Effects of solid waste-based soil conditioner and arbuscular mycorrhizal fungi on crop productivity and heavy metal distribution in foxtail millet (Setaria italica).

Shanxi is a large coal-producing province, and it also produces a lot of solid waste. Solid waste can leach heavy metals, which can harm soil and affect food security at the beginning of the food chain. To investigate the impacts of solid waste-based soil conditioner (SWSC) and arbuscular mycorrhizal fungi (AMF) on millet safety and crop production, a field experiment with foxtail millet (Setaria italica) was conducted in Tunliu. The results of this study demonstrate that SWSC + AMF, SWSC and AMF can increase millet yield by 28.0%, 27.1% and 19.5%, respectively, compared with CK. This is mainly due to increased mycorrhizal infection. Besides, the pollution index (Pi) and the Nemerow-integrated pollution index (PN) of the soil with SWSC and AMF were both below 0.7, indicating safe pollution levels. The application of AMF and SWSC inhibits plants from absorbing heavy metals from the soil and reduces the TFroot/soil of the millet. SWSC + AMF application inhibited the transfer of heavy metals from the roots to the upper part of the ground and reduced the TFshoot/root of the millet. The TFgrain/soil of the millet was below 1. The HQ and HI of the millet grains did not exceed 1, indicating the absence of a potential health risk. Therefore, SWSC combined with AMF is applicable for millet production in Tunliu, and the combined treatment can decrease heavy metal phytoavailability and post-harvest transfer risks. This work provides a way to utilize solid waste while also improving millet yields in dry farming. Based on the review, we suggested future researches to better understand the mechanisms of SWSC + AMF long-term application to promote awareness on its role over time through alterations in its surface chemistry, soil microbial community and environmental implications.

Effects of different modifiers on the sorption and structural properties of biochar derived from wheat stalk.

Nitrobenzene is a widespread contaminant in water. Biochar (BC) is a promising material for removing organic pollutants, but the adsorption capacity of pristine BC is low. Chemical modification is often used to improve the adsorption performance, but information on the sorption of nitrobenzene by modified BC is rare. In this study, BCs pyrolyzed at 300, 500, and 700 °C were modified by hydrochloric acid (HCl), sulfuric acid (H2SO4), sodium hydroxide (NaOH), hydrogen peroxide (H2O2), and nitric acid (HNO3), respectively. The properties, nitrobenzene sorption behaviors, and sorption mechanisms of different BCs were analyzed. The results showed that chemical modification decreased the sorption of nitrobenzene on BCs pyrolyzed at 300 °C, possibly due to the loss of the partition phase and the increase in polarity after modification. Regarding BCs pyrolyzed at 500 and 700 °C, the NaOH and HCl modifications significantly increased the sorption capacity by 19% and 60%, 18%, and 41%, respectively, possibly due to the increase in surface area, available pores, and aromaticity, while HNO3 modification decreased the sorption capacity by 41% and 31%. Two reasons were probably responsible for the decrease: one was the decrease in surface area after HNO3 modification due to the destruction of pore walls and the continuity of holes; the other was the strong repulsion between the nitro groups formed on the surface of BC and the nitro groups of nitrobenzene that drove nitrobenzene molecules away from the surface. A principal component-based comprehensive evaluation of the BC properties, which were significantly correlated with the sorption isotherm parameters, was used to evaluate the nitrobenzene sorption performance of the modified BC. Overall, BC pyrolyzed at 700 °C modified with NaOH or HCl were proposed as effective sorption materials for the removal of nitrobenzene in environment, which also provided a chemical modified method of biochar derived from agricultural waste.

Biochar induced changes of soil dissolved organic matter: The release and adsorption of dissolved organic matter by biochar and soil.

Dissolved organic matter (DOM) is an important organic matter fraction that affects many biological and chemical processes in soil. Biochar can change soil DOM while the effects were paradoxical, and contributions of biochar to soil DOM was not clear yet. In this study, excitation-emission matrix (EEM) fluorescence spectroscopy was applied to determine the biochar-induced changes of DOM composition. Batch experiments were conducted to quantify the contributions of biochar to soil DOM. Biochars were prepared by pyrolyzing wheat straw (S300/700) and cow manure (M300/700) at 300 and 700 °C, respectively. Generally, biochar increased the humification of soil DOM possibly by the release of indigenous DOM and selective adsorption of the small molecule DOM. Besides, contributions of S300 and M300 to soil DOM (37-91%) were higher than that of S700 and M700 (2-19%) irrespective of application rates. The indigenous DOM released from S300 and M300 was 6.4-12.1 times more than the soil DOM adsorbed by S300 and M300, leading to the increase of DOM content. Contrarily, the DOM from S700 and M700 was only 11-17% of the soil DOM adsorbed by them, resulting in the decrease of DOM content. In addition, contributions of biochar to soil DOM increased as the application rate increased, especially for S300 and M300. This study indicated that the release and adsorption of DOM were the key processes determining the effects of biochar on soil DOM, which were closely related to the pyrolysis temperature and application rate of biochar.

Preparation of Ultrafine Fly Ash-Based Superhydrophobic Composite Coating and Its Application to Foam Concrete.

The waterproof and thermal insulation property of foamed concrete is very important. In this study, the ultrafine fly ash (UFA)-based superhydrophobic composite coating was applied onto foam concrete. The UFA-based base coating that closely adhered to the concrete initially improved the waterproofness of the test block, and the silane coupling agent-modified UFA-based surface coating further achieved superhydrophobicity. The UFA on the coating surface and the asperities on the surface jointly formed a lotus leaf-like rough micro-nanostructure. The 154.34° water drop contact angle and 2.41° sliding angle on No. 5 coating were reached, indicating that it was a superhydrophobic surface. The water absorption ratios of the composite coating block were 1.87% and 16.6% at 4 h and 7 days, which were reduced by 97% and 75% in comparison with the original foam concrete. The compressive strength and heat conductivity coefficient after soaking for 4 h of the composite coating block were higher than 4.0 MPa and 0.225 W·m-1·K-1, respectively. The UFA-based superhydrophobic composite coating proposed in this study and applied onto foam concrete is simple and cheap, requires no precise instrument, and can be applied in a large area.

Separated pathways for biochar to affect soil N2O emission under different moisture contents.

Dry land is a massive contributor to global nitrous oxide (N2O) production and biochar is a potential material for soil amendment that can impact soil N2O emission. Considering that the moisture content of dry land is usually changeable, it is essential to investigate the effect of biochar on soil N2O emission under different moisture contents. Therefore, column experiments were conducted with two biochars (B300 and B500, biochars pyrolyzed at 300 and 500 °C, respectively) under five moisture contents (18%, 21%, 24%, 27% and 30%, w/w). The results showed that B300 promoted N2O emission under the moisture contents of 18%, 21% and 24% by increasing the content of dissolved organic carbon and thus enhancing the microbial processes related to N2O production. However, when the moisture contents were 27% and 30%, the promotion of N2O production was overwhelmed by the improvement in N2O reduction due to the B300 induced increase in the abundance ratio of nosZ to nirS, leading to the decrease in N2O emission. Moreover, B500 did not alter the content of dissolved organic matter significantly and thus caused no significant change in N2O emission when the moisture contents were 18%, 21% and 24%. But it was able to increase the abundance ratio of nosZ to nirS and thus decrease N2O emission when the moisture contents were 27% and 30%. The results further clarified the effect of biochar on soil N2O emission and helped to evaluate the N2O-suppressing-potential of biochar.

Impact of biochar on soil N2O emissions under different biochar-carbon/fertilizer-nitrogen ratios at a constant moisture condition on a silt loam soil.

Biochar amendment has been proposed as a potential solution for improving soil quality and suppressing greenhouse gas emission. Considering the serious nitrogen fertilizer overuse problem in China, it is important to investigate the effect of biochar on soil with excess nitrogen fertilizer. Therefore, two sets of soil column experiments were conducted to explore the effect of biochar on N2O emission from nitrogen fertilizer-overused soil. Three types of biochar (biochars pyrolzed at 300, 500 and 700°C, respectively) and one type of nitrogen fertilizer (ammonium sulfate) were investigated at varying application rates. It was found that N2O emission was related to both biochar and N-fertilizer application rates, and increased N2O emission was negatively correlated with the TC/IN ratio (the ratio of total carbon to inorganic nitrogen) after biochar application. The soil TC/IN ratio determined the ammonium utilization pathway, affecting the intensity of nitrification and N2O emission. When the TC/IN ratio was relatively high (>60), suppressed nitrification led to the suppression of N2O emission. Conversely, enhanced nitrification when the TC/IN ratio was relatively low (<45) caused the promotion of N2O emission. In conclusion, biochar's suppression of soil N2O emission was conditional and biochar should be applied in a proper ratio to nitrogen fertilizer to avoid excessive N2O emission.