Comparing combined application of biochar and nitrogen fertilizer in paddy and upland soils: Processes, enhancement strategies, and agricultural implications.

Recently, biochar and N fertilizers have been used to tackle low N use efficiency (NUE) in crops across diverse environmental conditions. The coupling of biochar and N fertilizer may impact crop N utilization through different pathways in various soil types. However, there is currently a lack of comprehensive assessment of how coupling effects specifically influence N utilization in paddy and upland crops. We conducted a meta-analysis of 175 peer-reviewed studies to assess the responses of soil properties and crop traits in paddy and upland fields under coupling effects. The results indicate that NUE (+26.1 %) and N uptake (+15.0 %) in paddy fields increase more than in upland fields (+23.7 % and +8.0 %, respectively), with the coupling effect providing NH4+ predominantly for rice and NO3- for upland crops. NH4+ increases in paddy fields (+6.9 %) but decreases in upland fields (-0.7 %), while microbial biomass carbon (MBC) decreases in paddy fields (-2.9 %) and increases in upland fields (+36.0 %). These findings suggest that coupling effects supply soil inorganic nutrients in paddies and affect microbes in uplands, thereby positively affecting crop N utilization. Specifically, the greatest increase in paddy crop yield and N use efficiency occurs when the ratio of N fertilizer to biochar exceeds 1.5 %, and in uplands, it manifests when applying 10-20 t·ha-1 of biochar and <150 kg·ha-1 N fertilizer. In conclusion, this meta-analysis explores the differential effects of biochar and N fertilizer coupling in different arable land types, offering novel insights into the utilization strategies of biochar in agricultural fields.

Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system.

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

Exploring site-specific N application rate to reduce N footprint and increase crop production for green manure-rice rotation system in southern China.

Milk vetch (Astragalus sinicus L.) is leguminous green manure (GM) which produces organic nitrogen (N) for subsequent crops and is widely planted and utilized to simultaneously reduce the use of synthetic N fertilizer and its environmental costs in rice systems. Determination of an optimal N application rate specific to the GM-rice system is challenging because of the large temporal and spatial variations in soil, climate, and field management conditions. To solve this problem, we developed a framework to explore the site-specific N application rate for the low-N footprint rice production system in southern China based on multi-site field experiments, farmer field survey, and process-based model (WHCNS_Rice, soil water heat carbon nitrogen simulator for rice). The results showed that a process-based model can explain >83.3% (p < 0.01) of the variation in rice yield, aboveground biomass, crop N uptake, and soil mineral N. Based on the scenario analysis of the tested WHCNS_Rice model, the simple regression equation was developed to implement site-specific N application rates that considered variations in GM biomass, soil, and climatic conditions. Simulation evaluation on nine provinces in southern China showed that the site-specific N application rate reduced regional synthetic N fertilizer input by 29.6 ± 17.8% and 65.3 ± 23.0% for single and early rice, respectively; decreased their total N footprints (NFs) by 23.4% and 49.3%, respectively; and without reduction in rice yield, compared with traditional farming N practices. The reduction in total NF was attributed to the reduced emissions from ammonia volatilization by 35.2%, N leaching by 28.4%, and N runoff by 32.7%. In this study, we suggested a low NF rice production system that can be obtained by combining GM with site-specific N application rate in southern China.

Biochar performance for preventing cadmium and arsenic accumulation, and the health risks associated with mustard (Brassica juncea) grown in co-contaminated soils.

Cadmium (Cd) and arsenic (As) in co-contaminated soil can enter the human body harming health via the food chain, such as vegetables. Biochar derived from waste has been used to reduce heavy metal uptake by plant, but long-term effects of biochar under Cd and As co-contaminated soil needs to be investigated. A following mustard (Brassica juncea) was grown on co-contaminated soil amended with different raw materials of biochar including biochars pyrolyzed by lignite coal (LCB), rice straw (RSB), silkworm excrement (SEB), and sugar refinery sludge (SSB). The results showed that compared to the control, Cd and As contents of mustard shoot in SSB treatment decreased by 45-49% and 19-37% in two growing seasons, respectively, which was the most effective among 4 biochars. This probably due to SSB owns more abundant Fe-O functional groups. Biochar also altered the microbial community composition, specifically SSB increased proteobacteria abundance by 50% and 80% in the first and second growing seasons, thereby promoted the simultaneous immobilization of Cd and As in soils which may reduce the potential risks to humans. In summary, considering the long-term effects and security of SSB application on mustard, not only is it an effective waste recycle option, but it should also be promoted as a promising approach for safe vegetable production in Cd and As co-contaminated soils.

Soil chemistry, metabarcoding, and metabolome analyses reveal that a sugarcane-Dictyophora indusiata intercropping system can enhance soil health by reducing soil nitrogen loss.

Introduction: Greater amounts of fertilizer are applied every year to meet the growing demand for food. Sugarcane is one of the important food sources for human beings. Methods: Here, we evaluated the effects of a sugarcane-Dictyophora indusiata (DI) intercropping system on soil health by conducting an experiment with three different treatments: (1) bagasse application (BAS process), (2) bagasse + DI (DIS process), and (3) the control (CK). We then analyzed soil chemistry, the diversity of soil bacteria and fungi, and the composition of metabolites to clarify the mechanism underlying the effects of this intercropping system on soil properties. Results and discussion: Soil chemistry analyses revealed that the content of several soil nutrients such as nitrogen (N) and phosphorus (P) was higher in the BAS process than in the CK. In the DIS process, a large amount of soil P was consumed by DI. At the same time, the urease activity was inhibited, thus slowing down the loss of soil in the DI process, while the activity of other enzymes such as ß-glucosidase and laccase was increased. It was also noticed that the content of lanthanum and calcium was higher in the BAS process than in the other treatments, and DI did not significantly alter the concentrations of these soil metal ions. Bacterial diversity was higher in the BAS process than in the other treatments, and fungal diversity was lower in the DIS process than in the other treatments. The soil metabolome analysis revealed that the abundance of carbohydrate metabolites was significantly lower in the BAS process than in the CK and the DIS process. The abundance of D(+)-talose was correlated with the content of soil nutrients. Path analysis revealed that the content of soil nutrients in the DIS process was mainly affected by fungi, bacteria, the soil metabolome, and soil enzyme activity. Our findings indicate that the sugarcane-DIS intercropping system can enhance soil health.

Research on the interaction of "tourism development-land use-landscape pattern" since the 1990s in a small karst basin, China.

The rapid rise of tourism in the karst regions has promoted the development of the local economy by relying on the unique landforms and landscapes. However, tourism development is often accompanied by land use changes and has an impact on the ecological environment. Exploring the coupling relationship between "tourism development-land use-landscape pattern" is very important for ecologically fragile karst areas. Taking the Yulong River Basin as an example, this research applied 3S technology, spatial analysis based on POIs, and regression analysis to the following: (1) identifying the process and effects of land use change, (2) determining the spatial pattern of tourism land and its correlation with land use change, (3) determining the characteristics and impacts of landscape pattern evolution. As the results suggested: (1) The significant expansion of construction land occupies a large amount of farmland, there is a balanced relationship between farmland and forest land for mutual conversion. (2) The aggregation of tourist land is affected by the trend of tourist behavior and the distribution of scenic spots. There is a significant moderate positive correlation between tourism land and construction land. (3) With the land use change, landscape heterogeneity has improved, but landscape fragmentation is serious and landscape connectivity is reduced. This research provides new evidences for the effect of the rapid development of tourism on land use change and ecological environment and as a reference to future orderly and moderate land development and ecological sustainability in karst regions.

Coupled mechanism of enhanced and inhibitory effects of nanoscale zero-valent iron on methane production and antibiotic resistance genes in anaerobic digestion of swine manure.

In this study, the turning point for nanoscale zero-valent iron's (NZVI) promotion and inhibition effects of methane production coupled with the reduction of antibiotic resistance genes (ARGs) was investigated. Adding 150 mmol/L NZVI increased methane production by maximum of 23.8 %, which was due to the chemical reaction producing H2 and enhancement of direct interspecies electron transfer (DIET) by NZVI. NZVI350 dramatically repressed methane generation by 48.0 %, which might be associated with the large quantity of reactive oxygen species (ROS) and excessive H2 inhibiting the functioning of microorganisms. The fate of ARGs was significantly related to daily methane production, indicating that the more methane production finally generated, the less the abundance of ARGs at last left. The reduction of ARGs was enhanced by maximum of 61.0 %, which was attributed to the inhibition of vertical gene transfer (VGT) and horizontal gene transfer (HGT) caused by steric hindrance associated with NZVI corrosion.

Acute toxicity of eucalyptus leachate tannins to zebrafish and the mitigation effect of Fe3+ on tannin toxicity.

Fish ponds polluted by the black water of eucalyptus forests (formed by the complexation of eucalyptus tannins with Fe3+) have experienced fish deaths. However, the toxicity of the components of black water is still unclear. To study the acute toxicities of eucalyptus leachate tannins to fish, their changes in the presence of Fe3+, and the underlying mechanisms, the static bioassay test method was adopted for acute exposure testing of zebrafish. Zebrafish were exposed to three kinds of tannins, namely, tannic acid (TA), epigallocatechin gallate (EGCG) and tannins from fresh eucalyptus leaf leacheate (TFL), and to solutions of these tannins with different molar ratios of Fe3+, under both no-aeration and aeration conditions. The results showed that the 48 h LC50 values of TA, EGCG and TFL were respectively 92, 47, and 186 mg·L-1, under no aeration, and 171, 86, and 452 mg·L-1 under aeration. When Fe3+ at 2, 1, and 6 times the molar amount of tannin was added to LC100 solutions of TA, EGCG and TFL, zebrafish mortality in 24 h was reduced to 0-33%. Acute fish death in eucalyptus plantation areas is related to high concentrations of eucalyptus tannins in the water. However, with increasing dissolved oxygen and Fe3+ levels, the acute toxicity of tannins to fish can be reduced. Thus, the black water in eucalyptus plantation areas reflects a water quality phenomenon that reduces the acute toxicity of eucalyptus tannins to fish. The mechanism of tannin toxicity to fish may be related to the impairment of oxygen delivery by fish blood, but the mechanism needs further study. These results provide a scientific basis for the prevention and control of fish suffering from acute eucalyptus tannin poisoning in eucalyptus plantation areas and for the protection of water resources.

Response of soil microbial communities and rice yield to nitrogen reduction with green manure application in karst paddy areas.

Fertilizer application practices are one of the major challenges facing agroecology. The agrobenefits of combined application of green manure and chemical fertilizers, and the potential of green manure to replace chemical fertilizers are now well documented. However, little is known about the impact of fertilization practices on microbial communities and tice yield. In this study, the diversity of bacterial and fungal communities, symbiotic networks and their relationship with soil function were analyzed in five fertilization treatments (N: 100% nitrogen fertilizer alone; M: green manure alone; MN60: green manure couple with 60% nitrogen fertilizer, MN80: green manure couple with 80% nitrogen fertilizer; and MN100: green manure couple with 100% nitrogen fertilizer). First, early rice yield was significantly higher by 12.6% in MN100 treatment in 2021 compared with N. Secondly, soil bacterial diversity showed an increasing trend with increasing N fertilizer application after green manure input, however, the opposite was true for fungal diversity. Microbial interaction analysis showed that different fertilizer applications changed soil microbial network complexity and fertilizer-induced changes in soil microbial interactions were closely related to soil environmental changes. Random forest models further predicted the importance of soil environment, microorganisms and rice yield. Overall, nitrogen fertilizer green manure altered rice yield due to its effects on soil environment and microbial communities. In the case of combined green manure and N fertilizer application, bacteria and fungi showed different responses to fertilization method, and the full amount of N fertilizer in combination with green manure reduced the complexity of soil microbial network. In contrast, for more ecologically sensitive karst areas, we recommend fertilization practices with reduced N by 20-40% for rice production. Graphical Abstract.