| Biochar is a carbon-rich substance produced by pyrolysis of organic matter (usually plant material) in an oxygen limited environment. At present, several pyrolysing technologies are used to generate the biochars from different feedstocks. The pyrolysis entails the heating of organic feedstocks under limited oxygen supply, to produce the biochars coupled with various types of bio-products such as bio oil, and gas etc. Biochars produced at higher temperatures are very resistant to microbial degradation in soils, but can change the soil physico-chemical properties. The biochar addition to soil is a strategy to reduce the carbon fluxes from soil to the environment and additionally, it improves soil fertility. In this study, a series of experiments have been conducted to investigate the influence of biochars generated from various feedstocks, on soil microbial community and fertility in acidic soils.In first experiment of this study, several biochars were produced from different feedstocks Saccharum spontaneum, Thalia delbata, Cyperus alternifolius, Erianthus ravennae, almond leaves, fruit peels and swine manure) by pyrolyzing at 300℃ and 500℃ for 2 or 4h respectively. The physicochemical properties of the biochars were investigated to check the influence of time and temperature on biochar properties. Biochar ash content, surface area, pH, C, N, base cations and electric conductivity (EC) were all increased in biochars generated at 500℃ compared to biochar generated at 300℃. In contrast, H and O concentrations and cationic exchange capacity (CEC) were less at 500℃ than 300℃. Furthermore, higher contents of CaCO3, SiO2 and KCl were detected by XRD and EDS analysis in biochars produced at higher compared to lower temperatures. FTIR spectra showed the formation of thermo-stable compounds in biochars generated at higher rather than lower temperatures. Potassium and phosphorus contents increased with increasing temperature while N content showed variability. This experiment indicated the suitable feedstocks and pyrolysis condition for biochar production and availability of nutrients for improving soil fertility and C sequestration.In the second experiment of this study, biochars produced from swine manure (SM), fruit peels (FP), Phragmites australis (PA) and Brassica rape (BR) were applied at different rates to a Psammaquent and a Plinthudult at 70% moisture. At incubation, available concentrations of K, Ca, Na, Mg, Al, Cr, Cu, Zn, Cd, Pb, Ni, Mn, Fe, B and Mo were analyzed to determine the influence of biochars on available elemental concentrations in treated soils. Both biochar type and application rates to soils significantly changed the available soil concentrations of elements, whereas Pb, Cd, Cu, Ni, Mn, Zn and Fe were significantly reduced in most biochar treatments to both soils and Mo, Cu and Zn increased in SM biochar treatments (3% biochar:soil weight (wt:wt). The available concentrations of minerals such as Na, Mg, K and Ca significantly increased in most biochar treatments, with the exceptions of Mg and Ca, which were reduced in the BR treatments.After 90 days of incubation, soil phospholipid fatty acid (PLFA) and chemical properties were measured. Feedstock, and biochar types and application rate significantly affected the soil microbial communities and chemical properties. In the Psammaquent, PLFAs derived from bacteria, fungi, actinomycetes, G+ve and G-ve bacteria and sulfate reducers were higher with FP biochar at 3% and 1% wt:wt, respectively, followed by SM at 1% and PA biochar at 3% wt:wt, compared to the control soil. The control soil also contained higher concentrations of certain iso:anteiso PLFAs, which are indicative of environmental stress, than did biochar treated soils. Protozoa PLFAs only increased in PA 3% and BR 1% wt:wt treatments to Psammaquent. Redundancy analysis illustrated the relationships between microbial communities and chemical properties within biochar types and addition rates to soil. The analysis indicated that different biochars induced different chemical changes such as increased pH, dissolved organic carbon (DOC) and total carbon (TOC) and nitrogen (N) in soil and changed the microbial community structure. These properties may be used as indicators of both soil improvement and C sequestration. In the Plinthudult, PLFAs derived from bacteria, fungi, actinomycetes, G+ve bacteria, F:B ratio, cyclo, iso, anteiso, iso:anteiso and sulfate reducers were higher with FP biochar at 3% and 1%(wt:wt) respectively, followed by SM at 1% and PA biochar at 3% wt:wt, than in the control soil. In this soil, the protozoal population was significantly changed in all biochar treatments to Plinthudult compared to control. The G-ve bacterial PLFAs concentrations reduced in all biochar treated Plinthudult compared to the control. The pH, K, dissolved organic carbon and total carbon concentration increased in all soils amended with biochar. The nitrate (NO3) concentration decreased in most biochars except the SM and FP biochar treatments. The RDA analysis showed that PLFAs from bacteria, protozoa, iso, G+ve, saturated, sulfate reducers, ante iso, monosaturated, and fungi showed positive correlation with pH, DON, NO3- and eN, and were higher in PA, FP1% and SM 3% biochar treatment. The PLFAs of G-ve, actinomycetes, cyclopropane, anaerobic bacteria, iso:anteiso, F:B,cy:pre, sat:mono were positively correlated with soil respiration and DOC and were higher in FP 3% biochar treatments and control soil. RDA analysis indicated that biochars change soil properties e.g DOC, N, C and microbial communities in Plinthudult.In the third experiment of this study wheat straw biochar at 3% (weight/weight) was applied, in a greenhouse experiment, to a Psammaquent and Plinthudult. The experiment investigated leaching and ammonium acetate extractable nutrients, crop yields and the microbial community structure at rice harvest, in these biochar amended soils compared to controls. The biochar addition to both soils increased the soil pH from 4.2 to 6.2 and 4.7 to 6.7, total nitrogen by 135 and 37%, and organic carbon by 90 and 80%, in the Psammaquent and Plinthudult, respectively compared to the control soils. The dissolved organic nitrogen was decreased by 24 and 15% and dissolved organic carbon by 40 and 44% in the Psammaquent and Plinthudult respectively, compared to their respective controls. The biochar decreased the concentrations of K leached by 24%, B by 25%, Cu by 80%, Mn by 37% and Zn by 33% in the Psammaquent and Al by 38%, B by 50%, Cu by 60%, Fe by 43%, Mn by 69% and Zn by 83% in the Plinthudult compared to the controls at harvest. The extractable concentrations of Ca of 38%, Na of 53% in the Psammaquent and Ca of 29%, Mg of 41%, Na of 150% and Zn of 300% in the Plinthudult were higher than the control. The extractable concentrations of Al of 22%, Cu of 45%, Mn of 22%, Mo of 65% and Zn of 62% in the Psammaquent and the Al concentrations of 37% and Mo of 45% in the Plinthudult were decreased in the biochar treated soils compared to the controls at harvest. The biochar addition to the two soils increased the uptake of nutrients by both rice straw and grain. Biochar addition also changed the microbial community structure in both rice soils by increasing pH, total organic C and dissolved organic C. The biochars may increase nutrient incorporation into the plant biomass or adsorb them onto the biochar surfaces, resulting in decreased nutrient loss, increased soil fertility and enhanced crop yields. |
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