and calibrated.

In order to better understand the extent of soil pollution by heavy metals and its effect on ecosystem، spatial information on ecological impacts of heavy metals would be necessary. Therefore، in the present study، the spatial pattern of ecological risk of heavy metals (cadmium، lead، copper، nickel and zinc) have been identified in surface soils of Golestan province. To this end، over 346 surface soil samples (0-30 cm) were collected all over the province. After the initial preparations، soil samples were digested using mixtures of different acids، and heavy metals concentrations were then detected. The accumulative risk of the elements were then determined for each sampling point on the basis of the background concentrations as well as available equations; then، the spatial pattern of ecological risks of the elements were identified using ordinary kriging technique. The results showed that the average total concentrations of cadmium، lead، copper، nickel and zinc in the study area، were 0. 12، 15. 42، 23. 9، 34. 88 and 82. 08 mg/kg، respectively، and the concentration levels (mg/kg) of Cd، Cu، Pb، Ni and Zn ranged from 0. 35 for cadmium to 37. 2، 84. 4، 75. 85 and 392. 4، for the other metals، respectively. Interpolation results also indicated that there were three main areas with very high ecological vulnerability in the province: a) a region in the center of the southern part of the province located in the mountainous area، b) a region where stretched as a tape from south to north in the east of the province، and c) a region in the northwest of the province، which covers the plain areas and Soofikam wetland and its adjacent regions.

Mapping based on total concentrations of micronutrients may be useful in fertility management including fertilizer and/or wastewater application. The aims of this work were to (1) investigate the spatial distribution of total concentrations of copper (Cu)، zinc (Zn)، manganese (Mn) and iron (Fe); (2) to select the suitable spatial estimator; and (3) to understand the effect of wastewater irrigation on the mapping of these elements in the Boroojen-Faradonbeh plain. To this end، 200 soil samples were randomly collected from surface soil (0-30 cm) of the Boroojen-Faradonbeh plain and some soil physicochemical properties as well as total concentrations of Cu، Zn، Mn، and Fe were determined. Total concentrations were below permissible limit of each element indicating no serious issue concerning pollution. Spatial distributions of Cu، Zn، Mn and Fe were best described by a spherical variogram model while that of Mn by an exponential one. Intermediate spatial dependence of all four elements indicated the greater influence of external factors compared with internal factors. Krigging (simple or ordinary) was a better spatial estimator compared to the inverse distance method (with exponents varying from 1 to 3). The maps revealed that concentrations، particularly those of Cu، Zn، and Mn، were higher in the eastern part of the plain where wastewater irrigation is practiced. Treated wastewater application seems to be the main factor elevating the concentrations in the eastern part of the plain.