Factors regulating interaction among inorganic nitrogen and phosphorus species, plant uptake, and relevant cycling genes in a weakly alkaline soil treated with biochar and inorganic fertilizer.

To highlight how biochar affects the interaction between inorganic nitrogen species (ammonium nitrogen, nitrate nitrogen, and nitrite nitrogen: NH4+-N, NO3¯-N, and NO2¯-N) and phosphorus species (calcium phosphate, iron phosphate, and aluminum phosphate: CaP, FeP and AlP) in soil and plant uptake of these nutrients, walnut shell (WS)- and corn cob (CC)-derived biochars (0.5 %, 1 %, 2 %, and 4 %, w/w) were added to a weakly alkaline soil, and then Chinese cabbages were planted. The results showed that the changes in soil inorganic nitrogen were related to biochar feedstock, pyrolysis temperature, and application rate. For soil under the active nitrification condition (dominant NO3¯-N), a significant decrease in the NH4+-N/NO3¯-N ratio after biochar addition indicates enhanced nitrification (excluding WS-derived biochars at 2 % and 4 %), which can be explained by the most positive response of ammonia-oxidizing archaeal amoA to biochar addition. The CC-derived biochar more effectively enhanced soil nitrification than WS-derived biochar did. The addition of 4 % of biochars significantly increased soil inorganic phosphorus, and the addition of CC-derived biochars more effectively increased Ca2P than WS-derived biochars. Biochars significantly decreased plant uptake of phosphorus, while generally had little influence on plant uptake of nitrogen. Interestingly, NO2¯-N in soil significantly positively correlated with total phosphorus in both soil and plant, and significantly negatively correlated with phoC, indicating that a certain degree of NO2¯-N accumulation in soil slightly facilitated plant uptake of phosphorus but inhibited phoC-harboring bacteria. The NO3¯-N in soil significantly positively correlated with Ca2P and Ca8P, while the NH4+-N/NO3¯-N ratio significantly negatively correlated with Ca10P and FeP, indicating that the enhanced nitrification seemed to facilitate the change in phosphorus to readly available ones. This study will help determine how to scientifically and rationally use biochar to regulate inorganic nitrogen and phosphorus species in soil and plant uptake of these nutrients.

Levels of persistent toxic substances in different biochars and their potential ecological risk assessment.

This study investigated the levels of persistent toxic substances, such as 16 polycyclic aromatic hydrocarbons (Σ16PAHs) and heavy metals (Cu, As, Cd, Zn, Pb, Ni, Mo, and Cr) in biochars produced from crop residues (walnut shell, corn cob, corn straw, rice straw, and rice husk) at different heat treatment temperatures (HTTs, 250, 400, and 600 °C). The levels of Σ16PAHs in different biochars were 0.47-7.11 mg kg-1, with naphthalene and phenanthrene contributing the most. The Σ16PAHs had the positive correlations with H/C and (O + N)/C, but had negative correlations with biochar surface areas. This finding indicates the increasing hydrophobic π-π interactions between the PAHs and the aromatic sheets of biochars and even the trapping of PAHs within the micropores with the increase of HTTs. The levels of heavy metals in rice residue-derived biochars were significantly higher than those in other biochars. The heavy metals had positive correlations with ash contents in the biochars, indicating the enrichment of heavy metals in the ash. The potential ecological risks of PAHs and heavy metals (dosage: 1%, w/w; frequency: 1) were minimal according to the risk quotient of negligible concentrations (RQNCs: 2.50-47.40, << 800) and maximum permissible concentrations (RQMPCs: 0.02-0.48, << 1) for PAHs and the potential ecological risk indexes (PERI: 0.01-0.28, << 150) for heavy metals.

Effect of biochar on the presence of nutrients and ryegrass growth in the soil from an abandoned indigenous coking site: The potential role of biochar in the revegetation of contaminated site.

Little is known regarding how biochars' feedstock and pyrolysis temperature affect soil function and plant growth. To address this gap in knowledge, 12 biochars (walnut shells, corn cobs, corn straws, and rice straws were separately pyrolyzed at 250, 400, and 600°C for 4h) were applied to soil from an indigenous coking site with application rate of 2.5% (w/w) in a pot experiment to determine the impact of biochar types on macro-nutrients (total and available N, P, and K) and ryegrass growth in the soil from an indigenous coking site. Generally, the total N, P, and K in the soil was not significantly different from that of the control group. However, biochars decreased the available N from 21.76mg·kg-1 for the control to 14.96mg·kg-1. Corn straw and rice straw biochars increased the available P from 2.14mg·kg-1 for the control to 28.35mg·kg-1, specifically at higher pyrolysis temperature, while walnut shell and corn cob biochars had little influence on it regardless of pyrolysis temperature. Biochars increased the available K from 173.58mg·kg-1 for the control to 355.64mg·kg-1, varying as their feedstocks of corn cob>rice straw>corn straw>walnut shell and increasing with the increase of pyrolysis temperature. Correlation analysis suggests that it is responsible for the competition of soluble cations from biochars with K for adsorption sites on the soil surface. Biochars increased the ryegrass biomass from 0.07g·pot-1 for the control to 0.16g·pot-1, with the generally most effective stimulation by biochars produced at 400°C. Ryegrass biomass had obviously positive correlation with available K, indicating its essential role in the growth of ryegrass in the studied soil.