yaser azimzadeh

Chickpea (Cicer arietinum L.), a key legume of the Fabaceae family, is cultivated as a winter or spring crop, primarily under rainfed conditions, in western and northwestern of Iran. To position chickpea as a viable alternative in cereal-based rotations and enhance its contribution to sustainable agriculture, agronomic practices—especially nutrient management—must be thoroughly optimized and studied.  Nitrogen (N), the most critical macronutrient for plant growth and yield enhancement, is required in greater quantities than any other element. While chickpea fulfills much of its nitrogen demand via biological nitrogen fixation (BNF), a minimal "starter" N dose is essential to ensure robust seedling establishment and meet early growth requirements before effective rhizobial symbiosis is achieved. Precise determination of starter N for rainfed chickpea is critical, as excessive application increases costs, risks environmental contamination, and suppresses yields, whereas insufficient doses compromise productivity. 

A randomized complete block design (RCBD) with three replications was employed during the 2022–2023 growing season to evaluate the N requirements of rainfed chickpea (cv. Ana) under cold rainfed conditions in Bukan (autumn sowing) and Maragheh (autumn and spring sowing). Treatments included five urea levels: 0, 25, 50, 75, and 100 kg ha⁻¹. Following reduced tillage (using a combination tillage implement), chickpea seeds were sown at 40 seeds m⁻². Autumn sowing occurred in October 2023, and spring sowing in late February 2024, using an ASKE 3-shank 11-row planter with 53–17 cm row spacing. Experimental plots measured 10 × 30 m. Urea was applied via subsurface banding (5–6 cm below seeds) at sowing. Measured parameters included root traits (length, volume, dry weight, nodule weight), plant height, 100-seed weight, biological yield, grain yield, harvest index, and rainwater use efficiency. 

Environmental effects significantly influenced root length, nodule weight, root volume, dry weight, plant height, biological yield, grain yield, rainwater use efficiency (p ≤ 0.01), and 100-seed weight (p ≤ 0.05). Nitrogen levels significantly affected all parameters (p ≤ 0.01), except 100-seed weight (p ≤ 0.05). Autumn-sown Bukan exhibited superior root traits, plant height, and yields compared to Maragheh. Root length, volume, and dry weight declined with increasing N, likely due to restricted root growth from urea banding at higher doses. Enhanced nodulation in Bukan may reflect its soil’s native rhizobia populations, as Maragheh lacks prior legume cultivation. Elevated soil fertility and favorable climatic conditions in Bukan further supported root development. Excessive mineral N inhibited rhizobial symbiosis, reducing nodule weight. Plant height and 100-grain weight peaked at 50 kg ha⁻¹ N in Bukan (57 cm, 6 cm above control). In autumn-sown Bukan, grain yield plateaued at 25 kg ha⁻¹ N, while Maragheh achieved maxima at 75 kg ha⁻¹ (autumn) and 50 kg ha⁻¹ (spring). The highest harvest index (48%) occurred at 50 kg ha⁻¹ N in spring-sown Maragheh. Starter N bolstered early growth and photosynthetic capacity, enhancing yields. Moderate N optimized harvest index by favoring grain over biomass allocation. Rainwater use efficiency (RUE) was higher in autumn-sown chickpea in Bukan compared to both autumn- and spring-sown crops in Maragheh. Furthermore, RUE initially increased with rising nitrogen application rates but declined at elevated doses. Regression analysis of grain yield against urea application rates revealed maximum achievable yields of 1535 and 940 kg ha⁻¹ for autumn-sown rainfed chickpea in Bukan and Maragheh, respectively. To attain these yields, starter urea doses of 62 and 61 kg ha⁻¹ were required for Bukan and Maragheh. For spring-sown chickpea in Maragheh, the peak grain yield was 835 kg ha⁻¹, achievable with a urea input of 43 kg ha⁻¹. The minimal urea requirements for maximizing net economic returns were 60 kg ha⁻¹ for autumn-sown chickpea in both regions, whereas spring-sown systems in Maragheh required 42 kg ha⁻¹. Simple correlation analyses between grain yield and yield components demonstrated that grain yield showed the strongest positive correlations with biological yield, plant height, and root dry weight, in descending order of magnitude. Similarly, rainwater use efficiency exhibited the highest positive correlations with grain yield, biological yield, and plant height, respectively. The robust correlations between grain yield and these traits suggest that these parameters likely exert direct influences on grain yield. 

Excessive nitrogen fertilization leads to salinity, toxicity, and disruption of symbiotic relationships, offsetting potential yield benefits. A minimal starter dose of 42 kg ha⁻¹ urea is sufficient for spring-sown chickpea, while 60 kg ha⁻¹ urea maximizes economic returns in autumn-sown systems. Precision in N management is critical to balance productivity, sustainability, and environmental stewardship in rainfed chickpea cultivation.

Field pea (Pisum sativum spp . arvense L.), as a legume crop is a viable alternative crop that can be integrated into cropping rotations with cereals within dryland farming systems. However, crop production under rainfed conditions, which is highly dependent on climate, is associated with high risk due to weather fluctuations and uncertainty. Therefore, identifying the optimal levels of manageable factors is essential for effectively mitigating the risks associated with environmental factors, particularly those related to climatic conditions. In the present study, the effects of managerial factors, including sowing date, sowing depth, and plant nutrition, on the yield of forage pea were investigated through a split-plot factorial experiment conducted with three replications. This study was carried out over two growing seasons, 2022-23 and 2023-24, at the Dryland Agricultural Research Institute (DARI) located in Maragheh. The main plots consisted of two planting dates (Entezari or dormant seeding, and spring), while factorial combinations of fertilizer application at two levels (application and no application) and sowing depth in three levels (3, 6 and 9 cm) were assigned in sub-plots. Forage yield was significantly affected by planting date, sowing depth, and fertilizer application. The optimal sowing depth was determined to be 6 cm. Additionally, optimal plant nutrition significantly improved forage yield. In the first year, the forage yield associated with the Entezari sowing date was marginally superior to that of the spring sowing. However, in the second year, the yield from the spring sowing date was significantly higher than that from the Entezari sowing date. In general, while Entezari planting can extend the crop growth period and optimize the use of environmental resources, the simultaneous emergence of pests, such as cutworms (Agrotis spp.) and leaf beetles, during years when outbreaks are possible can cause significant damage and reduce crop yields compared to spring planting.

Biochar can reduce the plants vulnerability to diseases with different mechanisms such as improving soil fertility, increasing the population and activity of beneficial microorganisms, limiting the activity of pathogens, absorbing toxins produced by pathogens, stimulating the production of antibiotics, inducing plant systemic defense and changes in root exudates. The role of biochar in reducing plant diseases depends on the biochar properties, biochar dosages, soil properties, crop, and the type of pathogen. The biochar properties are affected by the type of biomass and production temperature. In addition, the mechanisms of biochar to protect the plant against each type of pathogens may be different. Therefore, considering the importance of biomass type and carbonization temperature in the efficiency of biochar, it is suggested to pay more attention to the ability of biochars produced from different biomasses and temperatures to reduce plant diseases.

Climate change phenomenon is one of the most important global challenges for mankind in providing sufficient and healthy food for the ever-increasing world population. The leading factors of climate change, such as increasing temperature, changing precipitation patterns, and increasing the frequency and intensity of weather events, affect soil characteristics, especially in the ecosystems of arid and semi-arid regions. These changes can directly affect the growth and production of crops. The amount of soil organic matter is one of the most important indicators of soil quality and health, which affects many physical, chemical and biological characteristics of soil and is directly and indirectly affected by climatic factors such as temperature and rainfall. On the other hand, the balance of input and output of organic carbon to the soil is effective on the amount of carbon dioxide in the atmosphere and thus on global warming and the climate change phenomenon. The results of many forecasts show that in arid and semi-arid regions, climate change will lead to an increase in temperature and a decrease in rainfall. Therefore, considering that the amount of organic matter in the soil decreases with the increase in temperature and decrease in humidity, it seems that the phenomenon of climate change will have adverse effects on the amount of soil organic matter and biological activity, and then on the production of crops in arid and semi-arid regions. Therefore, it is very important to use the necessary solutions to mitigate these adverse effects and adapt to the upcoming conditions. Mitigation refers to methods that lead to the reduction of greenhouse gas emissions, especially carbon dioxide; But the goal of adaptation is to mitigate the inevitable effects of climate change. Based on the results of various publications, compliance with the principles of the conservation agriculture system is considered one of the most important mitigation and adaptation solutions in dealing with the consequences of climate change in arid and semi-arid regions. Due to the fact that the climate change phenomenon is an inevitable event and its adverse effects and consequences in human life are felt more and more intense day by day, it is necessary for the management of soil resources to have the necessary foresight regarding the results of this phenomenon on the quality of the soil and the potential of producing agricultural products, especially in Arid and semi-arid areas should be considered.

Biochar is a black solid containing stable carbon with many positive effects on the physical, chemical, and biological properties of soil. One important positive effect of biochar on soil is its contribution to nutrient (e.g., nitrogen) mobility and dynamics in soil. Negatively charged on the surface, biochar is capable of adsorbing and storing ammonium ions (NH4+) and small nitrogen-containing organic molecules. It also releases nitrogen into the soil to change the carbon to nitrogen ratio (C/N), whereby the mineralization-immobilization balance of nitrogen is affected. Moreover, biochar indirectly affects soil nitrogen cycle and dynamics by changing such soil properties as pH, cation exchange capacity, electrical conductivity, organic carbon, biological activity, nutrient availability, porosity, ventilation, and water relations, among others. It is through these changes that water, air, and nutrients are provided to make soil a suitable habitat favorable to soil microorganisms that help improve biological fixation of nitrogen. Biochar also reduces N2O emission, as a greenhouse gas, from the soil by reducing soil nitrogen sublimation. In general, biochar has a synergistic interaction with nitrogen and can enhance nitrogen use efficiency to reduce nitrogen fertilizer consumption. However, only scant knowledge is presently available on soil nitrogen changes induced by biochar, especially in calcareous soils. Further research is needed to investigate the effects of biochars produced from different types of biomass under different temperatures on the mobility and availability of nutrients, especially nitrogen, in calcareous soils.

Biochar is a carbon-rich charcoal material resistant to decomposition, which is produced by heating biomasses in an oxygen-free environment or with limited oxygen. It is used with the aim of increasing organic carbon and improving the physical, chemical and biological characteristics of the soil. Thus its use in the low-fertile soils of hot and dry regions of Iran, which are often deficient in organic carbon, is important. Addition to its high stability in the soil, biochar can sequester atmospheric carbon dioxide in the soil for several hundred to several thousand years. In addition, it can improve soil fertility for a long time by affecting its physical, chemical, and biological properties. The stability of biochar is affected by several factors, such as the characteristics of biochar and soil, the interaction of biochar with soil components and environmental factors, which are examined in this article. Therefore, it is important to use biochar in the soils of arid and semi-arid regions of Iran, which are often deficient in organic carbon.

In this review article, while investigating the evidences of the high stability of biochar in the soils, the   most effective factors the fate of biochar in the soil, including the mechanisms of biochar removal from the soil, biochar stabilization in the soil, and interactions of biochar with soil components, and the gaps and required research areas are presented.

Biochar is higher resistant to degradation than the original carbon compounds in biomass. However, by interacting with soil components, biochar undergoes changes over time and is removed from the soil. The intensity of these changes and biochar residence time in the soil depends a lot on the type of biochar; So, biochars produced from grassy biomass and biochars produced at low temperatures are less stable. In addition, biochar interacts with all soil components, including organic matter, mineral particles, nutrients, living organisms, and soil water and atmosphere, and the result of these interactions determines the stability of biochar in soil. External factors such as the presence of plant and induced root changes, wind and water erosions, leaching, and fire also affect the fate of biochar in the soil. Among these, considering the interactions between microorganisms and biochar in soil, it seems that soil microorganisms play the most important role in the decomposition and destruction of biochar in soil. However, mechanisms such as the entrapment of biochar particles inside aggregates, binding of biochar with organic and inorganic components of soil, and inactivation of soil enzymes by biochar can increase the stability and durability of biochar in soil.

Considering the very high stability of biochar in soil and the necessity of increasing soil organic carbon as the main factor of soil fertility factor, the use of biochar in Iranian soils it can directly and indirectly improve the fertility of these soils while increasing soil organic carbon. However, after biochar is added to the soil, it interacts with the soil components and its characteristics change and evolve over time (aging). However, due to the novelty of biochar technology and the wide range of its application fields, our information on its interactions with various soil components, its long-term changes and developments in the soil and environment, and its long-term effects on the soil and the environment are not yet clearly defined and much research is needed in this field.

More than 80% of Iran's area is arid and semi-arid. Arid and semi-arid soils have various problems and limitations. One of the most important factors limiting soil fertility and crop production in these areas is the lack of soil organic matter (SOM). In more than 60% of Iran's agricultural lands, the amount of SOM is less than 1%; While its optimal level in soils should be 2-3%. SOM, as one of the most important indicators of soil health, plays a vital role in soil fertility and crop production; So, by increasing the amount of SOM, the physical, chemical, and biological characteristics of the soil and crop yield can be improved. However, the stability and residual effects of the fertilizers and organic wastes in the soil are low. Nowadays, converting organic wastes and residues into biochar and adding them to the soil is one of the new methods of increasing soil organic carbon, which enhance soil fertility and crop yield and has high residual effects due to its high stability. However, due to the specific characteristics of the soils of arid and semi-arid regions, using biochar in these regions is associated with challenges and has received less attention. In this review article, while reviewing the positive effects of biochar on soil quality indicators and crop production, the challenges of using biochar in the soils of arid and semi-arid areas, especially in drylands, and the solutions to overcome these challenges have been reviewed.

Climate change is one of the most significant global challenges threatening food security now, in the near and far future. This mainly occurs in the form of increasing temperature, change in rainfall pattern, and increase in extreme weather events. There are strong evidences demonstrating the vulnerability of agriculture sector in arid and semi-arid regions to climate change. This may directly impact on crops growth and production or indirectly impact on their environments. The ability of soil to produce a crop depends on its physical and chemical properties and these properties are directly and indirectly affected by climatic factors such as temperature and rainfall. Most predictions show that in arid and semi-arid regions, including many regions of Iran, climate change will lead to an increase in temperature and a decrease in rainfall. Therefore, considering the importance and role of temperature and humidity in physical and chemical quality indicators of soil and production stability, it seems that the phenomenon of climate change will have adverse effects on soil and then on crop production. Therefore, it is very important to use the necessary solutions to mitigate these adverse effects and adapt to the upcoming conditions. In this article, by reviewing and summarizing the research on the effects of climate change on the characteristics of arid and semi-arid soils, an attempt has been made to provide some kind of foresight of possible changes in the physical, chemical, and biological properties of soil due to climate change.

Layered double hydroxide functionalized biochar and hydrochar composites are environmentally friendly and low-cost adsorbents for the removal of phosphate from aqueous solutions. In the present study, Mg-Al layered double hydroxide functionalized apple wood biochar and hydrochar were prepared and their phosphate adsorption characteristics were examined through batch experiments. Moreover, important factors affecting adsorption including initial phosphorus concentration (25-200 mg/L), contact time (5-120 min), ionic strength (deionized water, and 0.001, 0.01, and 0.1 mol/L KCl), pH (3-10), and adsorbent dosage (1, 2, 3, and 4 g/L) were investigated. Based on the results, the phosphate adsorption by Mg-Al layered double hydroxide modified biochar and hydrochar were comparable with Mg-Al layered double hydroxide and were greater than biochar and hydrochar. As expected, phosphate adsorption was decreased by increasing solution pH and ionic strength. The highest phosphate removal was attained at pH 4, adsorbent dosage of 4 g/L, and in the presence of deionized water as a background solution. Determination of adsorption characteristics of the adsorbents revealed that the phosphate adsorption mechanism involved a combination of electrostatic attraction, interlayer anion exchange, and formation of surface complexes. The Mg-Al layered double hydroxide modified biochar and hydrochar composites as cost-effective and efficient adsorbents suggest alternative biochar- and hydrochar-based composites for the phosphate removal from contaminated waters that could be used as P-fertilizers.

Biochar and hydrochar are carbonacious solid materials that produced through carbonization of biomasses, resulting in carbon sequestration and soil fertility improvement. The aim of this study was converting different biomasses including sewage sludge, poultry manure, sugar beet tailing, wheat straw, and apple wood wastes to biochar and hydrochar and investigating their chemical properties. Also, using a factorial experiment on the basis of completely randomized design with three replications, ‎the effects of the apple wood biochar and hydrochar were studied in the presence and absence of monocalcium phosphate fertilizer‎ on soil pH and EC and available P, K, and Na. A slow pyrolysis process with a temperature of 500 ºC for 1 h was employed to produce the biochar and a hydrothermal carbonization process with a temperature of 180 ºC and pressure of 11 bar for 12 h was applied to produce the hydrochar. After conversion of biomasses to biochar and hydrochar, yield percentage of the biochars and hydrochars and pH, EC, ash percentage, and concentrations of N, P, K, Ca, Mg, Na, Fe, Mn, Cu, and Zn in initial biomasses, biochars, and hydrochars were measured. The results showed that the ash percentage and elements concentrations in biomasses, biochars, and hydrochars of poultry manure and sewage sludge were greater than those of sugar beet tailing, wheat straw, and apple wood. The pH of all biochars was more than 7, and the pH of all hydrochars (except for the poultry manure-derived hydrochar) was less than 7. Application of wood biochar increased soil pH and the integration of P-fertilizer with hydrochar decreased soil pH. The soil pH and EC in presence of hydrochar were lower than those of biochar with and without P-fertilizer. The P-fertilizer had synergistic interactions with biochar and hydrochar‎ in terms of soil available-P. The effects of biochar, hydrochar, and P-fertilizer application on soil available- potassium and sodium were not significant. Regarding the acidic pH of the studied hydrochars and increased concentrations of some nutrients in the investigated biochars and hydrochars, the applications of biochar and hydrochar accompany with P-fertilizer could be recommended in calcareous soils.

Phosphorus (P) is an essential element for living organisms. Discharging P from various sources, such as industrial wastewater and agricultural waters, into surface water causes eutrophication and undermines the balance of aquatic ecosystems and imposes many costs due to water quality degradation. In addition, mineral resources of P-fertilizers in the world are unrecoverable and are coming to an end. Therefore, it is very important to develop adsorbents to remove P from contaminated water and then be used as P-fertilizer for surmounting the eutrophication and P-fertilizer exhausting challenges. In the last few years, biochar and hydrochar have been considered as low-cost porous eco-friendly adsorbents with a high surface area and easy to produce and use. Biochar and hydrochar are carbonaceous solids that are produced from the carbonization of biomasses and could be used as adsorbents and soil amendments. However, because of their high negative charge and very low ability to absorb anions, especially phosphate, they cannot be used as phosphate adsorbents. In recent years, several methods have been introduced to change the surface of biochar and hydrochar to increase their anion adsorption capacity. In this respect, the successful results of the production and the use of engineered biochars, such as layered double hydroxides (LDHs) functionalized biochar (LDH-biochar) and LDH-hydrochar composites have been provided. Layered double hydroxides (LDHs) are brucite-like compounds with a large specific surface area, high positive charge, and exchangeable interlayer anions. LDHs functionalized biochar and hydrochar composites are environmentally friendly adsorbents for the removal of phosphate from aqueous solutions. Also, P-loaded LDH-biochar and LDH-hydrochar composites have the potential application as a P-fertilizer. These composites may increase soil available-P through the slow release of P and can improve soil properties and fertility due to the presence of the biochar and hydrochar in their structure. So, the P-loaded LDH-biochar and LDH-hydrochar may affect the availability of soil nutrients and plant growth. Nitrogen (N), P, and potassium (K) are the macronutrients that have a direct and great influence on plants growth. Therefore, the aims of this study were: (I) producing LDH-biochar and LDH- hydrochar composites and loading them with phosphate. (II) Investigating the effects of the biochar, hydrochar, LDH, LDH-biochar, LDH-hydrochar, the P-loaded LDH-biochar (LDH-biochar-P), and LDH-hydrochar (LDH-hydrochar-P) on dry matter and concentrations of P, N, and K in corn shoot and root. Biochar was produced from applewood feedstock through slow pyrolysis at 600 ºC for 1 h under Argon flow conditions. Hydrochar was produced through hydrothermal carbonization of the applewood feedstock at 180 ºC and 11 bars pressure for 12 h. Then by precipitation of LDH particles on the biochar and hydrochar surfaces, LDH-biochar and LDH-hydrochar composites were prepared. The LDH particles were synthesized via a combined fast co-precipitation and hydrothermal treatment route. Each gram of LDH-biochar and LDH-hydrochar composites was loaded with 51 and 47 mg P, respectively. Then using a factorial experiment on the basis of completely randomized design with three replications, the effects of biochar, hydrochar, LDH, LDH-biochar, LDH-hydrochar, LDH-biochar-P, and LDH-hydrochar-P were studied in presence and absence of monocalcium phosphate fertilizer on corn dry matter and concentrations of N, P, and K in corn shoot and concentrations of P and K in corn root. The results showed that the biochar had a higher yield and ash percentage, pH and electrical conductivity (EC) as compared with the hydrochar. The concentrations of all studied nutrients in the biochar, except for N, were greater than those of hydrochar and biomass. The P, K, Na, Fe, Mn, and Zn concentrations in biochar and hydrochar were significantly greater than the initial biomass. The application of P-fertilizer increased root and shoot dry matters in all treatments, except for LDH-biochar-P and LDH-hydrochar-P treatments. Biochar and hydrochar had no significant effects on root and shoot dry matter in non-P-fertilized treatments and had no significant effects on P and K concentrations of corn root and shoot. However, biochar and hydrochar increased shoot dry matter in P-fertilized treatments. The highest root and shoot dry matters, P concentrations of root and shoot, and N concentration of shoot were obtained in the presence of the LDH-biochar-P and LDH-hydrochar-P, and the lowest root and shoot dry matters of corn were observed in the presence of the LDH. Application of P-fertilizer increased P concentrations of corn root and shoot in the presence of the LDH-biochar and LDH-hydrochar but decreased the K concentration of root in biochar, LDH-biochar and no amendment treatments and had no significant effects on N and K concentrations in the shoot. The application of P-fertilizer decreased P translocation factor in presence of the LDH-biochar and LDH-hydrochar and had no significant effect on P translocation factor in all other treatments. Using P-fertilizer had no significant effect on K translocation factor in all treatments. Biochar, hydrochar, LDH, LDH-biochar, and LDH-hydrochar had no significant effects on P and K translocation factors. The translocation factor of P was greater than 1 in all treatments, except for the LDH-biochar-P and LDH-hydrochar-P treatments. Also, the translocation factor of K was greater than that of P in all treatments. Due to the structural similarities between biochar and hydrochar, LDH-biochar and LDH-hydrochar, and LDH-biochar-P and LDH-hydrochar-P, the root and shoot dry matter and concentrations of the studied elements in corn root and shoot were not significantly different between the biochar and hydrochar, LDH-biochar and LDH-hydrochar, and LDH-biochar-P and LDH-hydrochar-P treatments, respectively. P-fertilizer had synergistic relationships with biochar, hydrochar, LDH-biochar, and LDH-hydrochar but antagonistic relationships with LDH, LDH-biochar-P, and LDH-hydrochar-P composites in terms of dry matter and P concentrations in corn root and shoot. So, applications of the biochar, hydrochar, LDH-biochar, and LDH-hydrochar accompanied by P-fertilizer and the use of LDH-biochar-P and LDH-hydrochar-P without the application of P-fertilizer can be proposed for corn cultivation under similar conditions.

Climate change caused by increasing atmospheric concentration of CO2 due to fossil fuel combustion and land use change is one of the biggest challenges facing our modern world. Being a persistent and carbon-rich solid material, biochar remains stable for hundreds or even thousands of years in the environment. It can, thus, store carbon to mitigate the effects of climate change and global warming. Addition of biochar to soil may also reduce, directly or indirectly, N2O and other greenhouse gases in soils. It is produced in a process called ‘pyrolysis’, which is indeed the thermal degradation of organic materials in environments with no oxygen or only a limited supply. During pyrolysis, biomass undergoes a variety of physical, chemical, and molecular changes in which it is converted into the three liquid (bio-oil), solid (biochar), and gas phases. All the three phases produced by pyrolysis can be used as fuel. Moreover, addition of biochar to soil not only leads to carbon sequestrationbut also improves soil physical, chemical, and biological properties, thereby playing an important role in sustainable agriculture and soil management by improving soil fertility and plant yield.

Biochar is a carbon-rich organic material that is produced from the pyrolysis of organic matter under low or no oxygen. The unique physical and chemical properties of biochar distinguish it from other soil organic matter. Addition of biochar to soil can improve not only its physical properties such as specific surface area, water holding capacity, aeration, and resistance to soil erosion but also its chemical properties such as cation exchange capacity, pH, organic carbon, nutrient availability, and reduced risk of soil contaminants. Moreover, it has such advantageous biological effects as increasing microorganism colonies and their protection against predators, raising soil fertility, enhancing crop yield and carbon sequestration, climate change mitigation, and biofuel production. However, due to its novelty, its positive and negative effects on the environment and interactions with various soil components are not clearly known. In addition, biochar properties may change over time and nothing is yet known about these changes and their long-term effects. Despite the universal attention shown to biochar for its expected beneficial effects on soil and carbon sequestration, few studies have as of yet been devoted to its production and application in Iran, which warrants studies to be conducted on biochar production and application to Iranian soils.

Environmental risk of heavy metals is associated with the changes of their chemical forms and bioavailability in soil. Therefore, distribution of metals in chemical forms in soil need to be more studied. To investigate the effects of alfalfa green manure (2% w/w) and root activity on chemical forms of lead, zinc, copper and nickel in a lead-zinc contaminated soil, a greenhouse experiment was conducted using rhizobox systems in a split plot design, with 3 replications, two levels of green manure (0 and 2%) and 4 zone by distance from root. Sequential extraction procedure (Tessier) was also carried out to differentiate the chemical forms of heavy metals in the soil samples. Results showed that the green manure addition enhanced dissolved organic carbon concentration (DOC) and reduced pH of the soil. It also increased exchangeable, organic matter-bound fractions and bioavailability of the metals. The highest and lowest values of DOC were found in rhizosphere and bulk soil respectively. The pH value in the rhizosphere was 0.4 times lower than in the bulk soil. Oxide fraction of metals increased with distance from the root that maybe related to the change of oxide fraction to other forms. Addition of green manure to the soil increased oxide fraction and bioavailability of lead in the rhizosphere that maybe approve the change of oxide form to more bioavailable forms. The results of plant analysis showed that green manure addition reduced the concentration of lead, zinc and copper and also reduced the uptake of lead and copper in shoots of corn.

Heavy metals behavior in soil is complicated due to their different chemical forms. To investigate the effects of single and mixed rhizosphere of canola and corn on chemical forms and DTPA extractability of zinc, this experiment is set up using a rhizobox system. The rhizoboxes divided into four different parts and canola and corn were seeded in the middle part mixed or separately. The plants were harvested after the growth period and the soil samples were taken from different parts of the rhizoboxes. The results showed that, due to the decrease in pH and increase in dissolved organic carbon, the distribution of different forms of zinc changed in rhizosphere as compared to the bulk soil. The DTPA extractability of Zn is increased in the rhizosphere, while decreased with distance from the root. The soil pH increased and the DOC decreased from rhizosphere toward the bulk soil while the exchangeable, organic bound and oxide forms of zinc changed differently. There was a positive correlation between DOC and DTPA extractable, exchangeable, and organic and carbonate bound forms of zinc while the correlation between these forms and soil pH and oxide bound Zn was negative. Zinc concentrations in corn and canola shoot decreased while zinc uptake increased over corn in mixed culture. The Zn transport factor from root to shoot in mixed culture was greater than corn but lower than canola in single culture.