Phosphate additives promote humic acid carbon and nitrogen skeleton formation by regulating precursors and composting bacterial communities.

This study aimed to compare the effect of different phosphate additives including superphosphate (CP) and MP [Mg(OH)2 + H3PO4] on nitrogen conversion, humus fractions formation and bacterial community in food waste compost. The results showed the ratio of humic acid nitrogen in total nitrogen (HA-N/TN) in CP increased by 49 %. Ammonium nitrogen accumulation was increased by 75 % (CP) and 44 % (MP). Spectroscopic techniques proved that phosphate addition facilitated the formation of complex structures in HA. CP enhanced the dominance of Saccharomonospora, while Thermobifida and Bacillus were improved in MP. Structural equation modeling and network analysis demonstrated that ammonium nitrogen can be converted to HA-N and has positive effects on bacterial composition, reducing sugars and amino acids, especially in CP with more clustered network and synergic bacterial interactions. Therefore, the addition of phosphate provides a new idea to regulate the retained nitrogen toward humification in composting.

Nitrogen-fertilizer addition to an agricultural soil enhances biogenic non-extractable residue formation from 2-13C,15N-glyphosate.

Glyphosate and nitrogen (N) or (P) phosphorus fertilizers are often applied in combination to agricultural fields. The additional P or N supply to microorganisms might drive glyphosate degradation towards sarcosine/glycine or aminomethylphosphonic acid (AMPA), and consequently determine the speciation of non-extractable residues (NERs): harmless biogenic NERs (bioNERs) or potentially hazardous xenobiotic NERs (xenoNERs). We therefore investigated the effect of P or N-fertilizers on microbial degradation of glyphosate and bioNER formation in an agricultural soil. Four different treatments were incubated at 20 °C for 75 days as follows; I: no fertilizer (2-13C,15N-glyphosate only, control), II: P-fertilizer (superphosphate + 2-13C,15N-glyphosate, effect of P-supply), III: N-fertilizer (ammonium nitrate + 2-13C,15N-glyphosate, effect of N-supply) and IV: 15N-fertilizer (15N-ammonium nitrate + 2-13C-glyphosate, differentiation between microbial assimilations of 15N: 15N-fertilizer versus 15N-glyphosate). We quantified 13C or 15N in mineralization, extractable residues, NERs and in amino acids (AAs). At the end, mineralization (36-41 % of the 13C), extractable 2-13C,15N-glyphosate/2-13C-glyphosate (0.42-0.49 %) & 15N-AMPA (1.2 %), and 13C/15N-NERs (40-43 % of the 13C, 40-50 % of the 15N) were comparable among treatments. Contrastingly, the 15N-NERs from 15N-fertlizer amounted to only 6.6 % of the 15N. Notably, N-fertilizer promoted an incorporation of 13C/15N from 2-13C,15N-glyphosate into AAs and thus the formation of 13C/15N-bioNERs. The 13C/15N-AAs were as follows: 16-21 % (N-fertilizer) > 11-13 % (control) > 7.2-7.3 % (P-fertilizer) of the initially added isotope. 2-13C,15N-glyphosate was degraded via the sarcosine/glycine and AMPA simultaneously in all treatments, regardless of the treatment type. The percentage share of bioNERs within the NERs in the N-fertilized soil was highest (13C: 80-82 %, 15N: 100 %) compared to 53 % (13C & 15N, control) and to only 30 % (13C & 15N, P-fertilizer). We thus concluded simultaneous N & glyphosate addition to soils could be beneficial for the environment due to the enhanced bioNER formation, while P & glyphosate application disadvantageous since it promoted xenoNER formation.

Enhancing the transformation of carbon and nitrogen organics to humus in composting: Biotic and abiotic synergy mediated by mineral material.

To investigate the conversion of carbon and nitrogen organic matter to humus mediated by mineral material additives through biotic and abiotic pathways, three chicken manure composting experiments were conducted using calcium superphosphate (CS) and fly ash (FA). Results showed that CS and FA promoted carbon and nitrogen organic degradation and improved compost maturity. The ratio of humic acid-like to fulvic acid-like substances for FA (30) was significantly higher than for control (18) and CS (13). Excitation-emission-matrix spectra and parallel factor analysis identified a higher transformation of protein-like components into humic-like components in FA. Network analysis showed that CS improved compost maturity by promoting the rapid conversion of humus precursors to humus, while FA increased the richness and diversity of the microbial community, such as Chloroflexi, the unique phylum in FA. Overall, CS and FA facilitated the humification process through abiotic and biotic pathways, and FA had better humification performance.

Dynamics of Phosphorus and Biostimulants on Agro-Morphology, Yield, and Essential Oil Profile of German Chamomile (Matricaria chamomilla L.) Under Acidic Soil Conditions of the Western Himalaya.

German chamomile (Matricaria chamomilla L.) is a promising and easy to cultivate crop under suitable nutrient supply conditions, but acidic soils of Indian western Himalayas limit the availability of phosphorus to the plant and reduce flower production. Thus, a field experiment was conducted for two consecutive seasons (2018-2019 and 2019-2020) to study the effect of phosphorus dynamics and biostimulant application on the agro-morphological traits, essential oil (EO) yield, and chemical constituents of German chamomile in the mid hills of the western Himalayan region. The experiment consisted of 12 treatments, four phosphorus fertilizer levels (0, 30, 60 and 90 kg ha-1) and three biostimulants levels (control, amino acid at 5 mL L-1, and humic acid at 10 mL L-1). The experiment was replicated three times in a factorial complete randomized block design (FRBD). Agro-morphological and yield characteristics were significantly higher in phosphorus at 90 kg ha-1 and humic acid application compared to the control. Dry flower and EO yield was 17.87 and 26.76% higher with the 90 kg ha-1 phosphorus application while 2.45 and 5.79% higher in humic acid at 10 mL L-1 compared to the control. The EO constituents viz., chamazulene was 12.04 and 8.85% higher in phosphorus at 90 kg ha-1 and humic acid at 10 mL L-1 application compared to the control. On the other hand, α-bisabolol oxide B and α-bisabolol oxide A were decreased with increase in phosphorus application. This study presents novel facts, elucidation, and explanation for farmers and industrialists to produce German chamomile in acidic soils by integrating biostimulants with phosphorus fertilization and getting maximum yield and quality EO.

Effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions during pig manure composting.

This study investigated the effects of dicyandiamide, phosphogypsum and superphosphate on greenhouse gas emissions and compost maturity during pig manure composting. The results indicated that the addition of dicyandiamide and phosphorus additives had no negative effect on organic matter degradation, and could improve the compost maturity. Adding dicyandiamide alone reduced the emissions of ammonia (NH3), methane (CH4) and nitrous oxide (N2O) by 9.37 %, 9.60 % and 31.79 %, respectively, which was attributed that dicyandiamide effectively inhibited nitrification to reduce the formation of N2O. Dicyandiamide combined with phosphogypsum or superphosphate could enhance mitigation of the total greenhouse gas (29.55 %-37.46 %) and NH3 emission (18.28 %-21.48 %), which was mainly due to lower pH value and phosphoric acid composition. The combination of dicyandiamide and phosphogypsum exhibited the most pronounced emission reduction effect, simultaneously decreasing the NH3, CH4 and N2O emissions by 18.28 %, 38.58 % and 36.14 %, respectively. The temperature and C/N content of the compost were significantly positively correlated with greenhouse gas emissions.

Effect of Arbuscular Mycorrhizal Fungi Isolated From Rock Phosphate Mine and Agricultural Soil on the Improvement of Wheat Plant Growth.

The improvement of plant growth and yield becomes crucial to feed the rising world population, especially in harsh conditions, drought, salt stress, lack of nutrition, and many other challenges. To cope with these stresses, plants developed an adaptation strategy (mycorrhiza), which is an efficient way to reinforce their growth and resistance. For this purpose, we studied the influence of mycorrhizal fungi isolated from a natural rock phosphate mine in the vicinity of some native plants and agricultural soil to assess their capacity in increasing the growth, nutritional profile improvement, and biochemical parameters in the inoculated wheat plants. Results showed a high diversity of isolated arbuscular mycorrhizal fungi (AMF) spores in the agricultural soil, and less diversity in the natural phosphate samples, where three main genera were identified: glomus, gigaspora, and acaulospora. The chlorophyll content increased by 116% in the native inoculum (NM) flowed by Glomus sp2 from agricultural soil (98%) compared to non-mycorrhized plants, which significantly impact the growth and plant biomass (an increase of 90 and 73%, respectively). The same rate of change was shown on total phenolic compounds with an increase of 64% in the plants inoculated with Glomus sp2 in the presence of TSP, compared to the non-mycorrhized plants. In conclusion, the inoculation of wheat plants with AMF spores improved plants' growth via the increase in the density of the root system, which implies better assimilation of nutrients, especially in mycorrhizal plants with phosphorus fertilization regime, triple superphosphate (TSP) or natural rock phosphate (RP). This improvement of the physiological and biochemical parameters (chlorophyll contents and phenolic compound) of the treated plants reflected the positive impact of AMF, especially those originating from RP. AMF in phosphate mine could be an important source of inoculum to improve plant nutrient efficiency with the direct use of RP as fertilizer.

Effect of superphosphate addition on heavy metals speciation and microbial communities during composting.

Superphosphate fertilizer (SSP) as an additive can reduce the nitrogen loss and increase available phosphorus in composting but few studies investigated the effect of SSP addition on heavy metal and microbial communities. In this study, different ratios (10%, 18%, 26%) of SSP were added into pig manure composting to assess the changes of heavy metal (Cu, Mn, As, Zn, and Fe) fractions, bacterial and fungal communities as well as their interactions. SSP addition at 18% had lower ecological risk but still increased the bioavailability of Cu, Mn, and Fe in composts compared to control. Adding 18% SSP into compost decreased bacterial number and increased the fungal diversity compared to CK. Redundancy analysis indicated heavy metal fractions correlated significantly with bacterial and fungal community compositions in composting with 18% SSP. Network analysis showed adding 18% SSP increased microbial interaction and positive cooperation especially enhanced the proportion of Proteobacteria and Ascomycota.

Ingestion of remediated lead-contaminated soils affects the fecal microbiome of mice.

The relationship between ingestion of diets amended with a Pb-contaminated soil and the composition of the fecal microbiome was examined in a mouse model. Mice consumed diets amended with a Pb-contaminated soil in its native (untreated) state or after treatment for remediation with phosphoric acid or triple superphosphate alone or in combination with iron-waste material or biosolids compost. Subacute dietary exposure of mice receiving treated soil resulted in modulation of the fecal intestinal flora, which coincided with reduced relative Pb bioavailability in the bone, blood and kidney and differences in Pb speciation compared to untreated soil. Shifts in the relative abundance of several phyla including Verrucomicrobia, Tenericutes, Firmicutes, Proteobacteria, and TM7 (Candidatus Saccharibacteria) were observed. Because the phyla persist in the presence of Pb, it is probable that they are resistant to Pb. This may enable members of the phyla to bind and limit Pb uptake in the intestine. Families Ruminococcaceae, Lachnospiraceae, Erysipelotrichaceae, Verrucomicrobiaceae, Prevotellaceae, Lactobacilaceae, and Bacteroidaceae, which have been linked to health or disease, also were modulated. This study is the first to explore the relationship between the murine fecal microbiome and ingested Pb contaminated soils treated with different remediation options designed to reduce bioavailability. Identifying commonalities in the microbiome that are correlated with more positive health outcomes may serve as biomarkers to assist in the selection of remediation approaches that are more effective and pose less risk.

Superphosphate, biochar, and a microbial inoculum regulate phytotoxicity and humification during chicken manure composting.

The germination index (GI) is the best index for evaluating compost phytotoxicity and maturity. In order to improve GI and reduce phytotoxicity of chicken manure compost, superphosphate, biochar, and a microbial inoculum were added in this study. Maturity indices (pH, electrical conductivity, and GI), water-soluble ion, organic matter, humic acid, humic precursor contents, and the bacteria community were analyzed during the experiment. NH4+, volatile fatty acids, and humic acid strongly affected the GI, which increased as the humic acid content increased and the volatile fatty acid and NH4+ contents decreased. The three additives affected compost maturity differently. Adding biochar decreased microbial diversity and complexity, but improved the GI mainly by affecting abiotic factors. Adding the microbial inoculum increased biotic activity and promoted humus and precursor formation. Superphosphate activated core functional bacteria and increased bacterial diversity and complexity, and 16 genera and 2 phyla (Gemmatimonadota and Chloroflexi) were found only in this composting pile. Superphosphate markedly accelerated humification and decreased the salt (NH4+ and NO3-) and heavy metal ion (Cu2+, Cd2+, Cr3+) contents, forming stable substances to reduce the key phytotoxic matters, which in turn decreased the compost phytotoxicity and improved the GI. These results provide a new sight for promoting maturity by functional material regulation in composting.

Investigating triple superphosphate for lead removal from aqueous solutions.

The aim of this research is to investigate monocalcium phosphate monohydrate [Ca(H2PO4)2. H2O] also called triple superphosphate (TSP) for the removal of lead (Pb) from aqueous solutions. In this study, TSP was selected amongst various phosphate-based materials and fertilizers to act as the source of orthophosphate (PO43-) which is a powerful tool for metal fixation in soil and water. Thermodynamic equilibrium dissolution-precipitation relationships for the systems of Pb-H2O and Pb-PO43--H2O were drawn with the aid of Eh-pH stability diagrams to determine the predominance areas of different species. The lead phosphate compounds, identified through the stability area diagrams, were verified with the batch precipitation tests performed with standard solutions of lead and TSP at different conditions. It was observed that, depending upon solution conditions, TSP can precipitate 99.9% of the lead from the solution. Lead precipitates, analyzed by x-ray diffraction, showed the formation of lead phosphate compounds. The mechanism of TSP for the removal of lead from aqueous solutions is discussed.

Do soil cadmium concentrations decline after phosphate fertiliser application is stopped: A comparison of long-term pasture trials in New Zealand?

Decreasing soil cadmium (Cd) is one method of removing Cd from the food chain. Phosphorus (P) fertilisers are a major source of Cd inputs into soil. Stopping P fertiliser should theoretically decrease Cd inputs and soil Cd accumulation, but there are few field data to show if this occurs. We examined three long-term grazed pasture trials in New Zealand (Ballantrae, Winchmore and Whatawhata) where P fertiliser had been applied (from 10 to 100 kg P ha-1 yr-1) for up to six years and then stopped for 10 to 26 years. Stopping P fertiliser applications reduced soil Cd concentrations at Winchmore and Whatawhata where P had been applied at ≥34 kg P ha-1 yr-1. No reductions occurred below this rate nor at Ballantrae where only 10 years post P-application data were available. Decreases were ascribed to moderate rainfall (1630 mm at Whatawhata and 740 mm rainfall plus 770 mm irrigation at Winchmore) that enhanced Cd leaching and may have been aided at Winchmore by a decrease in soil pH over time (0.4 units). However, because stopping P fertiliser inputs may quickly impair pasture production, additional strategies may be required to decrease soil Cd quickly.

Decreased Methane Emissions Associated with Methanogenic and Methanotrophic Communities in a Pig Manure Windrow Composting System under Calcium Superphosphate Amendment.

With the rapid growth of livestock breeding, manure composting has evolved to be an important source of atmospheric methane (CH4) which accelerates global warming. Calcium superphosphate (CaSSP), as a commonly used fertilizer, was proposed to be effective in reducing CH4 emissions from manure composting, but the intrinsic biological mechanism remains unknown. Methanogens and methanotrophs both play a key role in mediating CH4 fluxes, therefore we hypothesized that the CaSSP-mediated reduction in CH4 emissions was attributed to the shift of methanogens and methanotrophs, which was regulated by physicochemical parameter changes. To test this hypothesis, a 60-day pig manure windrow composting experiment was conducted to investigate the response of CH4 emissions to CaSSP amendment, with a close linkage to methanogenic and methanotrophic communities. Results showed that CaSSP amendment significantly reduced CH4 emissions by 49.5% compared with the control over the whole composting period. The decreased mcrA gene (encodes the α-subunit of methyl-coenzyme M reductase) abundance in response to CaSSP amendment suggested that the CH4 emissions were reduced primarily due to the suppressed microbial CH4 production. Illumina MiSeq sequencing analysis showed that the overall distribution pattern of methanogenic and methanotrophic communities were significantly affected by CaSSP amendment. Particularly, the relative abundance of Methanosarcina that is known to be a dominant group for CH4 production, significantly decreased by up to 25.3% accompanied with CaSSP addition. Only Type I methanotrophs was detected in our study and Methylocaldum was the dominant methanotrophs in this composting system; in detail, CaSSP amendment increased the relative abundance of OTUs belong to Methylocaldum and Methylobacter. Moreover, the increased SO42- concentration and decreased pH acted as two key factors influencing the methanogenic and methanotrophic composition, with the former has a negative effect on methanogenesis growth and can later promote CH4 oxidation at a low level. This study deepens our understanding of the interaction between abiotic factors, function microbiota and greenhouse gas (GHG) emissions, as well as provides implication for practically reducing composting GHG emissions.

Coupling effects of phosphorus fertilization source and rate on growth and ion accumulation of common bean under salinity stress.

Many agricultural regions in arid and semiarid climate zone need to deal with increased soil salinity. Legumes are classified as salt-sensitive crops. A field experiment was performed to examine the application of phosphorus (P) fertilizer source and rate on growth, chlorophylls and carotenoid content, DNA and RNA content and ion accumulation in common bean (Phaseolus vulgaris L.) cultivated under salinity stress. An experimental design was split-plot with three replicates. The main plots included two P sources, namely single superphosphate (SP) and urea phosphate (UP). The sub-plots covered four P rates, i.e., 0.0, 17.5, 35.0, and 52.5 kg P ha-1. All applied P fertilization rates, in both forms, increased plant height, leaf area, dry weight of shoots and roots per plant, and total dry weight (TDW) in t ha-1. The highest accumulation of N, P, K+, Mg2+, Mn2+, Zn2+, and Cu2+ was determined in the shoot and root of common bean, while 35 kg of P per ha-1 was used compared to the other levels of P fertilizer. The highest P rate (52.5 kg ha-1) resulted in a significant reduction in Na+ in shoot and root of common bean. The response curve of TDW (t ha-1) to different rates of P (kg ha-1) proved that the quadratic model fit better than the linear model for both P sources. Under SP, the expected TDW was 1.675 t ha-1 if P was applied at 51.5 kg ha-1, while under UP, the maximum expected TDW was 1.875 t ha-1 if P was supplied at 42.5 kg ha-1. In conclusion, the 35.0 kg P ha-1 could be considered the best effective P level imposed. The application of P fertilizer as urea phosphate is generally more effective than single superphosphate in enhancing plant growth and alleviating common bean plants against salinity stress.

A comparison of microwave and ultrasound routes to prepare nano-hydroxyapatite fertilizer improving morphological and physiological properties of maize (Zea mays L.).

Hydroxyapatite nanoparticles have a remarkable potential to be used as nano-fertilizers with great effects on improving the yield of plants. These nano-compounds were synthesized using microwave and ultrasound methods, which decrease the particle size distribution of the products. To investigate the effects of two types of simple and triple superphosphate fertilizers on some properties of maize plant (Zea mays L.), a factorial experiment was conducted based on a completely randomized block design. The fertilizer treatments included in this study were simple superphosphate, triple superphosphate, microwave nano-hydroxyapatite, and ultrasound nano-hydroxyapatite and examined at five concentration levels. The results showed that the application of nano-hydroxyapatite phosphate fertilizers improved the growth and physiological properties of maize plant. This would raise better results in comparison to the simple and triple superphosphate fertilizers. Considering the positive effects of nano-hydroxyapatite fertilizers and high production levels, the results of this experiment revealed that the synthetic nano-hydroxyapatite methods prevent phosphorus loss; therefore, it is recommended to use nano-phosphate fertilizers in food resource management to achieve a favorable quantitative yield. Moreover, they can be regarded as a favorable solution to deal with the environmental problems.

Valorization of calcium phosphite waste as phosphorus fertilizer: Effects on green manure productivity and soil properties.

The potential to use calcium phosphite (Ca-Phi) as phosphorus (P) fertilizer may represent an effective recycling of P-containing by-products. A greenhouse experiment was conducted to investigate the effect of Ca-Phi (38 kg P ha-1) on soil properties and the growth parameters of four green manure species in clay and sandy soils using Ca-Phi, TSP (triple superphosphate) and control (no fertilization) as treatments. Eight weeks after sowing, we measured aboveground biomass yield, phosphite (Phi) concentration in plant biomass, different soil P pools as well as microbial biomass nutrients. Compared to control, the addition of Ca-Phi did not negatively affect green manure yield, except for lupine (Lupinus albus L.) in clay soil. The Phi concentration in plant biomass varied across species and soil type with a maximum concentration of about 400 mg Phi kg-1 for mustard (Brassica juncea L.) in clay soil. Compared to control, TSP and Ca-Phi fertilization had a similar effect on different P pools and microbial biomass nutrients (C, N and P) although the response was soil-type dependent. In the sandy soil, after Ca-Phi addition the amount of available P (PNHCO3) increased to the same extent as in the TSP treatment (i.e. around 6 mg P kg-1) suggesting that Ca-Phi was, at least partly, oxidized. In the clay soil with high P fixing capacity, Ca-Phi promoted higher PNaHCO3 than TSP likely due to different solubility of chemical P forms. Additional studies are however required to better understand soil microbial responses and to quantify the P agronomical efficiency for the following crop under Ca-Phi fertilization.

Role of phosphorous additives on nitrogen conservation and maturity during pig manure composting.

This study compared different types and addition amounts of phosphorous additives on nitrogen conservation and maturity during pig manure composting. Phosphogypsum and superphosphate were applied with the same amount of phosphorus (5% of the initial total nitrogen, molar basis) or weight (10% of initial dry matter) and compared to a control treatment without additives. Results show that phosphorous additives could effectively conserve nitrogen. Adding phosphogypsum could significantly reduce NH3 emission and total nitrogen loss, but increase N2O emission. Application of 10% superphosphate mitigated NH3 emissions and total nitrogen loss but inhibited the organic matter degradation and compost maturity. More importantly, with the addition of 5% initial total nitrogen (i.e., 2.5% dry matter), superphosphate could synchronously reduce NH3 and N2O emissions and improve compost quality by introducing additional nutrients into the compost. In comprehensive evolution of gaseous emissions, nitrogen loss, and compost maturity, superphosphate addition with 2.5% of initial dry matter was suggested to be used in practice.

Microbial succession and molecular ecological networks response to the addition of superphosphate and phosphogypsum during swine manure composting.

This study assessed the effects of superphosphate (SPP) and phosphogypsum (PPG) on the bacterial and fungal community succession and molecular ecological networks during composting. Adding SPP and PPG had positive effects on the bacterial richness and diversity, negative effects on the fungal richness and diversity. The microbial diversity and richness were higher in PPG than SPP. Non-metric multidimensional scaling analysis clearly separated SPP and PPG from the control treatment with no additives. The dominant genera comprised Turicibacter, Bacillus, norank_o_SBR1031, Thermobifida, norank_f_Limnochordaceae, Truepera, Thermopolyspora, Mycothermus, Dipodascus, Thermomyces, and unclassified_p_Ascomycota. In all treatments, the major bacterial species differed clearly in the later thermophilic, cooling, and maturation composting stages, whereas the main fungal species varied significantly in the thermophilic stage. The changes in the dominant microorganisms in SPP and PPG may have inhibited or promoted the degradation of organic matter during various composting stages. Adding SPP and PPG led to more complex bacterial networks and less complex fungal networks, where SPP had more adverse effects on the fungal networks than PPG. SPP and PPG could potentially alter the co-occurrence patterns of the bacterial and fungal communities by changing the most influential species. SPP and PPG changed the composition and succession of the microbial community by influencing different physiochemical properties during various composting stages where the pH was the main explanatory factor. Overall, this study provides new insights into the effects of SPP and PPG on the microbial community and its interactions during composting.

Application of biochar and inorganic phosphorus fertilizer influenced rhizosphere soil characteristics, nodule formation and phytoconstituents of cowpea grown on tropical soil.

The effect of biochar alone or co-applied with triple superphosphate on rhizosphere soil characteristics, nodule formation, phytoconstituents and antioxidant property of cowpea (Vigna uguiculata) is yet to be adequately examined in sub Saharan Africa. A field experiment was conducted where cowpea (Vigna unguiculata) was grown in a tropical sandy loam soil amended with biochar at 1.5 t ha-1 and 2.5 t ha-1 solely or together with inorganic phosphate fertilizer (Triple superphosphate), applied at a rate of 60 kg P ha -1. At 50% flowering, changes in selected rhizosphere soil properties (pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity), nodule count, phytochemicals (phenols, flavonoids, alkaloids, tannins, saponins) and antioxidant property of cowpea roots and leaves were determined by standard laboratory procedures. Differences between means of the measured parameters were established using ANOVA, and relationships among the parameters were explored using Pearson correlation (p < 0.05). Addition of biochar solely or in combination with TSP significantly (p < 0.05) increased soil pH, total nitrogen, available phosphorus, soil organic carbon, cation exchange capacity and root nodule count. Flavonoids, phenols, alkaloids, saponin, tannin contents and antioxidant activity in the roots and leaves were significantly (p < 0.05) higher in the amended soils compared with the unamended soil. Similarly, soil flavonoids, phenols, alkaloids and antioxidant activity were significantly higher in amended soils compared with control. Significant, positive inter and intra correlation with varying strength was found between soil properties, nodule number and phytoconstituents. This is an indication that biochar can be co-applied with triple superphosphate to sustain soil fertility, improve nodulation and enhance concentrations of phytoconstituents in soil, cowpea roots and leaves.

A low cost of phosphate-based binder for Mn2+ and NH4+-N simultaneous stabilization in electrolytic manganese residue.

Electrolytic manganese residue (EMR) is a solid waste remained in filters after using sulfuric acid to leaching manganese carbonate ore. EMR contains high concentration of soluble manganese (Mn2+) and ammonia nitrogen (NH4+-N), which seriously pollutes the environment. In this study, a low cost of phosphate based binder for Mn2+ and NH4+-N stabilization in EMR by low grade-MgO (LG-MgO) and superphosphate was studied. The effects of different types of stabilizing agent on the concentrations of NH4+-N and Mn2+, the pH of the EMR leaching solution, stabilizing mechanisms of NH4+-N and Mn2+, leaching test and economic analysis were investigated. The results shown that the pH of the EMR leaching solution was 8.07, and the concentration of Mn2+ was 1.58 mg/L, both of which met the integrated wastewater discharge standard (GB8978-1996), as well as the concentration of NH4+-N decreased from 523.46 mg/L to 32 mg/L, when 4.5 wt.% LG-MgO and 8 wt.% superphosphate dosage were simultaneously used for the stabilization of EMR for 50 d Mn2+ and NH4+-N were mainly stabilized by Mn3(PO4)2·2H2O, MnOOH, Mn3O4, Mn(H2PO4)2·2H2O and NH4MgPO4·6H2O. Economic evaluation revealed that the treatment cost of EMR was $ 11.89/t. This study provides a low-cost materials for NH4+-N and Mn2+ stabilization in EMR.