Plant Nutrition, Soil Fertility and Fertilizers
Sepideh Raeisi; Nafiseh Rangzan; Naeimeh Enayatizamir
Abstract
Introduction: Zinc (Zn) is a vital nutrient for plants, needed in small amounts for their reproductive and physiological functions. Zinc deficiency is common in soils with high pH, low organic matter, and high calcium carbonate. Soil salinity is one of the most important and common environmental stresses ...
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Introduction: Zinc (Zn) is a vital nutrient for plants, needed in small amounts for their reproductive and physiological functions. Zinc deficiency is common in soils with high pH, low organic matter, and high calcium carbonate. Soil salinity is one of the most important and common environmental stresses in the world. The impact of salinity on the forms of zinc and its availability in soil has varied. Among the chemical forms of zinc, the soluble and exchangeable forms have the highest mobility and availability for plants; whereas the residual form, associated with the crystalline lattice of soil minerals, appears to be very inactive. Depending on the physical and chemical properties of the soil, the carbonate forms, those bound to iron and manganese oxides, and the organic forms of elements are relatively active and have the potential to be available for plants. Organic materials like carbon black can alter zinc distribution. Zinc-solubilizing bacteria enhance zinc availability by converting insoluble forms into absorbable ones. This study examines the effects of carbon black and growth-promoting bacteria on zinc forms and soil properties under varying salinity levels.Materials and Methods: In this study, to investigate the effect of carbon black and inoculation of a mixture of two bacteria on the distribution of chemical forms of zinc under salinity stress, a pot experiment with four replications was conducted as factorial with three factors: salinity (2, 5, and 8 dS m-1), carbon black (0, 4% by weight), and a mixture of two bacteria (inoculated and non-inoculated). The bacteria included Enterobacter cloacae and Bacillus sp., which were obtained from the microbial collection of the Soil Science Department at Shahid Chamran University of Ahvaz. The experiment was carried out in a completely randomized design in 2023 in the greenhouse of Khuzestan Agricultural Sciences and Natural Resources University. In 5-kilogram pots, 10 corn seeds were planted, which were reduced to 6 plants per pot after ensuring germination. Two months after planting, soil samples were taken from the pots, and after removing the roots and passing through a 2-millimeter sieve, they were transferred to the laboratory to determine the chemical forms of zinc. The sequential extraction method was used to determine the chemical forms of zinc. The fractions—exchangeable, carbonate, iron and manganese oxides, organic, and residual—were determined. The concentration of zinc in the extracts obtained from the various stages of sequential extraction of the soil was read using an atomic absorption device. Some biological properties of soil, such as microbial biomass carbon via fumigation-extraction method, catalase activity via the titration method, and soil respiration by titration of residual NaOH, were measured.Results and Discussion: The interaction effect of carbon black× inoculation× salinity on chemical forms of Zn was significant. The results showed that the inoculation of a mixture of two bacteria and addition of carbon black in soil significantly increased the soluble and exchangeable, carbonate, iron and manganese oxide, and organic forms of zinc. Inoculation of a mixture of two bacteria and carbon black to the soil at a salinity level of 2 dSm-1 resulted in an increase in EXCH-zinc from 1.02 to 1.38 mgkg-1 compared to the control, which is equivalent to a 35% increase. Inoculation of the bacterial mixture and the addition of carbon black to the soil increased all forms of zinc except the residual form. With increasing salinity level, the amounts of soluble and exchangeable, carbonate-bound, and oxide-bound forms increased, while the organic-bound form decreased. The highest amounts of microbial biomass carbon, catalase activity, and soil respiration were measured in the treatment with bacteria, carbon black, and at a salinity level of 2 dS m-1, with values of 19.9 mg-Cmic 100g-1, 0.95 mLKMnO4g-1h-1, and 70.2 mgCO2 100g-1day-1, respectively. There was a positive correlation between soil respiration and all forms of zinc, except the residual form, but the correlation between soil respiration and the residual form of zinc was negative, indicating the influence of microbial activity on different forms of zinc.Conclusion: The addition of a carbon black to the soil and inoculation of a mixture of two bacteria caused zinc to convert from residual form to soluble and exchangeable, carbonate, oxide, and organic forms, increasing the availability of zinc in accessible fractions at various salinity levels. Overall, zinc-solubilizing bacteria offer a promising solution for enhancing zinc availability in saline soils, promoting plant health, and contributing to sustainable agricultural practices.
Soil Biology, Biochemistry and Biotechnology
Elham Sadeghi; REZA GHORBANINASRABADI; Seyed Ali Reza Movahedi Naini; Mojtaba Barani Motlagh; Mostafa Khoshhal Sarmast; Mohammad Reza Pahlevan Rad
Abstract
Introduction: Plant growth and crop productivity may be adversely affected under unfavorable environmental conditions, such as a lack of organic matter in the soil. To counteract the negative impacts of these challenges, a unique strategy is required. The paucity of organic inputs, which is common in ...
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Introduction: Plant growth and crop productivity may be adversely affected under unfavorable environmental conditions, such as a lack of organic matter in the soil. To counteract the negative impacts of these challenges, a unique strategy is required. The paucity of organic inputs, which is common in conventional agricultural production, can lead to soil degradation, erosion, and loss of soil organic matter, which are unfortunate consequences. Soil organic amendments have been shown to have beneficial effects on crop production and a wide range of soil properties in agricultural systems. However, the limited availability of phosphorus (P) in soil can significantly restrict crop growth and productivity, particularly in maize crops. Adequate P supply has been found to enhance early maturity, crop quality, and yield. However, the prolonged use of chemical fertilizers such as NPK has been found to have adverse effects on soil fertility and crop quality. As a result, the combined application of organic and chemical fertilizers has been proposed as an effective approach compared to the single application of organic or chemical fertilizer alone. Therefore, this study aimed to assess the potential benefits of using compost and Triple Super Phosphate fertilizer (TSP) application on the chemical and biological properties of soil, as well as the properties of forage maize (cv. SC704), in loess soil.Materials and Methods: A factorial experiment was conducted using a completely randomized design with three replications. A total of 36 samples were performed in two separate cultivated and incubated experiments. A pot experiment was conducted to invwstigate the effects of simple and enriched compost, containing urea and Streptomyces, and varying amounts of TSP fertilizer (0, 10, 40, and 100 mg/kg), on soil properties and maize plant growth. In addition, an incubation experiment was conducted to measure the effects of the same treatments on soil microbial biomass and activity. The effect of treatments were analyzed as factorial under a completely randomized design. The biomass of maize plants was measured at the time of harvesting (the time from planting to harvesting of forage maize was 80 days). Some parameters such as available phosphorus, substrate-induced respiration, microbial biomass carbon, and some enzyme activity (acid phosphatase, alkaline phosphatase, catalase and urease) were measured in soil.Results and Discussion: The findings of this study indicated that the application of compost and TSP fertilizer had significant effects on plant biomass. Specifically, compost application led to an increase in microbial biomass carbon and enzymes activity (acid phosphatase, alkaline phosphatase, catalase and urease) in the soil, ultimately promoting plant growth. Moreover, the combined application of compost and TSP fertilizer increased the availability of phosphorus, substrate-induced respiration, and microbial biomass carbon in the soil. Based on the findings, the combined application of TSP and compost resulted in further increases in substrate-induced respiration (63-168%), microbial biomass carbon (72-167%), available phosphorus (29-103%), and enzyme activity (acid phosphatase (4-21), alkaline phosphatase (14-34%), catalase (13-32%), and urease(54-159%)) compared to the application of each amendment alone. This suggests that the addition of both TSP and compost promotes the availability of easily accessible nutrients for microbial growth and soil enzymes (acid phosphatase, alkaline phosphatase, catalase and urease) activity. The highest amount of available phosphorus, microbial biomass carbon, substrate-induced respiration, catalase activity and urease activity in cultivated soil (23%, 270%, 93%, 68%, 1.8%, respectively) and incubated soil (18%, 243%, 90%, 53%, 1.2%, respectively) were observed in C2P3 treatment. The results also indicated that the enriched compost+TSP treatment led to the highest substrate-induced respiration and microbial biomass carbon, followed by simple compost+TSP, enriched compost only, simple compost only, TSP fertilizer only, and the control. The increase in enzyme activity (P<0.01, r=0.90), and available phosphorus (P<0.01, r=0.60) in the soil positively influenced plant growth. Specifically, the simultaneous application of compost and TSP had a greater effect on maize plant biomass. The highest root biomass (2.80 g), stem biomass (10.4 g), and leaf biomass (2.27 g) were observed in the enriched compost and 100 mg kg-1 TSP treatment, which differed significantly from the other treatments.Conclusion: The results of this study demonstrated that the addition of compost and TSP to loess soils can promote microbial biomass carbon, substrate-induced respiration, enzyme activity (acid phosphatase, alkaline phosphatase, catalase, and urease), available phosphorus, and maize plant growth. Moreover, the use of compost can protect soil microbial and enzymatic activities in loess soils. Thus, the simultaneous application of enriched compost with TSP can reduce the use of chemical fertilizers and their negative environmental impacts.
Elham Sadeghi; REZA GHORBANINASRABADI
Abstract
Introduction: Soil microorganisms play an important role in maintaining soil quality through the decomposition of organic matter and nutrients cycling. The quantity of plant residue has a positive effect on the accumulation of organic carbon in the soil. One of the most important problems hampering the ...
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Introduction: Soil microorganisms play an important role in maintaining soil quality through the decomposition of organic matter and nutrients cycling. The quantity of plant residue has a positive effect on the accumulation of organic carbon in the soil. One of the most important problems hampering the release of nutrients from plant residues is the high content of lignocellulose in their structure. Therefore, biological treatment has been considered as a candidate to improve lignocellulosic conversion and more release of nutrients from them. Salinity reduces microbial biomass and decreases their activity in decomposition of soil organic matter and organic matter input into soil. Due to the importance of the role of microorganisms in the storage and release of energy and nutrients in the soil, in recent years, increasing attention has been paid to the estimation of microbial activity and biomass in soil. Therefore, the aim of this study was to study the effect of salinity, inoculation of Pleurotus astreatus and wheat residue on respiration, microbial biomass carbon, organic carbon, carbon availability index and metabolic quotient.Materials and Methods: The experiment was conducted as a completely randomized design with factorial arrangement in three replications under controlled laboratory conditions at Gorgan University of Agricultural Sciences and Natural Resources. Factors included three salinity levels (0, 8 and 15 dS m-1), two fungal levels (0 and 5%) and two wheat residue levels (0 and 1%, w/w). Salinity treatments including (control), 8 and 15 dS m-1 was applied using a mixture of salts (NaCl, KCl and MgCl2 with a molar ratio of 3:2:1). Wheat straw was treated pleurotus fungus and the treated straw was then thoroughly mixed into the soil. To activate the microbial population, soil moisture was adjusted to about 70% of the field capacity and the containers were pre-incubated at room temperature for 2 weeks. The samples were incubated at 25±2°C for 90 days. Microbial biomass carbon, organic carbon was measured at monthly intervals, microbial respiration was measured weekly and substrate-induced respiration (SIR) was measured once at the end of the incubation period.Results and Discussion: The results show that salinity has a negative effect on microbial activity and population, but wheat residues reduce the effect of salinity stress on soil microbial community. Inoculation of Pleurotus into the soil also increased the respiration and microbial biomass. The interaction of wheat residues and Pleurotus on microbial activity in saline soil was greater than their effect alone. According to the results, the simultaneous addition of Pleurotus and wheat residue increases organic carbon (%98), microbial respiration rate (90%), substrate respiration (69%) and microbial biomass carbon (79%) and decreases the metabolic coefficient (6%). Salinity reduced respiration (78%), microbial biomass carbon (81%) and carbon availability index (23%), which indicates a decrease in carbon for microbial activity in saline soils. The lowest and highest microbial activity and biomass were in saline soil (15 dS m-1) not treated with wheat residues and Pleurotus (S2F0R0) and in non-saline soils treated with wheat residues enriched with Pleurotus (S0F1R1), respectively. The results showed that higher salinity level (15 dS m-1) further decreased the measured characteristics including carbon availability index, respiration and microbial biomass carbon compared with 8 dS m-1 salinity level in all treatments. In non-treated soil with wheat residue and Pleurotus, salinity level of 8 dS m-1 reduced MBC by 43, 46 and 44 % compared to control (non-saline) soil. The results showed that there was a significant negative correlation between microbial respiration rate and salinity (P <0.01, r = - 0.87). Salinity reduced microbial respiration rate and the effect of salinity on reducing microbial respiration rate of soil with EC 15 dSm-1 was higher than lower salinity level (8 dSm-1). Also, inoculation of Pleurotus in soil led to increase microbial respiration rate compared with non-treated one. According to the results, salinity levels of 8 and 15 dSm-1 reduced carbon availability index in soil treated with Pleurotus and wheat residue by 18% and 23%, respectively, compared to non-saline soil.Conclusion: The addition of wheat straw enriched with Pleurotus astreatus increased microbial respiration, organic carbon, microbial biomass carbon, substrate-induced respiration and carbon availability index due to the increase of available substrate. Therefore, in saline soils with carbon restriction, increasing the level of organic matter, increased microbial activity and biological potentials in the soil. However, further information on responses of microbial indicators to the joint effect of salinity and Plant residues enriched with other microorganisms is required.ReceivedReceived in revised formAcceptedKey words:Carbon availability index, Microbial biomass carbon, Microbial respiration rate, Soil organic carbon, Substrate-induced respiration
