Roghayeh Vahedi; Mirhasan Rasouli-Sadaghiani; mohsen barin
Abstract
Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds ...
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Introduction: Trees pruning wastes by turning into compost and adding to soil improves the physical, chemical and biological properties of the soil. Soil biological indices are important aspects of soil quality, so soil quality is measured using different biological properties. The organic compounds are regularly released from plants into the rhizosphere, which increase the activity of the soil microbial community and improve the health of the soil. The organic matter such as compost, stimulates microbial activity like the enzymatic activity and microbial biomass in the soil. Another method to improve soil quality is the use of the microorganisms potential. The arbuscular mycorrhizal fungi (AMF) in soil can stimulate and increase soil microbial activity and also improve the activity of enzymes and microbial biomass in soil. The application of microorganisms and the addition of the organic matter to the rhizosphere can change the microbial communication composition of the rhizosphere. The Limiting roots to investigate the biological and chemical changes and the extent of these properties in the rhizosphere are challenges that have been less addressed. The rhizobox is one of the used tools to study the rhizosphere changes. The main objective of the present study was to investigate the effects of the compost prepared from pruning wastes of apples and grapes trees and also pruning wastes of apples and grapes trees on soil quality, in the presence of arbuscular mycorrhizal fungi, in rhizosphere of the wheat under the rhizobox conditions.
Materials and Methods; The present study was carried out in a completely randomized factorial design with three replications in rhizobox under greenhouse condition. The factors included the organic matter (compost of trees pruning wastes, trees pruning wastes and control) and soil (the rhizosphere and non-rhizosphere soil) in mycorrhizal inoculation conditions. The soil sample with light texture and low available phosphorus was prepared. The pruning wastes of apple and grape trees were collected from urmia orchards. Also, the compost of trees pruning wastes was prepared from the research greenhouse of Urmia University. The compost and pruning wastes were ground and crushed and then passed through a 0.5 mm sieve for the greenhouse experiment. The plants were planted in the rhizobox with the dimensions of 20 × 15 × 20 cm (length × width × height). The compost and pruning wastes were added to the boxes based on 1.5% pure organic carbon (each box contained 5.799 kg of soil). Glomus fasciulatum as mycorrhizal inoculation was used. The control treatments contained sterile soil with mycorrhizal inoculation and without organic matter. The wheat seeds (Triticumae stivum L.) of Pishtaz cultivar were grown in rhizoboxes. At the end of the growth period, organic carbon (OC) by Walkley-Black method, microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP) by fumigation extraction method, metabolic quotient index (qCO2) (microbial respiration per unit of biomass), microbial quotient index (microbial biomass carbon per unit of organic carbon), carbon availability index (CAI) (substrate-induced respiration/microbial biomass ratio), colonization Percentage of arbuscular mycorrhizal fungi, and acid (ACP) and alkaline (ALP) phosphomonoesterase enzymes activities by spectrophotometry method, were determined.
Results and Discussion: The results showed that the application of compost significantly increased organic carbon, microbial biomass carbon, microbial biomass phosphorus and decreased MBC/MBP compared with the control treatment. Furthermore, compost increased the organic carbon, microbial biomass carbon and microbial biomass phosphorus in the rhizosphere soil by 8.08, 45.79 and 37.18 % compared with the non-rhizosphere soil, respectively. The pruning wastes increased 1.45, 1.26 and 1.30 fold metabolic quotient, carbon availability and acid phosphomonoesterase activity in the rhizosphere compared with non-rhizosphere soil, respectively.The highest activity of the alkaline phosphomonoesterase enzyme and the percentage of mycorrhizal root colonization were also related to pruning waste treatments in rhizosphere soils.
Conclusions: Different characteristics of the organic matter and the microbial inoculation led to an increase in the biological indices in the rhizosphere zone compared with non-rhizosphere soils. The application of organic matter in the soil, along with microbial inoculation, will accelerate the biological activity of the soil and thus contributes to a better cycle of nutrients in the soil. Following the application of organic matter, microorganisms rapidly grew and led to an increase in biological activity, such as increase activity of phosphomonoesterase enzymes, carbon and phosphorus of microbial biomass in the rhizosphere. It could be argued that increased activity of phosphomonoesterases and the microbial biomass and decreased metabolic quotient in the soil were influenced by the application of the organic materials and mycorrhizal inoculation. The findings of this study have a number of important implications for future practice. Therefore, the use of the organic materials and biological potential of the microorganisms are one of the most important tools to maintain organic carbon balance of the soil, contributing to the stimulation of soil microbiological activities.
faeze lotfi; amir fotovat; reza khorasani; Mahdi Bahraini
Abstract
Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical ...
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Introduction: The pollution of soils by heavy metals due to human activities poses a serious concern for human and environmental health. In order to evaluate the risks of heavy metal contamination such as cadmium in soil, it is necessary to understand its bioavailability which depends on its chemical forms in the soil. According to Tessier (1979), heavy metals can be found in various chemical forms in soil including exchangeable, bound to carbonates, bound to iron and manganese oxides and bound to organic matter and residual. These fractions significantly influence the cadmium mobility and bioavailability. Distribution of metals in chemical forms in soil depends on soil pH, amount of organic matter, oxidation-reduction potential and ionic strength. Root exudation, soil texture, cation exchangeable capacity and amount of calcium carbonate may also impact chemical forms of cadmium. Many studies have showed that plant root may affect the chemistry of heavy metals in soil root zone. The objective of this study was to evaluate the effect of organic matter on the distribution of cadmium in corn root media.
Materials and Methods: To investigate the effect of organic matter (cow manure) and root activity on chemical forms of cadmium, a greenhouse experiment was conducted using rhizobox. The contaminated soil sample used in the study was collected from Zanjan. This greenhouse experiment was conducted in a factorial design, with 2 replications, two levels of organic matter (0 and 1.5%) and three zones classified based on their distance from root. The soil samples were air dried and crushed to pass through a 2-mm sieve. The cultivation was conducted using a rhizobox. The rhizobox consisted of three parts: 1.central compartment (rhizosphere), 2.close to rhizosphere, and 3. soil bulk. Soil samples were mixed with fertilizer and packed in rhizobox. Eight pre-germinated maize seedlings were transferred to the central compartment and five days after germination, thinned to four plants. Ten weeks after planting, corn plants were harvested for analysis. The compartments of rhizobox were separated. The collected plant samples (root and shoot) were rinsed with deionized water and oven-dried at 70 °C. Soil samples were also measured for pH, CEC and total organic carbon. The chemical forms of cadmium in the soil and plant samples were identified by the sequential extraction procedure proposed by Tessier (1979). Bioavailable cadmium in soil was also extracted by DTPA-TEA.
Results and Discussion: Results showed that the highest amount of soil cadmium was found in carbonate fraction. Adding organic matter increased the soil pH, CEC and organic carbon amount, whereas none of chemical forms of cadmium were significantly affected by adding organic matter. Bioavailability of cadmium, however, decreased by adding organic matter to soil, It can be therefore concluded that increment in cadmium uptake due to increased organic matter led to decreased cadmium bioavailability. The exchangeable cadmium was negatively correlated to soil organic carbon, while bioavailable cadmium was negatively correlated to soil pH, CEC and amount of soil organic carbon. Moreover, our results indicated that the fractions of cadmium were not significantly affected by distance from the root. Moreover, adding organic matter insignificantly increased concentration of cadmium in shoots, roots and total plants.
Conclusion: In this study, among different chemical forms of cadmium, only bioavailable cadmium was significantly affected by adding organic matter to soil. Additionally, soil pH, CEC and organic carbon were significantly increased by adding organic matter. These results indicate that addition of organic matter to soil may indirectly influence chemical forms of cadmium through impacting soil properties (soil pH, CEC and organic carbon). The addition of organic matter had the most influence on carbonate fraction of cadmium which may be potentially available to plant. It seems that addition of organic matter (cow manure) may result in increase of cadmium concentration in plant. Therefore, it can be concluded that addition of cow manure to calcareous soils with neutral to slightly alkaline pH may lead to increased cadmium uptake by the plant (corn) and reduced soil cadmium concentration.
