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Higher pH of calcareous soils and mineral fertilizers lowers the bioavailability of plant nutrients. Hence, it requires amending the nature of nutrients input through suitable bioactive materials, like sulfur (S), organic, microbial, and nano-materials. This study assessed the effects of S-enriched composites of organo-phosphate (OP) and bio-organic phosphate (BOP) on soil and plant attributes. Elemental sulfur (ES) and nano-sulfur (NS) were admixed separately in compost and rock phosphate (RP) with/without sulfur-oxidizing bacteria (SOB), viz., Acidithiobacillus thiooxidans. Sulfur-based amalgams were incubated at 25–35 °C for 60 days to develop S-enriched organo-phosphate (ES-OP) and bio-organic phosphate (ES-BOP and NS-BOP) composites. Greenhouse and micro-plot experiments were conducted to evaluate the impact of these composites on nutrients bioavailability and vegetative growth of maize. Treatments included control (no sulfur), ES (12.5 kg ha−1), ES-OP (50 kg ha−1), ES-BOP (50 kg ha−1), and NS-BOP (50 kg ha−1) application in soil. Inoculation with SOB in both ES-BOP and NS-BOP reduced the pH and increased macronutrients as compared to ES-OP. Thus, ES-BOP and NS-BOP improved maize growth and soil nutrients status. Composite NS-BOP rendered the highest N, P, K, and S concentrations in both soil and plants due to lower soil pH. Application of S-BOP containing Acidithiobacillus thiooxidans, and use of nano-S are beneficial for improving nutrients bioavailability and plant growth in calcareous soils via pH reduction. These composites are low-cost, nutrients-rich, and have greater efficiency than fertilizers in calcareous soil.

Graphical abstract: Open raceway pond and constructed wetland coupled with wastewater treatment and bio-ethanol production

Smectites are effective binders of aflatoxin in aqueous solutions. Unfortunately, their efficacy is reduced in guts because of interference by biomolecules and essential nutrients within the gut. Tunnel structures in palygorskite and sepiolite may function as molecular sieves and may, therefore, serve as alternatives or complements to smectites in binding aflatoxins but not larger biological compounds. The objective of the current work was to determine the effect of heat treatment on aflatoxin B1(AfB1) adsorption and selectivity for biomolecules by two palygorskites (Plg_PK and Plg_CN), sepiolite (Sep), and a palygorskite-smectite mixture (Plg-Sm) in comparison with a smectite (Sm-37GR). The clays were heated at 250, 400, 500, and 600°C while phase and structural changes were characterized by X-ray diffraction and infrared spectroscopy. Comparative AfB1adsorption was determined in aqueous and in simulated gastric fluids. The clay structures collapsed irreversibly in Sm-37GR and folded in fibrous clays with heating at 400°C or more. Sm-37GR adsorbed more AfB1than all of the other clays; the estimated adsorption capacity followed the trend Sm-37GR (44 g kg–1) > Plg_PK (18.12 g kg–1) > Sep (12.7 g kg–1) > Plg_CN (11.4 g kg–1) > Plg-Sm (9.0 g kg–1). This trend appeared to be correlated with the abundance of smectite in the clays. Sepiolite had greater binding strength for AfB1 than the other clays. With intact clay structures, heating induced a negligible effect on AfB1adsorption by the fibrous clays while in Sm-37GR and Plg-Sm, adsorption increased with heating at 250°C. Tunnel folding and structural collapse that had occurred at 400°C caused an abrupt decline in AfB1adsorption irrespective of the clay type. The sepiolite clay adsorbed the least pepsin (370 g kg–1) while smectite adsorbed the most (1430 g kg–1). Consequently, in the simulated gastric fluid, adsorption declined by 25–30% in sepiolite, 52–60% in smectite, and remained unaffected in the palygorskites. Aflatoxin B1adsorption probably occurred through H-bonding at the surface with the silanol group in palygorskite and sepiolite. No evidence that AfB1molecules occupied the tunnels of the natural or heated palygorskite or sepiolite was observed in the present study. Palygorskite and sepiolite had a much smaller adsorption capacity for AfB1than the smectite but also adsorbed less pepsin; therefore, both may be effective aflatoxin binders in gastrointestinal systems.

Crop response to manganese (Mn) application is often erratic in the alkaline and calcareous soils due to its strong immobilization by chemical and microbial oxidation processes. Microbial redox reactions considerably affect soil Mn bioavailability and plant growth through sorption and desorption processes. Exploring the mechanisms of Mn-oxidizing (MnOB) and Mn-reducing bacteria (MnRB) in conjunction with mineral fertilizers could be an eloquent approach for enhancing nutrient availability to plant in calcareous soil. The objectives of the present study are to understand the mechanisms of Mn bioavailability via microbial redox cycling and to evaluate the effectiveness of Leptothrix discophora(MnOB) and Bacillus polymyxa(MnRB) inoculation together with mineral fertilizers (NPK) on wheat yield and soil nutrient bioavailability in a calcareous soil. A pot experiment was carried out under greenhouse conditions. The experiment comprised of six treatments (viz., control, half dose of NPK fertilizer (½NPK, 75–50-50 mg kg−1), NPK fertilizer (150–100-100 mg kg−1), ½NPK + MnOB, ½NPK + MnRB, and ½NPK + MnOB + MnRB) laid down in a completely randomized design with three replicates. The root weight, shoot weight, and grain yield were recorded. Moreover, soil pH, electrical conductivity (EC), and organic matter (SOM) as well as post-harvest availability of macro- and micronutrients were determined. The combination of MnOB and MnRB (redox processes) in the presence of ½NPK reduced soil pH value by 12% compared to control, whereas enhanced plant micronutrient contents by 19 to 28% compared to NPK treatment. Sole application of ½NPK and in concoction with MnOB and MnRB significantly increased wheat grain yield by 41 and 90%, whereas SOM contents by 2 and 14%, respectively. Similarly, a significant increase in post-harvest soil macro- and micronutrients further confers positive effects of MnOB and MnRB. Integrated use of soil microbial resources (MnOB, MnRB) and mineral fertilizers is very effective way to enhance the bioavailability of macro- and micronutrients in a calcareous soil.

The accumulation of rare earth oxides (REOs) in soils is linked with application of nanoscale phosphatic fertilizers, but their effects on earthworm species are poorly understood. We investigated the impacts of nanoscale and bulk-REOs of lanthanum and ytterbium (La2O3, Yb2O3) at low (25, 50 mg kg−1), intermediate (100, 200 mg kg−1) and high (500, 1000 mg kg−1) concentrations on soil quality and earthworm health. The bioaccumulation of nanoscale and bulk Yb2O3was 12–28% greater than La2O3and occurred in a dose-dependent manner. At 100 mg kg−1, nanoscale and bulk La2O3and Yb2O3induced earthworm mortality by 33–35% and 13–15%, and reduced reproduction by 10–32% and 10–12%, respectively. Ultrastructural observations reveal that nanoscale and bulk REO at 500–1000 mg kg−1induced abnormalities in internal organelles, including mitochondria, Golgi apparatus and chloragosomes. Nanoscale REOs significantly reduced earthworm digestive and cast enzymes by 20–80% at medium and high concentrations as compared to bulk materials. Earthworms reduced REO toxicity in the soil by minimizing exposure to microbial biomass carbon and soil enzymes. The data show that REOs beyond 50–100 mg kg−1adversely impact soil microbiota; these findings provide important understanding of the fate and effects of REOs in agricultural systems.

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 thiooxidansIW16. 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−1of 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 (H2SO4formation), 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.

Greenhouse studies were undertaken to evaluate the genetic performance of two cucumber genotypes (Long Green and Summer Green) at four salinity levels (0, 25, 50, and 100 mM NaCl). Seeds were pretreated with 50 mg salicylic acid (SA) L−1and 25 mg kinetin (Kin) L−1. Under hydroponic conditions, seed pretreatment with Kin significantly increased shoot and root dry biomass and reduced the salt injury index in both genotypes. SA reduced the salt injury index of Long Green cucumbers. In a pot experiment, Kin treatment reduced Na+and increased K+concentration, photosynthesis, and chlorophyll content in both genotypes, compared to SA under saline soil conditions. Kin treatment improved fruit yield in both genotypes, while SA had a statistically significant effect on Long Green fruit yield. The application of SA and Kin enhanced salinity tolerance in both genotypes by the activation of antioxidants, especially superoxide dismutase, peroxidase, and catalase, which offset oxidative injury. Summer Green exhibited better salt tolerance and improved osmoregulation that resulted in higher fruit yield than Long Green. It was concluded that cucumber genotypes differed in salt tolerance, and seed pre-treatment with Kin minimized salt stress injury, even in sensitive genotype which could sustain crop production under saline conditions.

AbstractCrop production in a rainfed area is constrained by inappropriate management of soil and water by the resource-poor farmers. The present study addresses this issue through integration of practices for soil water conservation (SWC) and soil fertility enhancement as well. Extensive experimentation on wheat-maize was undertaken for two years (2004−2006) on the fields of eight farmers representing two soil types; Rajar (Typic Ustorthent; USDA soil taxonomy) and Guliana (Udic Haplustalf; USDA soil taxonomy) in the Gujar Khan Tehsil of Rawalpindi District, Pakistan. Four treatments consisting of: no SWC +farmer’s rate of fertilizer application (FP), no SWC+improved fertilizer application (IF), SWC practices i.e., deep plowing, bund improvement, plowing across contour+FP (SWC+FP) and SWC+IF. Wheat and maize grain yields in SWC and IF were statistically higher than in the treatments with no SWC and FP, respectively. Compared with the control without any treatment, increase in water use efficiency of both maize and wheat crop was higher in SWC+IF followed by IF alone. On the average, Guliana soil series showed better response to all treatments than Rajar soil. The integrated application of SWC and IF practices increased crop yields in the rainfed area.

Purpose of the current study was to investigate the effects of constantly wet and dried-rewetted sediments on root functional traits of emerged macrophytes and their nutrients removal abilities. It is based on the hypothesis that root characteristics and nutrients removal abilities of plants will be altered in the course of sediment desiccation. Four emerged macrophytes including two fibrous-root plants (Canna indicaand Acorus calamus) and two thick-root plants (Alocasia cucullataand Aglaonema commutatum) were investigated for their root functional traits and rhizoperformance in both wet and dried-rewetted sediments. Results showed that sediment desiccation followed by rewetting substantially altered the root functional traits (root surface area, radial oxygen loss, and root activity) of plants due to adverse changes in morphological characteristics (porosity, bulk density, particle density) of dried-rewetted sediments than by wet sediments. Consequently, limited plants growth and removal of nitrogen (N), phosphorus (P) and dissolved organic carbon (DOC) were recorded in dried-rewetted sediments and their pore water than in wet sediments. Radial oxygen loss from plant roots correlated positively with root functional traits, plants growth, and removal of N, P and DOC from pore water and sediment in both sediment types. Among the macrophyte species, the fibrous-root plants having advantages root functional traits, greatly influenced the rhizospheric conditions (pH, dissolved oxygen and redox potential), and demonstrated higher N, P and DOC reduction from both sediment types. While, the thick-rooted plants with thick diameter roots (D> 1 mm) and higher rhizome exhibited longer life-span in both sediment types.

Peganum harmala L. (Zygophyllaceae) is an herb native to arid and semiarid regions of Central Asian deserts. This study investigated the effects of ethanol extracts of P. harmala seeds on the olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), i.e., adult repellency, reproductive activity, and larval growth, as well as parasitism levels by Psyttalia concolor (Szépligeti). Olive fruit treated with 2% extract reduced B. oleae oviposition. In choice tests, female B. oleae spent >99% of their time foraging on untreated fruit rather than P. harmala-treated fruit. These changes in ovipositional behavior resulted in a nearly 30-fold decrease in oviposition marks on treated fruit compared with untreated fruit during a 48 h exposure period. When female B. oleae were fed liquid diet containing 0.2% P. harmala extract, there was no effect on the number of ovipositional marks on exposed fruit, but up to 21.4% of the deposited eggs were deformed. SDS-polyacrylamide gel electrophoresis analyses of deformed eggs revealed that some protein bands were missing. Consequently, the number of offspring produced by treated females was lower than by untreated females. Neither the sex ratio nor body size of the fly’s offspring were affected by adults fed diet containing 0.2% P. harmala extract. However, there was a slightly prolonged developmental time from egg to adult. Parasitism of larval B. oleae by P. concolor was not affected by infested fruit treatment with 2% P. harmala extract. P. harmala extracts as a potential control for insect pest species are discussed.

Three plant materials that are common in Pakistan, rhizomes of Curcuma longa (L.) (turmeric), leaves of Azadirachta indica A. Juss. (neem), and leaves of Trigonella foenum-graecum L. (fenugreek), were evaluated for their repellency against the adults of the three species of stored-product insects, Tribolium castaneum (Herbst), Sitophilus granarius (L.), and Rhyzopertha dominica(F.). Turmeric powder was the most effective of the three against S. granarius and R. dominica. and also the most effective of the solvent extracts against T. castaneum. For each plant material, the petroleum ether extracts were more effective than the acetone and ethanol extracts. The petroleum ether extract of fenugreek deteriorated much faster than the similar extracts of turmeric and neem. The petroleum ether extract of neem was the most effective of the three plant materials against penetration by R. dominica.