نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و هشتم شماره 4 (زمستان 1393)

In order to investigate the possibility of planting grass pea and common vetch crops after harvesting wheat and to evaluate the effects of green manure of these crops on yield of potato-wheat in croprotation cycle، this research was carried out using a Randomized Complete Block Design with four replications during 2006-2010 at Khair-Abad Research Station، Zanjan، Iran. The treatments were either removal or addition of grass pea and common vetch green manure as well as of wheat green manure (originating from threshing grains as the control) into the soil. Analysis of the data obtained from two cycles of crop rotation revealed significant difference (at 1% level) among the treatments in terms of forage dry matter yield and nitrogen accumulation in tissues of the above ground organs. The lowest amount of dry matter (1. 63-1. 95 t/ha) and nitrogen accumulation (17. 67-21. 22 kg/ha) was recorded in the control. Between grass pea and common vetch، there was no significant difference in terms of forage dry matter yield. In combined analysis of the results، the effect of treatments on mean yield of potato and biological and grain yield of wheat was significant. The highest amounts of this characteristic were obtained from addition of grass pea and common vetch green manure. In the treatment consisting of addition of common vetch green manure، the mean yields of potato (38. 47 t/ha) and wheat (3. 71 t/ha)، mean weight diameter of soil particles (1. 46)، and soil organic carbon (0. 77 percent) were higher than the other treatments. Results of this research show the successful effects of planting grass pea and common vetch in summer fallow condition along with positive effect of green manure addition of these crops on the performance of potato and wheat and some soil characteristics.

Walnut tree is grown for multiple purposes. Indeed، it is economically important and increasing its yield and improving its quality in order to compete in the international markets is one of great importance. To this end، one significant management practice is proper use of suitable fertilizers. Zinc and Phosphorus are two important elements in the nutrition of walnut. In this study، experiments were conducted with 3 phosphorus levels (0، 150، and 300 kg P2O5. ha-1) and 3 zinc levels (0، 15، and 30 kg Zn. ha-1) by using factorial arrangement in randomized complete blockdesign with four replications. Addition of phosphorus significantly affected concentration of P and Fe in the leaves. Phosphorus application of 150 kg. ha-1significantly increased copper concentration in the leaves. But، the application of higher levels of phosphorus decreased it. Also، Zn application increased its concentration in the leaves، but significantly decreased concentration of P in the leaves. The results of the study showed P application of 150 kg. ha-1significantly increased the dried weight of nutmeat، but application of higher levels of phosphorus decreased it.

Salinity is one of the major environmental stresses that adversely affects plant growth and metabolism. Salt stress affects plant physiology at both whole-plant and cellular levels through osmotic and ionic stress effects. In Iran، orchard crops such as almond are mainly confined to irrigated fields. Irrigated agricultural lands in arid regions، characterized by chronic drought، extreme temperatures، and scarce precipitation، induce accumulation of salt in soils following a combination of sustained evaporative and transpirational water losses. In order to evaluate of physio-biochemical response in almond trees to salinity stress، the present investigation was carried out. One-year old almond seedlings (Mamaei cultivar) were subjected to different salinity treatments: 3، 5، 7، and 10 dS. m-1). Characteristics of photosynthetic pigments (involving، Chl. a، Chl. b، Chl. (a + b) and CIS)، concentration of nutrient elements and some biochemical parameters were measured. Our study revealed a strong and negative relationship between increasing salinity intensity and most of the measured parameters related to photosynthetic pigments. Our results showed a competitive process among the measured nutrients ions (amongst Na+، Cl-، and K+، Ca2+) and soil salt content. In conclusion، the photosynthetic pigment traits، nutrient element contents، and biochemical parameters measured under NaCl treatments indicate that almond seedlings studied can be regarded as salt sensitive.

Cadmium is a highly toxic heavy metal and one of the most important environmental pollutants. Cadmium has a particular interest among the heavy elements due to the high mobility، solubility، and toxicity for human، plants، and other organisms. In order to study cadmium toxic effect on green pepper، a completely randomized design was performed with three levels of cadmium (0، 0. 25، and 0. 5 mM as cadmium chloride) in three replications under greenhouse conditions. The result showed that cadmium had a negative effect on some morphological traits of green pepper. In this regard، concentration of 0. 5mM of cadmium caused significant decrease (p<0. 05) in root volume، root length، leaf number، fresh weight and dry weight of shoot and root by، respectively، 45. 8%، 12. 2%، 18. 5%، 38%، 15. 3%، and 20. 7 percent compared to the control. Also، results showed that increase in the levels of cadmium lowered the content of photosynthesis pigments: at the concentration of 0. 5mM، cadmium caused a significant reduction (p<0. 05) in chlorophyll a، b and total chlorophyll content at the rate of، respectively، 26. 5%، 34. 7%، and 18. 2 percent relative to the control. Besides، analysis of variance showed significant reduction in the relative water content of plant tissue as affected by cadmium toxicity: this index decreased 14. 5 percent compared to the control treatment. But، there was no significant difference between the two levels of cadmium treatment (p<0. 05). According to the results of the present study، cadmium caused reduction of growth، damage to the plant، and had negative effect on physiological processes of green pepper. In general، the toxicity of this element varies in different plant species and cultivars، therefore، more studies will be useful on different crop varieties.

Presence of arsenic، a heavy metal، in soil and water resources originating from geological formations of Qorveh plain، which is considered as the main agricultural zone of Kurdistan province in western Iran، has put the agricultural products of this region at risk of pollution. Since arsenate، as the most abundance form of arsenic in soil environment، competes against phosphate anion; application of ammonium phosphate fertilizer across farmlands in this region requires careful study. Hence، four soil columns were made using a polluted soil sample obtained from the region. In the study، two control columns and two test columns were under weekly leaching process by pure and ammonium phosphate fertilizer containing distilled water، respectively، for six months. The results showed that there was no significant difference between the control and the test columns regarding amount of arsenic leached (P>0. 05). After the six months of leaching; seven soil samples along every 10 cm of each soil column were taken and analyzed. According to the results، concentration of arsenic measured at the surface of the test columns was less than the control columns. Moreover، arsenic concentrations significantly differed at various depths of both the control and the test columns (P<0. 01). Therefore، it could be concluded that the phosphate supplied to the test columns replaced arsenic at the soil surface encouraging arsenic to move into deeper layers where more root activities of cultivated plants are expected.

Improvement of soil properties through sustainable agriculture requires suitable management of plant residues. This study was conducted to investigate the effect of different types and managements of plant residue on soil physical properties in a field experiment as factorial based on RCBD with three replicates. The first factor was residue type including barley straw and alfalfa residue، and the second was different managements including 1) incorporating one percent of the plant residues with the soil (MIX1)، 2) incorporating 0. 5 percent of the plant residues with the soil (MIX0. 5)، 3) surface retention­­ of plant­ residues (SUR)، 4)، burning plant residues (BUR) and 5) control (C). The results showed that the applied managements of plant residue had significant effects on the selected soil properties. In comparison to the control، MIX1 application of barley straw resulted in the highest increases in organic carbon content (70%)، total porosity (23%) and final infiltration rate (82%)، and the highest reduction in bulk density (40%). In contrast، burning the alfalfa residue led to the highest reductions in organic carbon (200%)، total porosity (29. 5%)، the final infiltration rate (30%)، and the highest increase in bulk density (5. 5%). In addition، MIX0. 5 and SUR treatments improved the soil properties significantly. The highest and the least infiltration rates were found in MIX1 of barley straw (48. 6 mm/h) and BUR of alfalfa residue (4. 6 mm/h)، respectively. Overall، with respect to the improvement of soil properties، the managements of plant residue were prioritized as: MIX1>MIX0. 5>SUR>C>BUR.

Soil particle-size distribution (PSD) is one of the most important physical attributes due to its great influence on soil physical، chemical، and biological properties. Water infiltration rate، land-use change، soil erosion، and biological soil crusts (BSCs) may influence PSD in a soil. The multifractal measures were useful tools in characterization of PSD in soils. The objective of the current study was to investigate the effect of BSCs on multifractal spectrum of soils. To this end، sixteen soil samples were collected from 0-5 cm and 5-15 cm depths in soils with and without BSCs in Qara Qir rangeland، north of Agh Ghala city of Golestan province، Iran. Particle size distribution was measured by the hydrometer method. Results showed that soils PSD had multifractal behavior. Multifractal spectra followed the typical sigmoidal shape. The result showed that fractal dimensions (i. e. D0. 5، D1، D1. 5، and D2) were significantly positively correlated with clay content and significantly negatively correlated with sand content. In the current study، the (D0 –D2) index was used for investigation of multifractality. The average largest D0 –D2 was obtained at 0-5 cm depth of soil with BSCs (0. 295) and average smallest D0 –D2 was obtained at 5-15 cm soil depth of soil without BSCs (0. 240). Results showed that PSD of soils with BSCs had higher multifractality compared to those of soils without BSCs.

The range of the soil volumetric water content at which plant growth is least limited in relation to water potential، aeration، and mechanical resistance is the least limiting water range (LLWR). Experimentally، measurement of LLWR is expensive and time consuming. Using pedotransfer functions (PTFs) can facilitate its prediction. There are، however، contradictory information about the accuracy and reliability of the developed PTFs for soil hydraulic properties using various methods including artificial neural networks (ANNs)، multi-objective group method of data handling (MGMDH) and multivariate linear regression (MLR). Evaluating the performance of these methods in direct prediction of LLWR was the main purpose of the present study. To this end، 188 undisturbed soil samples were used to determine water retention and soil resistance curves and finally four moisture coefficients (θpwp،θ fc،θ sr،θ afp) and disturbed samples for measurement of eleven various soil physical and chemical attributes. After calculation of LLWR from upper and lower limits (LLWRe)، another time it was directly predicted from soil attributes (LLWRd) using the three mentioned methods. Accuracy and reliability of the developed PTFs was evaluated using root mean square error (RMSE)، Akaike information criterion (AIC)، and relative improvement (R. i). ANNs appeared as the most accurate and reliable one for LLWRd prediction (lower RMSE and more negative AIC); MGMDH and MLR ranked in descending order. Significant differences between accuracy and reliability of the developed PTFs by the three methods was evaluated using AIC. Differences between developed PTFs by ANNs and MGMDH versus MLR method were statistically significant، but differences between ANNs and MGMDH were only significant for the training step. Among the three methods studied، ANNs had the highest performance in LLWRd prediction.

A major concern of farmers is deterioration of the soil and water resources. Soil management is the most direct way for mankind to interfere with natural processes that may either intensify or hinder soil degradation. Fractal geometry has been widely used to describe heterogeneity in a wide range of natural processes، including physical systems of soil. In this study، the effects of different management practices on soil physical properties have been studied using fractal geometry. Fourteen farms with different soil management practices were selected within Mereg watershed located in Kermanshah province. The management practices information were obtained from the field survey، and used to determine the conditions of the experimental farms. Different soil samples were taken from these farms to determine soil physical properties in the laboratory. Results showed that the fractal dimension of aggregates could reflect the impact of soil management practices on aggregate size distribution. Suitable management practices such as reduced tillage، proper rotation systems، and using manure improved the soil aggregation and reduced fractal dimensions. Intensive tillage، plowing the steep slopes، and improper management of crop residues، on the other hand، enhanced the breakdown of aggregates and increased fractal dimensions of aggregates. Agroforestry system was the best management practices in this area.

Boron (B) is an important plant essential micronutrient whose availability is influenced by many soil factors. Adsorption–desorption processes play a major role in governing the solubility of boron in soil solution and، consequently، its availability to growing plants. To assess the effect of sodium adsorption ratio (SAR) on availability of B، adsorption of B was investigated in a sampled calcareous soils that had low levels of electrical conductivity. Boron adsorption experiments were carried out on the soil in batch systems to determine adsorption isotherms (amount of B adsorbed as a function of equilibrium solution B concentrations). To determine the quantity of adsorbed B، 5 g of soil were shaken for 12 h، in propylene 50 mL tubes، with 20 mL of B solution (0، 2، 5، 8، 10، 15، 20 mg L-1) (as boric acid) at ionic strengths of 0. 12 M (prepared by NaC1، CaC12. 2H2O، MgCl2. 6H2O) at five SAR levels (2، 5، 10، 15، 20). The reaction temperature was 25◦C. The suspension was centrifuged، filtered، and a sample was removed and B was determined by Azomethine-H spectrophotometric method (at a wavelength of 420 nm). Soil B adsorption was calculated by subtracting B in the solution after filtration from the added boron. Langmuir، Freundlich، linear Freundlich isotherms fitted well to the adsorbed data based on R2 and SEE. However، the fit of the Langmuir equation was closer to the experimental data. At different SAR values، the soil exhibited different adsorption behaviors. The effect of SAR on the boron adsorption was greater at high concentrations and the highest adsorption was at SAR 15، except for SAR 20 that had the lowest B adsorption. Effect of sodium adsorption ratio on adsorption of boron may be due to the dissociation of boric acid to borate anion and changes in the thickness of the diffuse double layer.