نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و نهم شماره 4 (زمستان 1394)

In Iran, most of the soils have high lime with low organic matter content. Therefore, boron deficiency is very probable in the soils. In order to determine the best level and method of boron application in common bean farms, a 3-year field experiment was conducted as a complete randomized blocks design with ten treatments and three replications in Eghlid Agricultural Research Station. The highest grain yield (2472 kg.ha-1) was obtained from foliar application with 0.1% boric acid at two times: one and two months after shooting. This treatment had no significant difference with 0.025% of boron foliar application treatment. In fertigation method, the highest grain yield (2319 kg.ha-1) was obtained by application of 4 kg.ha-1 boric acid. According to the results, foliar application of boric acid at a concentration of 0.025% or soil application of 4 kg.ha-1 as fertigation in the same conditions is recommended.

Alternate bearing is a common phenomenon in most commercial perennial fruit trees and negatively impacts the net returns to producers. Alternate bearing is the most important problem in “Siaho” mandarin production. In order to alleviate this problem, treatments including different times of nitrogen foliar application and harvest time were investigated for five years on 36 bearing Siaho mandarin trees in Haji Abad, Hormozgan province. Results showed that yield fluctuations were more in early years of the experiment than later years. Reduction in alternate bearing was observed with nitrogen spraying in November: foliar nitrogen with 0.5 % urea in November reduced alternate bearing index (range: 0-1) significantly compared to one and two months later. Alternate bearing index value for November was half (0.062 compared with 0.113) and about one-third (0.062 compared with 0.160) in comparison with January and February spraying time, respectively. Harvest time had no significant effect on alternate bearing index. In order to alleviate alternate bearing in “Siaho” mandarin, November is the best time of nitrogen foliar application.

In order to investigate the effect of plant growth promoting rhizobacteria on yield and dry matter remobilization of spring barley at different levels of nitrogen and phosphorus fertilizers, an experiment was conducted in two years at the Research Farm of Islamic Azad University, Ardabil branch, during 2009-2010 and 2010-2011 crop seasons. The combination of nitrogen fertilizer at three levels (0, 40 and 80 kg N/ha as urea) and phosphorus fertilizer (0, 30 and 60 kg P2O5/ha) were factorially assigned to the main plots and seed inoculation with plant growth promoting rhizobacteria at four levels (no inoculation, seed inoculation with Azotobacter chorchorum strain 5, Azosprilium lipoferum strain OF and combination of Azotobacter Azosprilium) were assigned to the subplots. The results showed that with increase in N and P rates and seed inoculation with plant growth promoting rhrizobacteria, total remobilization of dry matter from plant and from stem and their contribution to grain filling decreased. The highest dry matter remobilization and contribution to grain yield were observed at the control levels of the experimental factors. The maximum grain yield, 1000 grain weight, number of grains per ear, number of tillers per plant, biological yield and harvest index were obtained in the plots which had received the highest rates of N and P fertilizers and seed inoculation with both Azosprilium and Azotobacter. The minimum of these parameters were obtained in plots without application of experimental factors. Based on the results, it was concluded that application of the highest rate of nitrogen and phosphorus (80 kg N.ha-1 and 60 kg P.ha-1) in seed inoculation with Azospirillum and Azotobacter can be recommended for profitable barley production in the study area.

Understanding the factors affecting water and solute movement in the soil profile and the use of new amendments like biochar can help the proper management to reduce nitrate leaching from the root zone and prevent the pollution of underground waters. This research was conducted to study the effect of rice husk biochar of two sizes (natural and finer than 1 mm) in two application rates (1% and 3%) in the presence and absence of compost (1 %) on nitrate leaching in a clayey soil during a five months period. The experiment was based on completely randomized design with three replications. The biochar was produced from rice husk under pyrolysis condition at 500 °C under limited oxygen condition. The pots were subjected to wetting (field capacity plus 20 percent) and drying (permanent wilting point) cycles, and nitrate concentration was measured monthly in the bottom outflow. The highest and least rates of nitrate leaching were observed in the treatment that contained compost-without biochar and the treatment containing biochar without compost, respectively. Biochar addition to the soil at both rates and both sizes significantly reduced nitrate leaching compared to the control during the whole time. In overall, nitrate leaching was higher in the treatments containing compost compared to those without compost. The particle size of biochar had no effect on its efficiency of nitrate leaching. Nitrate leaching showed a drastic reducing trend during the first three months and had an increasing trend in the last two months.

Limited information is available about the ability of clay minerals such as sepiolite and palygorskite to reduce bioavailability of Pb and Cd for plants. A pot experiment was conducted using a randomized complete block design to assess and compare the ability of Iranian sepiolite (Yazd) and Spanish palygorskite (Tolsa Co.) on biomass production and uptake of Pb and Cd from a contaminated soil by spinach. A soil sample (0-30 cm depth) was taken from research farms of Shahid Chamran University of Ahvaz and artificially contaminated with Pb and Cd solutions (150 mg/l). Treatments included polluted soils with no amendments (control), with 20 g kg-1 sepiolite, and with 20 g kg-1 palygorskite. Six seeds of spinach (Virofly cultivar) were then planted into each pot and loss of water was replenished daily using distilled water to reach field capacity throughout the experiment. After 45 days, the plants were harvested and the concentrations of Pb and Cd in roots and shoots were determined using atomic absorption spectroscopy. The results showed that application of both sepiolite and palygorskite significantly increased root and shoot dry biomass compared with the control. However, after application of both sepiolite and palygorskite, bioaccumulation factor (BF) of Cd and Pb in roots of spinach decreased by 78.1% and, 56.2% and in shoots by 91.7% and 75%, respectively. Both sepiolite and palygorskite minerals showed more tendency to adsorb Pb than Cd. The results demonstrate that both sepiolite and palygorskite could be effective in reducing Pb and Cd bioavalability and accumulation in spinach. However, sepiolite was more effective than palygorskite.

Sorption is one of the most important chemical processes which affect zinc (Zn) behavior in the soil. In this study, the effects of soil properties on Zn adsorption were studied in 25 soil samples from the North-West of Iran in batch system as a function of initial Zn concentration (0-0.49 mM). Results indicated that cation exchange capacity (CEC), calcium carbonate equivalent (CCE), and soil pH were primarily responsible for retaining of Zn in all the soil samples. Eighty percent variability in the adsorption maxima (гmax) of Zn was attributed to silt, CEC, and soil pH. CEC positively influenced гmax of Zn, while the reduction of pH and silt content of the soils increased гmax capacity of Zn. Langmuir equation (R2=0.99; RMSE=0.22) proved more effective in describing Zn adsorption in soils as compared with Freundlich isotherm (R2=0.93; RMSE=0.59). The гmax of Zn in these 25 soils ranged from 2.62 to 15.56 mmol kg-1. Langmuir 2-surface isotherm showed that the Zn binding strength in the high energy surface (K1L) was about 4.2 times greater than on the low-energy surface (K2L) while гmax of Zn in the low energy surface was about 1.6 times greater than on the high energy surface of adsorption sites of soils. Regression model as a function of soil Langmuir equation parameters and soil physicochemical properties to predict Zn availability demonstrated the utility of Langmuir parameters.

The objective of this study was to compare the environmentally friendly mulches for sand dune stabilization in a laboratory study. Based on the literature review, some of the materials used as sand stabilizer in recent years were selected in this study. The trays of sand samples treated with mulch were air-dried for several days after mulching in a factorial experiment with a completely random design. The treatments were mulch types including organic mulch (M1, M2), clay mulch (M3, M4), inorganic mulch (M5), polymeric mulch (M6, M7, M8) and the thickness of mulch (1 or 2 layers). Surface soil shear strength (SSS), penetration resistance (PR) and shear resistances of the selected mulches were measured by shear vane, penetrometer, and Zhang’s shear device, respectively. The results indicated that M5 had the highest PR value and the average value of PR for M5 treatment was 1.16, 1.27, 1.32, 1.28, 1.14, 1.14, and 1.05 times greater than those obtained for M1, M2, M3, M4, M6, M7, and M8 treatments, respectively. The average value of SSS in dry condition for M6, M7, and M8 treatments was, respectively, 1.61, 1.29, and 1.11 times greater than those measured in saturation condition. Also, M6 had the highest adhesion parameter of surface shear resistance (SSR) value. The average value of adhesion for M6 treatment was 13.46, 7.93, 2.41, 2.35, 3.40, 2.85, and 1.37 times greater than those obtained for M1, M2, M3, M4, M5, M7, and M8 treatments, respectively. It is concluded that, in laboratory conditions, mulch 5 (2500 gr calcium and magnesium chloride 1000 ml water) was a superior mulch for Ahvaz sand dune stabilization because of suitable SSS and PR rate and its ease of spraying on sand surface.

Water repellency (WR) of various degrees reported for different soil textures, land use, and climate conditions may decrease infiltration and increase runoff and soil erosion. WR can be influenced by soil amendments and may vary over time. In the present study, a completely randomized design experiment with three replications was conducted to evaluate the effect of soil amendments on dynamic and static WR in a calcareous soil. Treatments consisted of two organic (polyvinyl acetate, PVA and polyacrylamide, PAM at 4 levels of 0, 0.05, 0.1 and 0.2 g kg-1 soil) and two mineral amendments (pumice and perlite at 4 levels of 0, 0.5, 1 and 2 g kg-1 soil). Dynamic (water drop penetration time) and static WR(equilibrium contact angle of soil and water) of the studied soil samples were measured at three time periods of 10, 30, and 60 days after amendments application. Application of PAM, pumice, and perlite decreased dynamic and static WR significantly, whereas PVA increased it. Dynamic WR increased over time, but not significantly in PAM, pumice, and perlite treated soils. Dynamic WR increased by 40% after 60 days as compared to 10 days after PVA application. In pumice treated soil, the static WR did not vary significantly over time. Polyacrylamide and PVA increased static soil WR by 4% and 2%, respectively, at 60 days as compared to 10 days after applications. Results indicated that PAM, pumice, and perlite as soil amendments can reduce soil WR and, as a consequence, increase water retention in soil. In overall, the influence of perlite in decreasing dynamic soil WR was greater than the other amendments.

Agh Emam(2) Watershed is one of the watersheds in the Golestan Province with an area of 2595 hectares and has considerable problems with soil erosion, particularly gully erosion. In order to carry out this study, at first, the total number of linear gullies in the study area (eleven gullies) was determined. Then, different physical soil properties (sand, clay, silt, and moisture saturation percentage) and chemical soil properties (electrical conductivity, bio- carbon, lime, cation exchange capacity, sodium adsorption ratio, and exchangeable sodium percentage) were investigated by soil sampling (eleven samples) inside the gullies and in the watershed upstream of the gullies at two depths (0-20 centimeters and 20-50 cm). Non- soil effective factors in development of linear gullies including slope classes, altitude classes, land use, and lithology were also evaluated. The results showed that, among soil characteristics, clay percentage (surface), silt percentage (surface), saturated moisture percentage (sub- surface), electrical conductivity (sub- surface), bio- carbon (surface and subsurface), lime (surface and sub- surface) and also lithology from non- soil factors had significant role in development of linear gully erosion in the study area.

Water repellency is a soil property with short-term (or seasonal) variations and reduces or even prevents water infiltration into the soil. When soils are dry, water repellency is found to be at its most extreme. The objective of this study was to investigate variations of soil water repellencyand determine critical soil water contents in 10 forestry sites covered by different plant species (Pinus taeda, Alnus subcordata, Pterocarya fraxinifolia, Sambucus ebulus, Boxus sempervirens, Parotia persica, Quercus castanefolia, Fagus orientalis, Acer sp. and sparse grass) in Guilan province. The soils were sampled two times at autumn and summer from 0-5 cm depth. The water drop penetration time (WDPT) test was used to measure the actual water repellency at the selected sites under the natural field-moist conditions. The potential water repellency was measured in undisturbed samples dried at 25 °C taken from the same sites. Actual water repellency was determined only at forest sites in summer. A wide range of soil water repellency classes (hydrophilic to extremely water-repellent soils) were detected at the examined sites. The results show that water repellency is the largest at the sites with sandy texture. In this research, positive correlations between logWDPT and organic matter content(r=0.42) and sand percentage (r=0.27) were obtained. Correlations between Log WDPT and clay percentage was negative (r= -0.35) and no correlation was found between pH and Log WDPT. The soil water content zone at which soils became water repellent (critical water content) was different for each site and it was a function of the soil properties. Critical water content was assessed in sandy soils (0-5 -cm depth) and ranged from 4.0-6.7 %, in silty­ clay­ loam and silty­loam, between 10.1-15.8%, and in silty ­loam and clay loam with high organic matter varied from 13.3-21.3%. Apparently, soil organic matter and texture influence the critical water content.