Occurrence of Sphingomonas olei with elemental S oxidation capability in sodic soil: Potential role in sodicity reclamation and plant growth promotion

The success of the sodic soil reclamation using elemental S (S°) depends on the population of the native S° oxidizers. Augmenting the native flora of the sodic soils with effective S° oxidizers can enhance the success of the sodic soil reclamation. Present study reports for the first time the S° oxidation potential of the Sphingomonas olei strain 20UP7 isolated from sodic soils with pHs 9.8 and ECe 3.6 dS m-1. Inoculation with S. olei strain 20UP7 caused 13.0-24.2 % increase in S° oxidation in different sodic soils (pHs 9.1-10.5). It improved the concentration of the Ca2+, Mg2+, PO43- and declined the HCO3- and total alkalinity of the soil solution. This isolate also showed appreciable P and Zn solubilization, indole acetic acid, ammonia, and titratable acidity production in the growth media. It tended to the formation of biofilm around sulphur particles. The PCR amplification with gene-specific primers showed the occurrence of soxA, soxB, and soxY genes with a single band corresponding to length of 850, 460, and 360 base pairs, respectively. The integration of the S. olei strain 20UP7 with S° caused 21.7-25.4 % increase in the rice and wheat yield compared to the soil treated with S° alone. This study concludes that the S. olei, native to high saline-sodic soils can be utilized for improving the sodicity reclamation and plant growth promotion using elemental S based formulations.

Characterization of flue gas desulphurized (FGD) gypsum of a coal-fired plant and its relevant risk of associated potential toxic elements in sodic soil reclamation

Thermal Power Plant generates FGD gypsum as by-product during coal combustion. This study evaluates the characterization (spectroscopic and elemental), potentially toxic elements (PTEs) distribution, and environmental risk assessment of FGD gypsum for safe and sustainable use in agriculture. The XRD and SEM analysis confirmed the dominance of crystalline CaSO4·2H2O in FGD gypsum. The order of concentrations of PTEs in FGD gypsum was Fe > Al > Mn > Zn > Ni > Co. The residual fraction was the dominant pool, sharing 80-90% of the total PTEs. The heavy metals (HMs) were below the toxic range in the leachates. The Co, Ni, Al, Fe Mn, Zn had low (< 10%) risk assessment code and the ecotoxicity was in the range of 0.0-7.46%. The contamination factor was also low (0.0-0.16) at the normal recommended doses of FGD gypsum application for sodicity reclamation. The enrichment factor was in the order of Al < Mn < Co < Zn < Ni. Mn [enrichment factor (Ef) 1.2-2.0] and Co (Ef 1.7-2.8) showed negligible enrichment of metals, whereas Ni (Ef 4.3-5.2) and Zn (Ef 4.5-5.6) reported moderate accumulation in soil. The application of FGD gypsum @ 10 t ha-1 for sodicity reclamation will develop a geo-accumulation index below the critical values indicating its safe and sustainable use to achieve land degradation neutrality (LDN) and UN's Sustainable Development Goals.

Characterization and ecotoxicological risk assessment of sewage sludge from industrial and non-industrial cities

The present study highlights the occurrence and the temporal variations of physicochemical properties, and heavy metals in the sludge from sewage treatment plants (STPs) located in industrial (two sites) and non-industrial (one site) cities of Haryana, India. The sludge was acidic (5.59) to neutral (7.21) with a mean EC of 7.4 dS m-1. Prominent heavy metals present in the sewage sludge from industrial sites were Cd, Ni, and Cr with maximum values of 2.83, 1449.0, and 3918.5 mg kg-1, respectively. The contamination and enrichment factor better explained the buildup of Ni, Cr, and Cu in the sewage sludge from industrial sites. The pH, total carbon, phosphorus, and other water-soluble anions, viz. SO42-, Cl-, HCO3-, and PO43-, were the most important attributes of sludge controlling the binding and removal of the metals with particulate matters during the phase separation in STPs. These attributes explained about 90% of the variation in Cd, Ni, Cr, Cu, Mn, and Zn content of the sludge from different STPs. Sludge from the non-industrial site had a low potential ecological risk index of 74.0 compared to a very high-risk index of 2186.5 associated with the industrial sites. This study concludes that besides the concentration of the heavy metals, the enrichment factor coupled with geo-accumulation or ecological risk index can effectively categorize the sludge. However, these indices need to be linked with bioaccumulation, bioaccessibility, and biomass quality under different agroecologies for guiding the safer use of sewage sludge in agriculture.

Irrigation water quality, gypsum, and city waste compost addition affect P dynamics in saline-sodic soils

The amendments used for sodicity reclamation also profoundly influence P dynamics and leaching losses. This study characterized the effect of irrigation water quality on P dynamics and leaching from saline-sodic soil during reclamation utilizing gypsum alone or in combination with manure and city compost. Changes in properties of unleached and leached soils were fitted with labile P pools using redundancy analysis. The relation between leachate properties and P loss was explained by means of monitoring leachate properties up to ten pore volumes. During incubation, the water-extractable P (P_H2O) concentration was greater than Olsen's P (P_NaHCO3) in all treatments. The P_NaHCO3 decreased in proportion to the amount of gypsum applied. Applying the organics with gypsum increased the P_NaHCO3, P_H2O, and organic P concentration compared to gypsum alone. The labile P pools in soil were positively correlated with HCO₃^- content (r = 0.39-0.77; P < 0.05) of leached and unleached soils. Adding gypsum and compost caused a 10-14% decrease in cumulative P leaching. The cumulative P leaching were greater with rainwater compared to saline water of SAR (sodium adsorption ratio) 5 and 15. The CO₃^2-, HCO₃^-, pH, and SO₄^2-content of the leachate explained about 71% variability in total P leaching (adj. R² = 0.71; P < 0.001). This study concludes that low electrolyte water had a greater risk of P leaching and associated environmental pollution. Leaching of the saline-sodic soil amended with gypsum and city waste compost with low SAR saline water can reduce P leaching compared to good quality rainwater.

Changes in soil microbial biomass and organic C pools improve the sustainability of perennial grass and legume system under organic nutrient management

Introduction

The perennial grass-legume cropping system benefits soil because of its high biomass turnover, cover cropping nature, and different foraging behaviors. We investigated the response of soil organic carbon (SOC) pools and their stock to organic and inorganic nutrient management in the Guinea grass and legume (cowpea-Egyptian clover) cropping system.

Methods

Depth-wise soil samples were collected after harvesting the Egyptian clover. Based on the ease of oxidation with chromic acid, different pools of SOC oxidizable using the Walkley-Black C method, very labile, labile, less labile, non-labile; and dissolved organic C (DOC), microbial biomass C (MBC), and total organic C (TOC) in soils were analyzed for computing several indices of SOC.

Result and discussion

After 10 years of crop cycles, FYM and NPKF nutrient management recorded greater DOC, MBC, SOC stocks, and C sequestration than the NPK. Stocks of all SOC pools and carbon management index (CMI) decreased with soil depth. A significant improvement in CMI, stratification ratio, sensitivity indices, and sustainable yield index was observed under FYM and NPKF. This grass-legume intercropping system maintained a positive carbon balance sequestered at about 0.8Mg C ha^-1 after 10 years without any external input. Approximately 44-51% of the applied carbon through manure was stabilized with SOC under this cropping system. The DOC, MBC, and SOC in passive pools were identified for predicting dry fodder yield. This study concludes that the application of organics in the perennial grass-legume inter cropping system can maintain long-term sustainability, enhance the C sequestration, and offset the carbon footprint of the farm enterprises.

Deficit saline water irrigation under reduced tillage and residue mulch improves soil health in sorghum-wheat cropping system in semi-arid region

Judicious application of saline water except for critical growth stages, could be the only practical solution to meet the crop water demand in arid and semi-arid regions, due to limited access to freshwater, especially during dry winter months. A field experiment was conducted to study the effect of tillage [conventional (CT), reduced (RT), and zero (ZT)], rice straw mulch and deficit saline-water irrigation in wheat (100, 80 and 60% of wheat water requirement, CWR) followed by rainfed sorghum on soil properties and the yields of the cropping system. Yields of both the crops were comparable between RT and CT, but the wheat yield was reduced in ZT. The RT, mulching and deficit saline irrigation in wheat season (60% CWR) increased the sorghum fodder yield. Olsen’s P (8.7–20.6%) and NH₄OAc-K (2.5–7.5%) increased in RT and ZT, respectively, over CT under both the crops. Deficit irrigation reduced soil salinity (EC_e) by 0.73–1.19 dS m⁻¹ after each crop cycle, while soil microbial biomass C (MBC) and N (MBN), dehydrogenase, urease and alkaline phosphatase reduced with an increase in EC_e. The α-glucosidase, MBC, EC_e, KMnO₄oxidizable N, and urease were identified as major contributors in developing the soil health index. Deficit irrigation (60% CWR) and rice straw mulching under ZT and RT showed higher values of soil health index. Overall, deficit saline-water irrigation under reduced tillage and straw mulching had the greatest potential in maintaining soil health, saving fresh irrigation water without affecting the productivity of the sorghum-wheat system in the semi-arid regions of India. Results also demonstrated that salt affected areas of arid and semiarid countries can replicate the protocol for indexing and screening of soil health indicators to assess the sustainability of a cropping system. This integrated management based on the nature of the available resources also provided a practical approach to achieve the target of land degradation neutrality and land restoration.