Sulfur deficiency arising due to intensive cultivation, use of sulfur free fertilizers and reduction in atmospheric sulfur depositions has become a major issue limiting crop production in many parts of the world. Elemental sulfur could be a good source of available S, but its slow oxidation is a problem for its efficient use as a sulfur fertilizer. Main objective of the study was to assess the effect of organic amendments (OA) and elemental sulfur (ES) on microbial activities, sulfur oxidation and availability in soil. A laboratory incubation experiment was carried out for a 56 days period using two sulfur deficient alkaline soils. Organic amendments (OA), i.e., farmyard manure (FYM), poultry litter (PL) and sugarcane filter cake (SF), were applied (1% w/w) with or without elemental sulfur (ES) at 50 mg kg−1. Application of ES alone or in combination with OA significantly increasedCO2-C evolution, microbial biomass, and enzyme activities in the soils, except dehydrogenase activity (DHA) which was not affected by ES application. Combined application of OA and ES had a more pronounced effect on microbial parameters compared to ES or OA applied alone. Ratios of dehydrogenase activity-to-microbial biomass C and arylsulfatase activity-to-microbial biomass C were high in ES+FYM and ES+SF treatments, respectively. Elemental sulfur got sufficiently oxidized resulting in significant improvement in plant available S. Relatively more ES was distributed into C-bonded-S than ester bonded-S. Increase in sulfur availability in ES+OA amended soils was the combined function of sulfur oxidation and mineralization processes through improved microbial activity.

Continuous application of phosphate (P) mineral to soil renders apatite addition during each crop growing season which is of great concern from a sustainable agriculture viewpoint. Use of efficient phosphate solubilizing microbes (PSB) is one of the most effective ways to solubilize this apatite mineral in the soil. The current study targeted hydroxyapatite mines to explore, isolate and characterize efficient P solubilizers to solubilize apatite in the soil. Efficiency of isolated microbes to solubilize rock phosphate (hydroxyapatite) and tri-calcium phosphate (TCP) as well as indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate deaminase (ACC) activity were tested. Identification and phylogenetic analysis of bacterial and fungal isolates were carried out by 16S rRNA and internal transcribed spacer (ITS) rDNA sequence analyses, respectively. The isolated bacterial strains were identified as Staphylococcus sp., Bacillus firmus, Bacillus safensis, and Bacillus licheniformis whereas fungal isolates were identified as Penicillium sp. and Penicillium oxalicum. Results showed that the impact of identified strains in combination with three phosphate fertilizers sources (compost, rock phosphate and diammonium phosphate (DAP)) was conspicuous on maize crop grown in pot. Both bacterial and fungal strains increased the P uptake by plants as well as recorded with higher available P in post-harvested soil. Penicillium sp. in combination with compost resulted in maximum P-uptake by plants and post-harvest soil P contents, compared to other combinations of P sources and bio-inoculants. Screening and application of efficient P solubilizers can be a better option to utilize the indigenous phosphate reserves of soil as well as organic amendments for sustainable agriculture.

Due to the scarcity of water, raw sewage effluents are often used to irrigate arable suburban soils in developing countries, which causes soil contamination with toxic metals. Soil microorganisms involved in biochemical transformations are sensitive to heavy metals contamination. The study was designed to investigate the effect of organic amendments on the microbial activity of cadmium (Cd), lead (Pb) and zinc (Zn) fractions and their bioavailability in soils contaminated with wastewater irrigation. Three metal contaminated soils under wastewater irrigation were collected, ground, sieved and added to incubation jars. Two organic amendments: wheat straw and chickpea straw, were applied (1% w/w) to the soil before incubation for 84 days at 25 °C. The CO2-C evolution after 1, 2, 3, 5, 7, 10 and 14 days was measured and thereafter was also measured weekly. Soil samples collected at 0, 14, 28, 42, 56, 70 and 84 days after incubation were analyzed for microbial biomass carbon (MBC). Sequential extraction for metal fractionation of samples was carried out collected at 0, 28, 56 and 84 days. Three soils differed significantly in evolved MBC and ∑CO2-C. Chickpea straw addition significantly increased soil MBC as compared to the wheat straw. Organic amendments significantly increased ∑CO2-C evolution from the soils, which was higher from chickpea straw. The addition of crop residues did not affect total Pb, Cd and Zn contents in soils. The concentration of exchangeable, carbonate bound and residual fractions of Pb, Cd and Zn decreased (6–27%), while the organic matter bound fraction increased (4–75%) with straw addition. Overall, the organic amendments improved microbial activity and reduce the bioavailability of toxic metals in wastewater irrigated soils. Furthermore, organic amendments not only reduce economic losses as they are cheap to produce but also minimize human health risks from heavy metals by hindering their entry into the food chain.

Environmentally hazardous wastewaters from various origins could prove an impending source for phosphorus (P) recovery as struvite. This study aimed to employ an eco-friendly approach for P utilization from struvite, and to neutralize its alkaline effect in the soil through supplementation of sulfur-oxidizing bacteria (SOB) Acidithiobacillus thiooxidans IW16. Struvite precipitated and recovered from wastewater was tested for P release and bioavailability to grow wheat in alkaline soil under greenhouse conditions. Treatments were control (no P application), P from single superphosphate (SSP) fertilizer, P from struvite, P from struvite + sulfur (100 mg kg −1 of soil), and P from rock phosphate; and all these treatments were compared with and without SOB inoculation through irrigation water. Struvite application, especially with sulfur and/or SOB, maintained an adequate P level (as with SSP fertilizer) in both wheat plants and soil throughout the growing period. Wheat plant agronomic attributes were also improved with struvite as for SSP fertilization. Moreover, supplementation of SOB inoculum with struvite and other P sources significantly improved the P bioavailability and crop yield through increased phosphate solubility in alkaline soil. In conclusion, inoculation of SOB especially with sulfur (S) supplementation in struvite treatment caused the pH reduction of alkaline soil through S oxidation (H 2 SO 4 formation), which solubilized the fixed-P in struvite as well as soil and thus improved P bioavailability to wheat plants. These findings strengthen the concept of struvite scavenging from wastewater for environmental safety, and to introduce it as an alternative resource for P fertilization.

Sulfur availability depends upon the distribution of S forms in soil, interaction among them, and soil microbial properties. Organic amendments play a vital role in maintaining adequate S reserves in soil. However, two important questions in this regard are (i) the effect of microbial activity on sulfur oxidation in soil, and (ii) the relationship of sulfur fractions to available S pool in soil. The present experiment was designed to assess the effect of organic amendments on sulfur fractions, availability, and microbial properties in soil. Two alkaline subtropical soils belonging to Missa (silt loam Typic Ustochrept) and Kahuta (sandy loam Udic Haplustalf) soil series were amended with organic amendments, viz. farmyard manure (FYM), poultry litter (PL), and sugarcane filter cake (SF), at 1% w/w and incubated at 25°C for 56 days maintaining soil moisture at 50% WHC. CO 2-C evolution rate, the ∑CO 2-C, and also the ∑CO 2-C to microbial biomass C differed with the soils and were higher in poultry litteramended soils. Dissolved organic C (DOC), microbial biomass C (MBC), and dehydrogenase activity (DHA) were also higher in poultry litter while the microbial biomass S (MBS) and arylsulfatase activity (ASA) were higher in the sugarcane filter cakeamended soils. Organic amendments significantly increased plant-available SO 4 2− and enhanced C-bonded S, and inorganic S fractions in the following order: sugarcane filter cake > poultry litter > farmyard manure. Organic amendments significantly improved microbial activity and S availability in soil depending upon their labile organic C, organic S, and available S contents.