نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و پنجم شماره 2 (تابستان 1390)

In order to study the effects of drought stress, zinc application and mycorrhiza inoculation on uptake of micro nutrients in maize (KSC 704), an experiment was carried out in research farm of Islamic Azad University of Arak, Iran, during 2006-2007. Experimental design was factorial based on RCBD with three replications. Treatments composed of irrigation levels at three levels (%100, %75 and %50 of crop water demand), mycorrhiza fungi at two levels (with and without inoculation), and Zinc sulfate at three levels (0, 25 and 45 kg ha-1). The results of combined variance analysis showed that drought stress significantly increased the concentration of copper, manganese, iron, and zinc, but reduced the concentration of boron. Inoculation with mycorrhiza fungi increased concentration of all nutritional elements. Using zinc sulfate increased the concentration of copper and zinc, but reduced the concentration of manganese, iron and boron. A negative antagonistic interaction was found between zinc and iron. Effect of water stress, mycorrhiza fungi, and zinc sulfate alone was significant on the percent of protein in grain at %1 probability level. Effect of interactions between irrigation and mycirrhiza fungi was significant on the concentration of copper and boron at %1 probability level, but it was not significant on the concentration of other elements. However, the concentration of all nutritional elements and grain percent of protein increased with mycorrhiza inoculation under drought stress. Use of zinc sulfate under drought stress increased the concentration of copper, manganese, iron, zinc and grain percent of protein, but reduced the concentration of boron. Interaction effects of mycirrhiza fungi and zinc sulfate increased the concentration of all nutritional elements. The highest zinc concentration and grain percent of protein was observed in the treatments consisting of inoculation with mycorrhiza fungi + 25 kg ha-1 zinc sulfate and irrigation at 50% and 75% water requirement, respectively.

Unsuitable agronomic management, such as intensive cropping and removal of whole crop residue from soils, has caused a gradual and continuous decline of soil organic matter in many arid and semi-arid regions. This mismanagement has resulted in improper soil physical properties. Application of organic wastes composts containing municipal solid waste and sewage sludge composts could solve the problem. Addition of composts to soil leads to the development and stability of soil structure. In order to study the effect of organic compounds on soil physical properties, this study was carried out with a completely randomized design in a factorial experiment in three replications. The treatments included soil type (silty loam and clay), type of compost (municipal solid waste, sewage sludge, and cow manure), and the amount of organic fertilizers (0, 75, 150, and 300 m3 / ha equivalent to 0, 175, 350, and 700 cm3/pot). Soil samples were air-dried, passed through 2 mm sieve, and mixed with composts treatments and filled in 7-liter pots. Physical properties of soil samples including bulk density, particle density, porosity, dispersible clay content and wet and dry mean weight diameter of aggregates (MWD) were measured. The highest decrease in soil bulk density and dispersible clays and an increase in wet MWD were observed in the highest rate of sewage sludge application. Effects of organic amendments on soil particle density, porosity, and dry MWD were not significant. Decrease in bulk density and dispersible clay content was more in the silty loam soil, while the increase in dry and wet MWD was higher in the clay soil.

Measurement of soil water content is important in hydrology, agriculture, and pedology. To this end, use of methods that can measure soil water content in a natural and safe condition with high speed and accuracy is very important. Recently, the use of Time Domain Reflectometry (TDR) has become common for quick measurement of soil salinity and volumetric water content. This study aimed to assess the effect of clay content and soil salinity on dielectric constant (volumetric water content) in saline and non-saline soils. At all five sites, both the topsoil (0-0.3 m depth) and the subsoil (0.3-0.6 m depth) were sampled. These soil samples were poured into 15-20 cylinders (sub-samples) depending on their clay content. Afterwards, pure water was repeatedly added to some sub-samples at the rate of 0.025 m3 m-3, while the others received 0.03m3m-3 saline water (EC of 0.41,0.81,1.53,2.6,3.49,4.71 dSm-1) in repeated doses until the water content was close to saturation in each subsample. The samples were then weighed and packed to reach the same bulk density as originally measured in the field. After 24-48 hrs, the TDR measurement was performed. Soil physico-chemical parameters, including organic matter, clay, silt, and sand contents and clay mineralogy were determined. The results showed that higher soil salinity increased soil dielectric constant i.e. both the rise time of the reflected signal and the total time delay increased, resulting in overestimation of soil moisture. The bound water in clay soil reduced the time delay because of its lower dielectric constant caused by specific surface area and affected on polarity of water near the particles, resulting in underestimation of soil water content. There is a turning point moisture, at which the effect of bound water is balanced by the effect of soil electrical conductivity. Also results show that only in one point linear model shows an accurate water measurement; below this point, bound water effect dominates and TDR underestimates soil moisture. Above this point, the effect of soil EC dominates and TDR overestimates soil moisture. This turning point moisture decreases as the soil salinity increases. Overall, the results show that for accurate measurement and avoidance of large errors in measurement of volumetric water content with TDR, salinity and mineralogy of clay content must be included in the calibration equation

To investigate the changes in some chemical characteristics of soil and the activities of urease and alkaline phosphatase, a randomized complete block design experiment with three replications was conducted in 2008. The main factor was fertilizer treatments (T1= no fertilizer, T2= chemical fertilizer (potassium sulfate, triple super phosphate and urea at the rate of 100, 120, 225 kg.ha-1, respectively), T3 and T5 20 Mg.ha-1 compost and vermicompost, respectively, T4 and T6, 40 Mg.ha-1 compost and vermicompost, respectively). The secondary factor was the number of years of fertilizer application i.e 2006, 2006+2007, and 2006-2008. Soil samples were taken from 0-20 cm depth at the end of 60th day of application. Organic and inorganic fertilizers were applied at seedling stage. After preparation of the soil samples, the amounts of organic matter, total nitrogen, available phosphorous, urease and alkaline phosphatase activities were determined. Results indicated that with the application of compost and vermicompost, the activities of urease and alkaline phosphatase increased and, with further increase in the amounts of organic fertilizers, the activities of the enzymes intensified. The maximum activities of urease and alkaline phosphatase enzymes was observed at, respectively, 40 Mg.ha-1 vermicompost treatment (114.00 mgN-NH3. g-1soil 2hr-1) and (33616.67 µgPNP. g-1 soil hr-1). The minimum activities of those two enzymes were recorded for the control treatment and equaled (35.79 mgN-NH3. g-1soil 2hr-1) and (1144.90 µgPNP. g-1 soil hr-1), respectively. Increasing the rate and the number of times of organic fertilizers application enhanced the amount of soil organic matter, total nitrogen, and available phosphorus, whose maxima were measured for the 40 Mg.ha-1 vermicompost treatment. Furthermore, there were signification differences among the number of years of fertilizer application in regard to enzyme activities and changes in chemical characteristics. The maximum enzyme activity and changes in soil chemical characteristics were observed in the treatment consisting of three continuous years of application.

In order to evaluate the effect of N-fixing biofertilizer, zinc sulfate, and nitrogen timing on yield and yield component and seed protein of wheat var. Pishtaz in parts of Kerman Province with temperate climate, an experiment with factorial RCB design and 3 replicates was conducted in the research farm of Shahid Bahonar University. Treatments were combinations of: (N) Nitrogen application timing (n1: 1/2 before sowing and 1/2 at tillering, n2: 1/3 at stem elongation and 2/3 at heading stage, and n3: 1/3 at stem elongation, heading, and milky stages, (ZN) Zink Sulphate (z1: 50 and z2: 0 kg/ha), and (A) Azotobacter (a1: 2 and a2: 0 kg/ha). Grain yield, number of spikes/m2, number of seeds/spike, 1000 kernel weight (TKW), and grain protein were measured. Based on the results of this study, the treatment n2z1a1 (n2:1/3in stem elongation and2/3 at heading, zn1:50 kg/ha, a1:2 kg/ha) produced the highest yield(7667 kg/ha), which had 46.74% higher yield in comparison with treatment n1z1a1(4083 kg/ha). The treatment n2z1a1 had the highest yield components including number of spikes/m2, number of seeds/spike, 1000 kernel weight (TKW) too (44.07 spikes/m2, 467 seeds/spike, and 44.61 gr, respectively) Seed protein contents as affected by the treatments in this study were significant. The highest (15%) and the least (9%) seed protein content were related to n3 a1(1/3 at stem elongation, heading, and milky stages and 2 kg/ha Azotobacter) and n1a0, respectively.

Mycorrhizal symbiosis is one of the most important beneficial interactions in terrestrial ecosystems. The positive effects of mycorrhizal symbiosis on the growth, physiology, and ecology of various plants are already recognized. However, the symbiotic relations between mycorrhizal fungi and almond with regard to nutrient uptake by this plant have not yet been explored and studied in Iran. To examine the effects of mycorrhizal inoculation on nutrient uptake by economically important native almond genotypes in Chaharmahal va Bakhtiary Province, a factorial experiment consisting of a randomized complete design with three factors: almond genotypes (Mamaei, Rabee, Talkh, Sefid), phosphorus levels (0 and 150 kg P ha-1), and mycorrhizal treatment (almond inoculated with Glomus intraradices, Glomus mosseae and without inoculation) with three replications was conducted under greenhouse conditions for 4 months. Results showed that the concentrations and uptake of immobile nutrients such as P and Zn in both root and shoot of the plant were increased in mycorrhizal almond, whereas N, Fe, and Mn concentrations showed the reverse trends in the shoot part with an increase or no significant change in their uptake. Phosphorus and Zn concentrations in plant roots were increased, whereas root Cu and K concentrations did not show significant differences between mycorrhizal and non-mycorrhizal plants. Almond genotypes indicated significant differences in nutrient uptake, but the quantity and trend of uptake varied greatly among the nutrients. Results revealed that there was no significant difference between the two fungal species in affecting almond nutrition. Briefly, results imply that the influence of mycorrhizal fungi on almond nutrition may be different and much depends upon the elements involved and their distribution between the above and below ground components of almond, while fungal species had similar effects.

One of the important components of soil management systems for sustainable agriculture is soil tillage. Tillage affects soil organisms through changes in soil properties. Hence, knowledge of short and long term effects of tillage on soil organisms is important in choosing better management systems for a sustainable agriculture. In order to investigate the short term effects of soil tillage and cow manure application on soil fauna under corn cultivation, an experiment was carried out from April until September 2008, in Grizeh Research Station of Kurdistan Province in Iran. The soil is classified as the Grizeh soil series (Fine, Mixed, Thermic, Fluventic, Xerochrepts). Treatments consisted of three tillage systems including Conventional Tillage (CT) (moldboard plow + disking), Minimum Tillage (MT) (disking), and No Tillage (NT) as the main plots and three levels of cow manure (0, 20 and 40 ton/ha) as subplots, with three replications. Experimental design was Complete Block Design (RCB) as split plot arrangement. Soil samples were collected three times during the experiment. Corn cultivar SC704 was planted as a fodder crop. Soil bulk density (BD) was measured where earthworms, springtails, mites, and nematodes populations were counted as indicators of soil macro, meso, and micro-fauna, respectively. Results showed that in short term, the effect of different tillage systems on BD was not significant and had no pronounced effects on nematodes, mites, and springtails in a loamy-sandy loam soil. However, tillage system had significant effect on earthworm population. Cow manure had positive effects on soil nematode population and corn biomass.. As a general conclusion, using MT treatment and application of 40 ton/ha cow manure were found useful management practices from agronomic and biological viewpoints.

This study was conducted to assess soil degradation status in the Abhar-Khorramdarreh Plain. A geopedologic map (soil map) was produced by integration of three information layers including the lithologic, geomorphic, and pedologic characteristics of the study area in the ILWIS environment. Information from the produced geopedologic map, together with the data extracted from the existing soil maps, was used as input to GLASOD approach to assess the susceptibility of soils to degradation. In addition to the above data layers, several other layers including the salinity map, alkalinity map, and land irrigabillity map were also produced to fulfill the requirements of the GLASOD approach. The result revealed that from a total 45,500 ha land areas studied, only 14% showed little or no evidence of degradation while the rest had varied degrees of susceptibility to degradation. Moderately and highly susceptible lands covered, respectively, 6,000 ha and about 17,000 ha. Based on the results, it is recommended to take the necessary measures to combat soil degradation in moderately and highly sensitive areas to ensure sustainable land management in the studied plain.