فهرست مطالب safoora nahidan

Phosphorus (P) is one of the most important components and a limiting factor for the growth of plants due to its low mobility and availability in soil. Application of organic materials such as biochar is one of the main choices to increase the availability of P in soil. Biochar is a carbon-rich material derived from pyrolysis of organic feedstocks under limited or no oxygen conditions. Biochar can influence the availability of P by improving the physicochemical, biological, and enzymatic conditions of soil, in addition to directly increasing the concentration of nutritional elements, particularly P. Soil pollution by heavy metals such as Cadmium (Cd) has been one of the environmental concerns in the last several decades. Cadmium alters the activity and diversity of soil microbial communities, and it also lessens soil function by decreasing the activity of enzymes related to nutrient cycling. Application of organic materials such as biochar in contaminated soil can reduce the availability of heavy metals in the soil, and as a result, increase the biological properties. It is hypothesized that application of biochar in heavy metal-contaminated soil influences the availability of P not only directly but also indirectly by improving microbial and enzymatic activity. This issue depends on the type of biochar and soil. Therefore, this study was conducted to investigate the interaction effect of biochar (cow manure and wheat straw) and Cd on microbial respiration, acid and alkaline phosphatase activity and available P in two soils with different physicochemical characteristics. A factorial experiment was conducted using a completely randomized design with three replicates. The experimental factors included 4 levels of Cd contamination (0, 5, 10 and 20 mg kg-1), 3 levels of biochar (control, wheat straw and cattle manure biochar) and 2 types of soil (corck sofla and research center). Two types of soil contaminated with different amounts of Cd from CdCl2, were amended with 2.5% of the biochar, then were incubated for 14 and 90 days at laboratory temperature and 70% field capacity. At the end of each incubation time, available Cd and P, basal respiration and acid and alkaline phosphatase activity were measured. The application of cattle manure and wheat straw biochar in soil reduced the available Cd by 70-86% and 61-85%, respectively. At all levels of Cd contamination, the amount of available Cd in the research center soil with sandy loam texture was higher than that of the Kark Sefala soil with clay texture. Higher concentrations of Cd also reduced the microbial respiration and the enzyme activities in the research center (31-46%) more than in the corck sofla (21.5-35.5%) soil. The decrease in microbial respiration and enzyme activities due to Cd contamination in the soil without biochar (10-41.5%) was more than the soil amended with wheat straw (5-39.8%) and cow manure (0.8-37.9%) biochar. The results also showed that available P increased with biochar addition and decreased with increasing Cd concentration in soil, so that the highest amount of available P was observed in the soil amended with cow manure biochar and without Cd contamination. Positive and significant correlation between available P with microbial respiration (r=0.385-0.604), alkaline (r=0.764-0.879) and acid (r=0.761-0.883) phosphatase activity was obtained, indicating that microbial activity and the enzymes involved in P cycling, play a significant role in the availability of P in the soil. These findings indicated that the application of biochar in Cd-contaminated soils can increase the bioavailability of P in the soil by decreasing the availaility of Cd and increasing microbial activity and alkaline and acid phosphatase activity. This issue was affected by the biochar and soil type.

Using efficient microorganisms can be beneficial for providing essential elements of phosphorus (P), potassium (K) and iron (Fe) to plants. In this study, the ability of some fungal species including Trichoderma asperellum, T. atroviride, T. brevicompactum, T. citrinoviride, T. harzianum, T. koningii, T. viridescens, Alternaria sp. and Aspergillus niger to release of these elements from insoluble minerals was evaluated. For this, the fungal species were added to Aleksandrov medium including tricalcium phosphate (P source) and muscovite or phlogopite (K and Fe source) and were incubated for 10-days under optimum conditions. The results showed that fungal species were able to release K from phlogopite by 103-389% and from muscovite by 21.5-178% compared to control. Among fungal species, the highest and lowest K release was observed by Aspergillus niger and T. koningii from phlogopite and by T. atroviride from muscovite, respectively. Also, the highest and lowest amount of soluble Fe was observed in medium with T. citrinoviride and Aspergillus niger in the presence of phlogopite and with T. atroviride in the presence of muscovite, respectively. The highest increase in soluble P was observed by Aspergillus niger (in the presence of both minerals), Alternaria sp., T. citrinoviride, T. coningii and T.viridescens in the presence of phlogopite compared to the control. Fungal species increased the electrical conductivity, indicating the release of elements from insoluble sources by the fungi species. There was also a significant negative relationship between P, K and Fe with pH, indicating that fungal species may have been able to release elements from the insoluble sources by producing organic and inorganic acids. In general, the fungal species have the ability to dissolve tricalcium phosphate and release more K and Fe from phlogopite than muscovite under in-vitro conditions. Thus, application of these microorganisms can be promising to provide the essential elements of plants.

Traditional organic manure can be potentially beneficial for soil physical, chemical and biological properties by improving organic matter of soils. Recently, biochar, a carbon rich product of biomass produced by thermochemical conversion under oxygen-limited conditions, has been studied for its effects as a soil amendment. The use of a modified form of manure as manure biochar for soil improvement reduces some environmental, food safety and disposal problems of manures. However, biochar application has been shown to have a positive and negative effect on soil fauna such as earthworm depending on the type of feedstock for its production. Since earthworm function affects physical properties and amount of organic carbon of soils and because of the different effect of biochar and its feedstock on earthworm activity, this study hypothesizes that earthworm may differently alter soil physical properties and aggregates associated carbon in the biochar and its feedstock amended soils. The purpose of this study was to investigate the effect of cow manure and its biochar in the presence and absence of earthworm on bulk density, total porosity, saturated hydraulic conductivity, aggregate stability and content of organic carbon in soil aggregates during 30 and 90 days incubation.

A completely randomized design with 2×4×2 factorial treatment combination was used in triplicates. Treatment variants examined in this study included the following: (i) 2 levels of amendment type (cow manure and its biochar), (ii) 4 levels of applied amendment rate (0, 1, 2 and 5%), (iii) 2 levels of earthworm (with and without earthworm). The biochar was produced from cow manure (passed through 2 mm mesh) by slow pyrolysis at 450 °C. For this experiment, the soil sample was passed through 4 mm mesh. Then, amended soil and the control were moistened up to 70% water holding capacity. Then 5 adult Eisenia fetida with fully-developed clitellum and similar weight were added to half of them. Treatments were then incubated at laboratory temperature and constant moisture for 30 and 90 days. Based on evaporation loss, the soil moisture was kept constant by regular weighing of each pot. At the end of each time (30 and 90 days), samples were taken from different treatments to determine bulk density, total porosity, saturated hydraulic conductivity. Also, soil aggregates were separated by wet sieving, then aggregate size distribution was determined and mean weight diameter (MWD) was calculated, also organic carbon content in each aggregate size fraction was determined.

The results showed that the application of both organic amendments was effective in decreasing soil bulk density, increasing total porosity, saturated hydraulic conductivity and aggregate stability, but the effects of organic amendments on these physical properties were more pronounced in cow manure- than biochar-amended soils. Further reduction in bulk density following manure application is attributed to a dilution effect, resulting from mixing of the lighter material of manure with denser mineral fractions of the soil. In addition, cow manure has more content of organic carbon than its biochar which can increase total porosity by promoting aggregation. The greater porosity and aggregation of soils as affected by the application of organic amendments are apparently responsible for the increased saturated hydraulic conductivity. The results showed that the effect of cow manure on the soil physical properties reduced with time more rapidly than its biochar. It might be attributed to lower stability of manure to degradation than biochar in soils because manure contains higher content of labile organic compounds compared to biochar. Our results also showed that application of organic amendments led to increase organic carbon in soil aggregates, especially in 4-2 mm aggregates, indicating that the large macro-aggregates can be considered as a susceptible indicator to organic carbon managements in soil. Also, the organic carbon content of 4-2, 2-0.25 and 0.25-0.05 mm aggregates was 42.8, 27.8 and 20.8% (in 30 days incubation) and 27.2, 28.6% and 20.6% (in 90 days of incubation) higher in cow manure- than biochar-amended soils. The results also showed that earthworm reduced soil bulk density, increased total porosity, saturated hydraulic conductivity and aggregate stability regardless of soil amendment but such effect on bulk density and total porosity was more pronounced in cow manure- than biochar-amended soils. It means that type of organic amendments can influence on earthworm activity, thereby altering some soil physical properties. Also, earthworm led to increase carbon content in soil aggregates, especially in smaller aggregates.

The results showed that although application of cow manure improved soil physical properties more than cow manure biochar at both incubation times, it seems that cow manure biochar has a more stable effect on the soil physical properties over time. Also, application of organic amendments can lead to increase soil organic carbon by further increasing C in larger aggregates. Other results indicated that the improving effect of earthworm on soil physical properties (except for bulk density and total porosity) did not depend on the type of applied organic amendment in soil. The effect of earthworm on bulk density and total porosity was more pronounced in soils amended with cow manure than its biochar. Also, it is thought that earthworm increases organic carbon in soil by physical stabilization of organic carbon in soil aggregates, especially in smaller aggregates.

The deficiency of macro-nutrients such as phosphorus and potassium is very important due to vital roles of these elements. Although the total amount of phosphorus and potassium in the soil is high, the formation of insoluble forms of phosphorus, as well as the stabilization of potassium in silicates, has led to the shortage of these essential elements. The use of microorganisms, having the ability to dissolve insoluble phosphate forms and potassium fixed in silicates, can be effective in reducing the deficiency of these elements for the plant. In this research, 7 species of Trichoderma fungis were selected and their effects on the release of phosphorus and potassium were evaluated in Pikovskaya’s, Alexandrov’s and modified Pikovskaya’s media. The results showed that in Pikovskaya’s broth medium, phosphorus release rate by different species of fungi was consistent with decreasing pH. Trichoderma koningii, T.harzianum, T.citrinoviride and T.viridescens had the most phosphate solubilizing ability and increased soluble phosphorus by 244, 205, 191 and 190%, respectively. In both Aleksandrov’s and modified pikovskaya’s media, which contain both insoluble inorganic phosphate and potassium as biotite, it was observed that the dissolution rate of tri-calcium phosphate was lower than that of pikovskaya’s medium which has available potassium. T.koningii in Aleksandrov’s medium and T.harzianum in modified Pikovskaya’s medium had the highest ability to release potassium from biotite. These species increased potassium in solution by 123 and 20% compared to control, respectively. In general, the results showed that Trichoderma fungi has the ability to solubilize phosphate from tri-calcium phosphate and release potassium from biotite under in-vitro conditions.

Little is known about the effects of biochar on earthworms and their interactions on soil biological properties. The purpose of this study was to investigate the effects of earthworm and cow manure biochar (compared to cow manure) on some biological properties of soil. For this purpose, the soil was treated with cow manure or its biochar in 4 levels (0, 1, 2 and 5%) in the absence and presence of earthworm and incubated for 30 and 90 days. The results showed that the number of earthworm decreased in soil treated with cow manure biochar in 30 days of incubation. After 90 days of incubation, application of 1, 2 and 5% cow manure increased the number of earthworm by 26, 91 and 104%, respectively. Application of 1% biochar resulted no significant effect on the number of earthworm, but the 2 and 5% biochar decreased the number of earthworms by 43 and 48%, respectively. The results showed that the earthworm led to considerable increase on the basal respiration, substrate induced respiration and microbial biomass carbon in soils treated with cow manure compared to cow manure biochar. Also, application of both amendment improved the soil biological properties compared to the control. On the other hand, earthworm increased and decreased the metabolic quotient in 30 and 90 days incubation, respectively. The addition of cow manure and its biochar reduced the metabolic quotient in 90 days of incubation. In addition, the soil treated with 5% cow manure and earthworm (in 90 days) had the lowest metabolic quotient. Overall, cow manure improved soil biological quality better than cow manure biochar. However, application of 1% cow manure biochar in the soil which has no negative effect on earthworm, can be also beneficial to improve soil biological quality.

In recent year, application of biochar in soils of dry and semi-arid regions has been considered for increasing soil organic carbon. However,  few reports are available about the effect of biochar on nitrogen cycling in such soils. The purpose of this study is to investigate the effects of cow manure and its biochar on some N cycling processes and related biological properties in a calcareous soil. For this purpose, 0, 1, 2 and 5% of cow manure and its biochar were added to a calcareous soil and then the treated soils incubated for 30 and 90 days. The results showed that the microbial biomass nitrogen and urease activity in the soils treated with cow manure increased more intensively against the soils treated with biochar. The application of 2 and 5% of biochar increased the nitrogen mineralization by 20.5 and 32.3% at 30-days incubation, and by 103 and 106% at 90-days incubation. Addition of cow manure to soil led to a significant increase in nitrogen mineralization by 38-233% at 30-day incubation and 21- 105% at 90-day incubation. At 30-days of incubation, nitrification increased in soils treated by 5% of biochar. The addition of biochar to the soil increased nitrification by 10-50% compared to the control at 90-days of incubation. The addition of cow manure to soil increased nitrification by 1500-300% and 39-95% in comparison to the control after 30 and 90 days of incubation. In general, our findings showed that the use of cow manure biochar compared with cow manure could reduce nitrogen mineralization and nitrification and prevent rapid nitrate leaching.

Introduction Conservation and improvement the soil structural stability play a key role in soil management in agro ecosystems especially in arid and semiarid region with high erosion potential. Soil structure is an important soil physical property and has many effects on other soil physical, chemical and biological behaviors such as retention and movement of water, nutrients and pollutions, soil hydraulic and mechanical properties, soil aeration and erosivity. Wetting and drying cycles are one of important environmental factor affecting soil structural stability. Previous studies showed inconsistent results about the positive or negative effects of wetting and drying cycles on soil stability. This study was conducted to investigate the effect of wetting and drying cycles on the soil structural stability in the presence of safflower residues. Materials and Methods The agricultural soil was collected from the soil surface layer (0–20 cm) of Shahrood in Semnan province and passed through a 4 mm sieve. An experiment was conducted including two treatments i.e. number of wetting and drying cycles (0, 1, 2, 4, 8 and 10 cycle) and amount of safflower residues (0, 1 and 2 g 100 g-1 soil ). Plant residues were collected from safflower fields and after drying, milled and passed through a 1 mm sieve. Then crop residues were mixed into soil. The wet and dry cycles were applied during 2 month. In wetting periods the soil was kept in filed capacity and in dry periods the soil was kept in electrical oven in 40°C. The soil organic carbon and soil diluted acid carbohydrate concentration were measured at the end of the experiment. The soil structural stability was measured using high energy moisture curve. The soil drainable pores, soil suction at inflection point, stability index, stability ratio and Dexter's S index were calculated. Results and Discussion The greatest soil organic carbon was observed in control treatment (0 wet and dry cycle) and then it was decreased by increment of cycles in all crop residues levels. These cycles improve the microbial activity during the rewetting process and increase decomposition of crop residues. The soil organic carbon and diluted acid carbohydrate were highest in treatments including 2 g residues 100g-1 in all studied wet and dry cycles. The greatest soil drainable pore volume and the lowest soil suction at inflection point were found in treatment including 4 wet and dry cycles. The results showed that 2 and 4 cycles increased the soil drainable pore volume by 58 and 106 % compared to the control treatment (no applied cycle). More increment of wet and dry cycles decreased the soil drainable pore volume and this factor was declined by 40 % in 10 cycles treatment compared to 4 cycles. It means that wet and dry cycles can improved the soil structure because of rearrangement of soil particles and improvement of soil particle contact points. However, the high number of wet and dry cycles destructed the aggregate and decreased their stability. In addition, the physical protection of soil aggregates from soil organic matters declined through aggregate breakdown. This phenomenon provided fresh organic matter for decomposers and consequently the aggregate stability decreased. Appling only one wet and dry cycle could not significantly improve the stability ratio. This ratio improved considerably when 2 and 4 cycles were used. Following the aggregate breakdown in treatments including more than 4 cycles, the stability ratio decreased in all crop residue levels. Our results showed that the greatest and the lowest volume of coarse and medium pore were observed in 4 and 10 wet and dry cycles treatments but the greatest and the lowest volume of fine pores were observed in 10 and 4 wet and dry cycles treatments. It means that the structural stability improvement during 0-4 cycle changed the pore distribution and made larger pores but the aggregate breakdown with more than 4 cycles changed the pore volume again and increased the portion of finer pores. Conclusion Our results showed that the low number of these cycles can improve the soil aggregation and aggregate stability but the high number of these cycles has negative effect on aggregate stability. However, the presence of organic matter in soil can decreased the negative effect of wet and dry cycles. These results confirmed the importance of incorporating crop residues in to the soils after crop harvest.

There is a close relationship between microbial activities and soil physical environment. The specific location of each enzyme within the soil matrix has been attributed to the location of their substrates, enzyme characteristics or the organisms responsible for their production. Topography (slope position), one of the important soil forming factors, plays a significant role in development, evolution and variability of soils. Landscape-scale variations in soil enzyme activities are controlled by pedological and hydrological processes. The effect of topography (slope position) on aggregate size distribution and the enzyme activities has been evaluated in previous studies. Slope position may influence the aggregate distribution of acid and alkaline phosphomonoesterase differently. Therefore, the objective of this research is to evaluate the aggregate distribution of acid phosphatase and alkaline phosphatase activities in different slope positions.
Soil samples were collected from three slope positions of a grassland ecosystem. At each landscape position, three equally spaced points were selected, at a distance of 10 m. In each point, ten soil cores of 0–10 cm depth were taken within a 2 m radius and then composited. After measuring general properties in soil, aggregates were separated by wet sieving method. The aggregates remained on each sieve were collected and weighted. Organic C, available phosphorous, acid phosphatase and alkaline phosphatase were measured in the six size ranges (4–2, 2–1, 1–0.5, 0.5–0.25 and 0.25–0.05,
Results showed that aggregate size distribution was influenced by slope position. Microaggregates were lowest and greatest in summit and backslope positions, respectively. Macroaggregate contents were related by organic C along slope position. Macroaggreagtes decreased in backslope positon by 85%. The results also showed that organic C and available P were greater in macroaggregates than microaggregates by 38 and 12% respectively. Both acid phosphatase and alkaline phosphatase activities were greater in macroaggregates than microaggaregates and their activities decreased with decreasing aggregate size by 42%. The effect of slope positon on the distribution pattern of phosphomonoesterase was different. Acid phosphatase and alkaline phosphatase activities were lowest in toeslope and backslope, respectively. Although, acid phosphatase to organic C and available P was higher in all aggregates of backslope position, the distribution pattern of alkaline phosphatase to organic C and available P in different slope positions was dependent to aggregate size. Alkaline phosphatase was only related to available P (r=0.72 P=0.001).
In overall, acid and alkaline phosphatase activities had similar distribution in soil aggregates but both enzymes were distributed differently in different slope positions. Since macroaggregates contain higher organic C, available P and phosphomonoesterase activities, soil structure protection of sensitive slope positions to erosion can influence on P cycling in soil.

The location of extracellular enzyme activities in soil aggregates can be influenced by slope position. This study aims to determine the effect of slope position on aggregate distribution of organic C and L-glutaminase activity. The soils were collected from different slope positions (shoulder, backslope, footslope and toeslope) at two pasture ecosystems (Fereydoonshahr and Chelgerd, central Iran). A wet sieving procedure was used to separate soil aggregates and then mean weight diameter (MWD) was calculated. Soil organic C (SOC) and L-glutaminase activity (LGL) were measured in the separated aggregates. Results indicated that slope position influenced aggregates distribution and stability through its effect on soil physico-chemical properties. The LGL activity significantly influenced by slope position which was consistent with the pattern of SOC content (Fereydoonsahr: r=0.7, P