نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و نهم شماره 2 (تابستان 1394)

Iron is one of the essential micronutrients for plants. Despite sufficiency of total iron in soil، there is Fe deficiency in most soils. Changing of soil chemical properties is one of the effective manners to improve the Fe nutrition in plants. To investigate the effects of alfalfa green manure and mixed culture of maize and canola on some chemical properties of rhizosphere and bioavailability and uptake of iron، a greenhouse experiment was conducted using rhizobox systems in a factorial design، with 3 replications، two levels of green manure (0 and 2% w/w) and 4 cropping treatments (maize alone، canola alone، mixed maize and canola، and control). Results showed that the green manure addition reduced pH but increased dissolved organic carbon concentration (DOC) and soil organic matter (SOM) and thereby increased bioavailability of iron by more than 4 mg/kg of soil. Green manure addition also enhanced shoot dry weight and increased uptake of iron in canola shoot by 54 µg/kg soil. Results of simple correlation coefficient showed a dynamic relationship between increase in iron bioavailability in the rhizosphere and pH reduction and increase in DOC، SOM، and EC. The results of plant analysisshowed that green manure addition reduced concentration of iron in shoot of the mixed culture. Intercropping of maize and canola increased plant dry weight 4. 4 g per pot more than canola and 5. 5 g per pot more than maize in single culture. Therefore، green manure addition and mixed culture system were useful in increasing yield. Also، intercropping of maize and canola was effective in increasing iron in maize shoot.

Sulfur is the most important acidifying material which، due to having relatively low-cost، is commonly used for lowering soil pH and improving the availability of some soil nutrients in many regions of the world. The efficiency of sulfur application depends on many factors، such as the ability of calcareous soil to neutralize the acid resulting from sulfur oxidation. Therefore، determining the best rate of S-application to calcareous soils with different buffering capacity has an especial importance. With regard to sulfur utilization in order to increase nutrients availability in calcareous and alkali soils، few researches have been done about the rate of sulfur application and its relationship with soil calcium carbonate content. Hence، this investigation studied the effect of sulfur rates with Thiobacillus inoculant on soybean growth and uptake of some nutrients in 4 calcareous soils with different buffering capacity. To this end، a completely randomized factorial experiment was conducted using three replications، seven levels of sulfur applications (the rates to neutralize 0، 3. 1%، 6. 25%، 12. 5%، 25%، 50%، and 100 percent of soil calcium carbonate content) and four different calcareous soils (soils with 8%، 14%، 22%، and 38 percent of calcium carbonate). The analysis of data by SAS software showed that application of sulfur at the rates needed to neutralize 50 percent of calcium carbonate in soils، significantly increased the uptake of nutrients. But، further application of sulfur، decreased growth parameters and nutrient uptake by plants.

This study was carried out in rhizobox، with the aim of evaluating the effects of sorghum rhizosphere on changes in available zinc using 4 single-extractants. Two soil samples with relatively similar physical and chemical properties were used from two areas، one from a non-polluted area and the other from the vicinity of the zinc and lead concentrate factory. In both soil samples، zinc contents were raised to three levels (250، 375، and 500 mg kg-1soil) according to their initial Zn content. Inside space of the rhizoboxes were sectioned into 3 separate compartments using nylon filters (40 mesh) including S1 (rhizosphere area)، S2 (the adjacent area influenced by plant roots)، and S3 (away from the rhizosphere) and sorghum seeds were planted in the S1 area. The effects of plant root activity on zinc bioavailable forms including distilled water extractable، calcium nitrate، and DTPA were significant. The amount of zinc in the forms of DTPA extractable، calcium nitrate and distilled water extractable in the rhizosphere (S1) of non-polluted soil was more than the bulk soil by 8. 6%، 100%، and 130%، respectively، at three weeks. Although HNO3 extractable zinc in this zone was not different than bulk soil، it decreased significantly about 10% in the seventh week. This shows the influence of sorghum root activity on less bioavailable [S1] form of zinc at longer time interval (seven vs. three weeks). Increase of the bioavailability (p<0. 01) in the third week resulted in significantly more absorption (30%) by the plant in non-polluted soil. The results showed that plant concentration and uptake of zinc by sorghum had significant correlation with nitric acid extractable zinc in rhizosphere soil)p<0. 01). Therefore، the nitric acid method can be used as an appropriate assessment method of bioavailable zinc for sorghum with regard to increasing levels in soil.

The objectives of this study were to determine and compare the factors that influence cone penetration resistance (PR) under three land use types: virgin، under field crops، and sugarcane cultivated lands of Haft-Tapeh Agro-Industry، in Khozestan province. Accordingly، 80 soil samples from 0-40 and 40-80 cm were collected from each land use to establish regression equations predicting PR. Further، the possibility of using the slope of water retention curve at its inflection point (S index) to derive regression equations was investigated. In order to eliminate the effects of moisture content on the PR، measurements ​​were made at matric tension of 33 kPa. The results showed that variations of the factors affecting PR in virgin lands were more than those of sugarcane and arableones. In sugarcane and arable lands، PR values increased logarithmically with decrease in organic matter and mean weight diameter. Besides، S index was increased by reclamation of the virgin lands due to lowering of salinity and sodium-induced restrictions and improvement in organic matter content. Also، the results showed that at very low values of S index، PR depended on the compression forces and little change would occur with more reduction in organic matter content and mean weight diameter.

Accuracy of the pedo-transfer functions can be improved using more flexible equations. The objective of this study was to compare pedo-transfer functions with different flexibility [e. g. multiple linear regression (MLR)، the physic-empirical model of Arya and Paris (AP)، artificial neural network (ANN)، and group method of data handling (GMDH)] for predicting soil water contents at field capacity and permanent wilting point. Pedo-transfer functions were developed from data of particle size distribution، organic carbon، bulk density، and water contents at 0،. 33 and 1500 kPa. The accuracy and reliability of the GMDH algorithm was superior to the other pedo-transfer functions for predicting the soil volumetric water contents at field capacity and permanent wilting point، because of fewer lower roots mean squared error (RMSE) and AIC criteria and more larger agreement index (D-index). It seems that the GMDH preference superiority is due to its higher GMDH capability to determine nonlinear and complex relationships between soil factors affecting factors the soil water contents at field capacity and permanent wilting points.

Effect of compaction on soil chemical and biological properties was studied using a factorial experiment with completely randomized design and three replications. Treatments included soil compaction at three levels (normal bulk density، and 10% and 20 percent higher bulk density by compaction)، two types of soil (light and heavy texture)، and two measuring times (one week after wheat planting and after plant harvest). Chemical properties including pH، total nitrogen، and organic matter، and biological properties of respiratory and urease enzyme activity were measured. Results showed that the amount of respiration and urease enzyme activity in natural densities، with an average of، respectively، 47. 18 µg CO2 and 65. 08 µg NH4 per gram of soil، had the maximum values. Also، normal compaction with a mean of 0. 131 percent nitrogen content had the maximum. The results indicated that by increasing soil compaction، index of soil mechanical resistance would increase and، by changing pH، the soil microbial activity would change in the way that soil respiration and enzyme urease activities would decrease. Consequently، the amount of soil nitrogen will decrease.

Soil temperature regime has a direct effect on plant growth، biodiversity، and soil biological activity. However، available soil temperature data are insufficient، while their reconstruction for agro-climatic and ecological studies is important. Soil temperature at different depths has different spatial and temporal behavior. In this study، we tried to predict monthly data using the time series of soil temperature at depths of 5، 20، and 30 cm in Hamadan Airport Station for the period 1996 to 2008. The results showed that soil temperature followed seasonal SARIMA model. The best time-series structure for 5، 20، and 30 cm depths were SARIMA (2،0،0) (2،0،0)، SARIMA (1،0،0) (1،0،0) and SARIMA (1،1،0) (1،1،1)، respectively. The calculated R2 and RMSE for the selected depths were 0. 96 and 1. 63 ºC for 5 cm depth، 0. 98 and 1. 49 ºC for 20 cm depth، and 0. 97 and 1. 56 ºC for 30 cm depth. Considering the suitability of the estimated results، the model was used for prediction of the soil temperature for 2009-13، which revealed negligible variation in soil temperature trend during this period.

The aim of this research was to study dynamics of soil CO2، CH4 and N2O fluxes related to variability of some soil characteristics in different ages of pit and mounds i. e. the microtopography created by uprooted trees. For this purpose، the control parcel of Lalis district located in Mazandaran province was studied and twenty four uprooted trees from beech species were found. Pit and mound age was considered equal to the dead tree age. Based on this assumption، six، seven، five، and six dead trees belonged to young، medium، adult، and old pit and mounds، respectively. Soil samples were taken at 0-15 cm depth from top of the mound، pit bottom، and closed canopy micro sites. Some of soil physico-chemical and biological characteristics (texture، water content، organic carbon، total nitrogen، abundance and biomass of earthworms) were measured at the laboratory. Results indicated that pits (0. 55 mg CO2، 0. 10 mg N2O and -0. 32 mg CH4 m-2 day-1) emitted more CO2 and N2O and had less uptake of CH4 compared to mounds (0. 19 mg CO2، - 0. 03 mg N2O and -0. 52 mg CH4 m-2 day-1). Potential of CO2 and N2O emissions and CH4 uptake are increased by pit and mounds with time. The results of this research can be considered in evaluation and management of forest ecosystems blown down by wind.

Land use changes such as conversion of forest to cultivated land significantly influence soil properties and modify soil forming processes. In order to study the effects of different land use on soil physical، chemical and biological properties، five sites of mountain landforms consisting of Bijarbagh (granite parent rock)، Zemeidan (basaltic andesite parent rock)، Alisorod (phyllite parent rock)، Khorma (basaltic andesite parent rock)، and Leil (andesitic basalt parent rock)، located in part of Lahijan and Langaroud regions were selected. Each site had forest cover and tea garden next to it. A representative profile in each land use was dug and three locations around the profile were selected for soil sampling (0-30 cm). This study was conducted in a factorial arrangement and completely randomized block design (CRBD). Results indicated that land use changes and parent material had significant effect on soil physical، chemical، and biological properties. Land use changes (forest to tea garden) significantly increased clay، silt، bulk density، and free iron oxides (Fed) with mean values of 12%،10. 5%،17%، and 5. 5 percent، respectively، but significantly decreased sand، pH، organic carbon (OC)، exchangeable Ca+Mg، exchangeable K، CEC، amorphous iron oxides (Feo)، biomass respiration contents and bacterial population with mean values of 3. 7%، 11%، 17. 7%، 29. 9%، 32. 6%، 18. 3%، 24%، 34%، and 22 percent، respectively.

This study compared the effects of exotic species، Taxodium distichum، with two native species، Populus caspica and Alnus glutinosa، on soil chemical properties in the Safrabasteh forestlands of Astaneh Ashrafieh region. A factorial experiment was conducted in the framework of completely randomized block design with two factors: (1) three types of tree cover and (2) two levels of sampling depth، with three replications. For each replicate، plots of 100 m2 were chosen and soil samples were taken at the center and every four corner of the plots in each depth. Then، samples of each depth were mixed and one combined sample was used for chemical analysis. Some soil properties such as pH، electrical conductivity، organic carbon، total nitrogen، humic and fulvic acid، equivalent calcium carbonate and C/N ratio were determined. The results revealed no significant difference in pH of soils under three forest cover، however، there were significant differences in the other parameters. Decrease in soil electrical conductivity was due to alluvial parent material، high rainfall in this region، and proximity to the Sefidrood River، which caused more leaching in the soil. Taxodium distichum led to increase organic carbon، nitrogen، humic and fulvic acid in soil in comparison with the two native forest covers، Alnus and populous. However، differences among interaction of forest species with soil properties observed in both depths could be due to the different qualities and quantity of litter، bush and proceses that occur in the forest floor. It also depends on root function and elemental recycling. Furthermore، C/N ratio was the lowest in soil under Alnus glutinosa cover، which is probably related to higher biological activity and nitrogen fixation. It can be concluded that Taxodium distichum has had secondary effects on the soil during the last three decades. Thus، further and more detailed studies are necessary in the future; or by using biological and biochemical indexes that give faster response to the environmental changes، the effect of various species on soil quality could be studied.