Response of soil carbon dioxide fluxes,soil organic carbon and microbial biomass carbon to biochar amendment: a meta‐analysis

Biochar as a carbon‐rich coproduct of pyrolyzing biomass, its amendment has been advocated as a potential strategy to soil carbon (C) sequestration. Updated data derived from 50 papers with 395 paired observations were reviewed using meta‐analysis procedures to examine responses of soil carbon dioxide (CO₂) fluxes, soil organic C (SOC), and soil microbial biomass C (MBC) contents to biochar amendment. When averaged across all studies, biochar amendment had no significant effect on soil CO₂ fluxes, but it significantly enhanced SOC content by 40% and MBC content by 18%. A positive response of soil CO₂ fluxes to biochar amendment was found in rice paddies, laboratory incubation studies, soils without vegetation, and unfertilized soils. Biochar amendment significantly increased soil MBC content in field studies, N‐fertilized soils, and soils with vegetation. Enhancement of SOC content following biochar amendment was the greatest in rice paddies among different land‐use types. Responses of soil CO₂ fluxes and MBC to biochar amendment varied with soil texture and pH. The use of biochar in combination with synthetic N fertilizer and waste compost fertilizer led to the greatest increases in soil CO₂ fluxes and MBC content, respectively. Both soil CO₂ fluxes and MBC responses to biochar amendment decreased with biochar application rate, pyrolysis temperature, or C/N ratio of biochar, while each increased SOC content enhancement. Among different biochar feedstock sources, positive responses of soil CO₂ fluxes and MBC were the highest for manure and crop residue feedstock sources, respectively. Soil CO₂ flux responses to biochar amendment decreased with pH of biochar, while biochars with pH of 8.1–9.0 had the greatest enhancement of SOC and MBC contents. Therefore, soil properties, land‐use type, agricultural practice, and biochar characteristics should be taken into account to assess the practical potential of biochar for mitigating climate change.     

Soil biochemical properties and crop productivity following application of locally produced biochar at organic farms on Waldron Island,WA

Biochar (a carbon-rich product from pyrolysis of organic materials) additions to agricultural soils have been shown to often result in neutral to positive influences on soil properties and processes; however, the only a limited number of studies have been conducted on active organic farming systems and of those, none have used multivariate analytical methods to examine the influence of biochar on soil microbial activity, nutrient cycling, and crop performance. In this study, biochar produced from local timber harvest residues on Waldron Island, WA was applied in factorial combination with a poultry litter based fertilizer to replicated plots on six organic farms that were all growing Kabocha squash (Cucurbita maxima) in the summer of 2016. A series of soil physicochemical and biochemical properties were examined after 5 months of biochar application; squash samples were evaluated for productivity and nutrient uptake. Factorial multivariate analysis of variance (MANOVA) revealed a significant influence of biochar on soil properties as well as a synergistic effect of biochar and poultry litter during a 5 month field trial. Principle component analysis (PCA) highlighted soil total C content, microbial biomass C, enzyme activities, bioavailable P, and phosphatase enzyme activity as the variables most influenced by biochar incorporation into surface mineral soil. Redundancy analysis (RDA) further indicated that better soil biochemical conditions, particularly soil enzyme activities and available P concentrations, were associated with higher crop productivity in biochar-treated plots. Overall, our study demonstrates that locally produced wood biochar, in addition to improving soil C storage, has the potential to significantly improve soil fertility and crop productivity in organic farming systems on sandy soils.     

Effects of biochar application on soil greenhouse gas fluxes: a meta‐analysis

Biochar application to soils may increase carbon (C) sequestration due to the inputs of recalcitrant organic C. However, the effects of biochar application on the soil greenhouse gas (GHG) fluxes appear variable among many case studies; therefore, the efficacy of biochar as a carbon sequestration agent for climate change mitigation remains uncertain. We performed a meta‐analysis of 91 published papers with 552 paired comparisons to obtain a central tendency of three main GHG fluxes (i.e., CO₂, CH₄, and N₂O) in response to biochar application. Our results showed that biochar application significantly increased soil CO₂ fluxes by 22.14%, but decreased N₂O fluxes by 30.92% and did not affect CH₄ fluxes. As a consequence, biochar application may significantly contribute to an increased global warming potential (GWP) of total soil GHG fluxes due to the large stimulation of CO₂ fluxes. However, soil CO₂ fluxes were suppressed when biochar was added to fertilized soils, indicating that biochar application is unlikely to stimulate CO₂ fluxes in the agriculture sector, in which N fertilizer inputs are common. Responses of soil GHG fluxes mainly varied with biochar feedstock source and soil texture and the pyrolysis temperature of biochar. Soil and biochar pH, biochar applied rate, and latitude also influence soil GHG fluxes, but to a more limited extent. Our findings provide a scientific basis for developing more rational strategies toward widespread adoption of biochar as a soil amendment for climate change mitigation.     

Soil carbon increased by twice the amount of biochar carbon applied after 6 years: Field evidence of negative priming

Applying biochar to agricultural soils has been proposed as a means of sequestering carbon (C) while simultaneously enhancing soil health and agricultural sustainability. However, our understanding of the long‐term effects of biochar and annual versus perennial cropping systems and their interactions on soil properties under field conditions is limited. We quantified changes in soil C concentration and stocks, and other soil properties 6 years after biochar applications to corn (Zea mays L.) and dedicated bioenergy crops on a Midwestern US soil. Treatments were as follows: no‐till continuous corn, Liberty switchgrass (Panicum virgatum L.), and low‐diversity prairie grasses, 45% big bluestem (Andropogon gerardii), 45% Indiangrass (Sorghastrum nutans), and 10% sideoats grama (Bouteloua curtipendula), as main plots, and wood biochar (9.3 Mg/ha with 63% total C) and no biochar applications as subplots. Biochar‐amended plots accumulated more C (14.07 Mg soil C/ha vs. 2.25 Mg soil C/ha) than non‐biochar‐amended plots in the 0–30 cm soil depth but other soil properties were not significantly affected by the biochar amendments. The total increase in C stocks in the biochar‐amended plots was nearly twice (14.07 Mg soil C/ha) the amount of C added with biochar 6 years earlier (7.25 Mg biochar C/ha), suggesting a negative priming effect of biochar on formation and/or mineralization of native soil organic C. Dedicated bioenergy crops increased soil C concentration by 79% and improved both aggregation and plant available water in the 0–5 cm soil depth. Biochar did not interact with the cropping systems. Overall, biochar has the potential to increase soil C stocks both directly and through negative priming, but, in this study, it had limited effects on other soil properties after 6 years.     

生物炭对不同土壤化学性质、小麦和糜子产量的影响

以小麦和糜子为供试作物,利用室外盆栽试验,研究了不同添加量生物炭与矿质肥配施对两种不同土壤化学性质及小麦和糜子产量的影响。生物炭当季用量设5个水平：B0 (0 t/hm2)、B5 (5 t/hm2)、B10 (10 t/hm2)、B15 (15 t/hm2)和B20 (20 t/hm2),氮磷钾肥均作基肥施用。结果表明：1.与对照相比,施用生物炭可以显著增加新积土糜子季土壤pH值,其他处理随生物炭用量的增加虽有增加趋势但差异不显著;显著增加新积土土壤阳离子交换量,增幅为1.5 %—58.2 %;显著增加两种土壤有机碳含量,增幅为31.1 %—272.2 %;2.两种土壤的矿质态氮含量、新积土土壤有效磷和速效钾含量随生物炭用量的增加而显著提高,氮磷钾增幅分别为6.0 %—112.8 %、3.8 %—38.5 %和6.1 %—47.2 %;3.生物炭可显著提高塿土上作物氮吸收量,而作物磷、钾吸收量虽有增加,但差异不显著。生物炭对小麦和糜子的增产效应尚不稳定,在试验最高用量时甚至产生轻微抑制作用。总之,施用生物炭在一定程度上可以改善土壤化学性质,提高土壤有效养分含量,但生物炭对土壤和作物的影响与土壤、作物类型及土壤肥力密切相关。     

生物质炭添加对红壤性水稻土重金属有效性及土壤质量的影响

通过田间定位试验探讨了不同生物质炭添加量对红壤性水稻土理化性质、重金属有效性和土壤质量的影响。生物质炭于2017年水稻种植前一次性添加于耕作层(0~17cm),分别设置5个不同处理:CK:0 t·hm^-2,A10:10 t·hm^-2,A20:20 t·hm^-2,A30:30t·hm^-2和A40:40 t·hm^-2,经种植两季水稻后于2018年9月采集耕作层(0~17 cm)和犁底层(17~29 cm)土壤,计算土壤质量指数(SQI),评价土壤质量。结果表明:在耕作层(0~17 cm)和犁底层(17~29 cm),随着生物质炭添加量的增加,土壤容重逐渐降低;土壤孔隙度、pH值、有机质和可溶性有机碳含量增加,铵态氮和有效磷分别在添加量为20和30 t·hm^-2时达到最大值;土壤中脲酶、过氧化氢酶和蔗糖酶的活性降低;生物质炭能够降低有效态Cd、As和Pb的含量,在生物质炭添加量为40 t·hm^-2时最低;在土壤耕作层(0~17cm),有效态Cd、As和Pb含量分别与脲酶、土壤pH值和蔗糖酶呈显著线性相关;在土壤犁底层(17~29 cm),有效态Cd、As和Pb含量分别与脲酶、过氧化氢酶和有效磷含量呈显著线性相关;各处理的SQI由高到低依次为A40>A30>A20>A10>CK,对应的指数值分别为0.641、0.638、0.579、0.533和0.464。这表明,红壤性水稻土的土壤质量在生物质炭添加量为40 t·hm^-2时,达到最佳。综上所述,生物质炭在添加第二年后,能够显著降低红壤性水稻土的有效态重金属含量,提高土壤质量。     

生物炭对农田土壤微生物生态的影响研究进展

生物炭作为新型土壤改良剂在国内外环境科学等领域受到广泛的关注.关于生物炭对土壤理化性质的改良研究较早,目前虽然已深入到土壤微生物生态的领域,但是大多数将土壤理化性质与土壤微生物生态分开考虑,缺乏对二者相互作用的系统评述.本文总结了施用生物炭后土壤理化性质的改变与土壤微生物群落变化之间的相互关系:生物炭不仅能够提高土壤pH值、增强土壤的持水能力、增加土壤有机质等,而且会影响土壤微生物的群落结构、改变细菌和真菌的丰度;施用生物炭后,土壤环境和土壤微生物之间互相影响互相制约,共同促进了土壤微生物生态系统的改良.本文旨在为生物炭改良农田土壤微生态的深入研究提供新的思路,从生态系统的角度促进生物炭环境效应影响的研究,使生物炭的应用更具有科学性和有效性,并对生物炭在相关领域的应用进行了展望.     

Functional response of the soil microbial community to biochar applications

Biochar has the potential to mitigate the impacts of climate change and soil degradation by simultaneously sequestering C in soil and improving soil quality. However, the mechanism of biochar's effect on soil microbial communities remains unclear. Therefore, we conducted a global meta‐analysis, where we collected 2,110 paired observations from 107 published papers and used structural equation modeling (SEM) to analyze the effects of biochar on microbial community structure and function. Our result indicated that arbuscular mycorrhizal fungal abundance, microbial biomass C, and functional richness increased with biochar addition regardless of loads, time since application, and experiment types. Results from mixed linear model analysis suggested that soil respiration and actinomycetes (ACT) abundance decreased with biochar application. With the increase of soil pH, the effect of biochar on fungal abundance and C metabolic ability was lessened. Higher biochar pH associated with higher pyrolysis temperatures reduced the abundance of bacteria, fungi, ACT, and soil microbes feeding on miscellaneous C from Biolog Eco‐plate experiments. SEM that examined the effect of biochar properties, load, and soil properties on microbial community indicated that fungal abundance was the dominant factor affecting the response of the bacterial abundance to biochar. The response of bacterial abundance to biochar addition was soil dependent, whereas fungi abundance was mostly related to biochar load and pyrolysis temperature. Based on soil conditions, controlling biochar load and production conditions would be a direct way to regulate the effect of biochar application on soil microbial function and increase the capacity to sequester C.     

Influence of Willow Biochar Amendment on Soil Nitrogen Availability and Greenhouse Gas Production in Two Fertilized Temperate Prairie Soils

The potential of biochar to improve numerous soil physical, chemical and biological properties is well known. However, previous research has concentrated on old and highly weathered tropical soils with poor fertility, while reports regarding the influence of biochar application on relatively young and fertile temperate prairie soils are limited. Furthermore, the mechanism(s) underlying biochar-induced effects on the plant availability of inorganic nitrogen (N) fertilizers and their relationship to greenhouse gas production is not well understood. The objective of this study was to determine the effect of a biochar soil amendment, produced by slow pyrolysis using shrub willow (Salix spp.) bioenergy feedstock, on CO₂, N₂O and CH₄ fluxes by two contrasting marginal soils from Saskatchewan, Canada with and without added urea, over a 6-week incubation period. Biochar decreased soil N availability after 6 weeks only in the lower organic matter (Brown) soil, with no effect on the Black soil, regardless of fertilizer N addition, which was attributed to soil N immobilization by heterotrophs mineralizing the labile biochar-carbon. There appeared to be a synergistic effect when combining biochar and urea, evidenced by enhanced urease activity and higher initial nitrification rates compared to biochar or fertilization alone. The accelerated urea hydrolysis in the presence of biochar may increase NH₃ volatilization losses associated with urea fertilization and, therefore, warrants further investigation. The decreased N₂O emissions following biochar addition, with (both soils) or without (Black soil) fertilizer N, could be due to decreased ammonium and nitrate availability, along with changes in denitrification potential as related to improved aeration. Biochar significantly reduced the water-filled pore space, which concurrently increased CH₄ consumption in both soils. The lack of biochar effect on CO₂ emissions from either soil, with or without fertilizer N, suggests enhanced CO₂ consumption by autotrophic nitrifiers. Biochar application appears to be an effective management approach for improving N₂O and CH₄ fluxes in temperate prairie soils.     

The effect of biochar management on soil and plant community properties in a boreal forest

Biochar management has been proposed as a possible tool to mitigate anthropogenic CO₂ emissions, and thus far its impacts in forested environments remain poorly understood. We conducted a large‐scale, replicated field experiment using 0.05‐ha plots in the boreal region in northern Sweden to evaluate how soil and vegetation properties and processes responded to biochar application and the disturbance associated with burying biochar in the soil. We employed a randomized block design, where biochar and soil mixing treatments were established in factorial combination (i.e., control, soil mixing only, biochar only, and biochar and soil mixing; n = 6 plots of each). After two growing seasons, we found that biochar application enhanced net soil N mineralization rates and soil concentrations regardless of the soil mixing treatment, but had no impact on the availability of , the majority of soil microbial community parameters, or soil respiration. Meanwhile, soil mixing enhanced soil concentrations, but had negative impacts on net N mineralization rates and several soil microbial community variables. Many of the effects of soil mixing on soil nutrient and microbial community properties were less extreme when biochar was also added. Biochar addition had almost no effects on vegetation properties (except for a small reduction in species richness of the ground layer vegetation), while soil mixing caused significant reductions in graminoid and total ground layer vegetation cover, and enhanced seedling survival rates of P. sylvestris, and seed germination rates for four tree species. Our results suggest that biochar application can serve as an effective tool to store soil C in boreal forests while enhancing availability. They also suggest that biochar may serve as a useful complement to site preparation techniques that are frequently used in the boreal region, by enhancing soil fertility and reducing nutrient losses when soils are scarified during site preparation.     

Biochar – synergies and trade‐offs between soil enhancing properties and C sequestration potential

The characterization of biochar has been predominantly focused around determining physicochemical properties including chemical composition, porosity and volatile content. To date, little systematic research has been done into assessing the properties of biochar that directly relate to its function in soil and how production conditions could impact these. The aim of this study was to evaluate how pyrolysis conditions can influence biochar's potential for soil enhancing benefits by addressing key soil constraints, and identify potential synergies and restrictions. To do this, biochar produced from pine wood chips (PC), wheat straw (WS) and wheat straw pellets (WSP) at four highest treatment temperatures (HTT) (350, 450, 550 and 650 °C) and two heating rates (5 and 100 °C min^?1) were analysed for pH, extractable nutrients, cation exchange capacity (CEC), stable‐C content and labile‐C content. Highest treatment temperature and feedstock selection played an important role in the development of biochar functional properties while overall heating rate (in the range investigated) was found to have no significant effect on pH, stable‐C or labile‐C concentrations. Increasing the HTT reduced biochar yield and labile‐C content while increasing the yield of stable‐C present within biochar. Biochar produced at higher HTT also demonstrated a higher degree of alkalinity improving biochar's ability to increase soil pH. The concentration of extractable nutrients was mainly affected by feedstock selection while the biochar CEC was influenced by HTT, generally reaching its highest values between 450–550 °C. Biochar produced at ≥550 °C showed high combined values for C stability, pH and CEC while lower HTTs favoured nutrient availability. Therefore attempts to maximize biochar's C sequestration potential could reduce the availability of biochar nutrients. Developing our understanding of how feedstock selection and processing conditions influence key biochar properties can be used to refine the pyrolysis process and design of ‘bespoke biochar’ engineered to deliver specific environmental functions.     

不同磷水平配施生物炭对土壤磷有效性

生物炭在提高土壤磷素有效性及促进作物生长方面具有显著作用,但其效果因土壤类型不同存在较大差异。试验以赤红壤(pH 4.91)和褐土(pH 7.24)为供试土壤,设置3种磷肥水平(0、30、90 kg P·hm^-2,分别以不施磷、低磷、高磷表示)配施稻秆生物炭(0、4%)的大豆盆栽试验,研究了不同磷水平下配施生物炭对土壤磷有效性、磷酸单酯酶活性和植株磷吸收的影响。结果表明: 不同磷水平配施生物炭显著提高了两种土壤的速效磷和全磷含量,且低磷水平添加生物炭处理速效磷增幅最大,在赤红壤和褐土的增幅分别为192.6%和237.1%。与低磷相比,赤红壤中低磷配施生物炭处理的碱性磷酸单酯酶活性显著增加78.9%,活性有机磷含量降低39.3%,同时显著促进了植株生长与磷吸收;生物炭添加显著降低了褐土活性有机磷含量,但不同处理对土壤磷酸单酯酶活性和植株生长无显著影响。土壤活性有机磷含量与速效磷含量均呈显著负相关。综上,生物炭对土壤磷有效性的作用因土壤类型和磷肥水平差异而不同,其在赤红壤上对植株生长和磷吸收的促进效应强于褐土,且在低磷条件下效果更佳。本研究为生物炭在减施磷肥和促进大豆磷吸收,特别是在赤红壤上的应用提供了科学依据。     

Biochar alters the soil microbiome and soil function: results of next‐generation amplicon sequencing across Europe

Wide‐scale application of biochar to soil has been suggested as a mechanism to offset increases in CO₂ emissions through the long‐term sequestration of a carbon rich and inert substance to the soil, but the implications of this for soil diversity and function remain to be determined. Biochar is capable of inducing changes in soil bacterial communities, but the exact impacts of its application are poorly understood. Using three European sites [UK SRC, short rotation coppice, French grassland (FR) and Italian SRF, short rotation forestry (IT)] treated with identical biochar applications, we undertook 16S and ITS amplicon DNA sequencing. In addition, we carried out assessments of community change over time and N and P mobilization in the UK. Significant changes in bacterial and community structure occurred due to treatment, although the nature of the changes varied by site. STAMP differential abundance analysis showed enrichment of Gemmatimonadete and Acidobacteria in UK biochar plots 1 year after application, whilst control plots exhibited enriched Gemmataceae, Isosphaeraceae and Koribacteraceae. Increased mobility of ammonium and phosphates was also detected after 1 year, coupled with a shift from acid to alkaline phosphomonoesterase activity, which may suggest an ecological and functional shift towards a more copiotrophic ecology. Italy also exhibited enrichments, in both the Proteobacteria (driven by an increase in the order Rhizobiales) and the Gemmatimonadetes. No significant change in the abundance of individual taxa was noted in FR, although a small significant change in unweighted UNIFRAC occurred, indicating variation in the identities of taxa present due to treatment. Fungal β diversity was affected by treatment in IT and FR, but was unaffected in UK samples. The effects of time and site were greater than that of biochar application in UK samples. Overall, this report gives a tantalizing view of the soil microbiome at several sites across Europe and suggests that although application of biochar has significant effects on microbial communities, these may be small compared with the highly variable soil microbiome that is found in different soils and changes with time.     

Comparative efficiency of wheat straw and sugarcane bagasse biochar reduces the cadmium bioavailability to spinach and enhances the microbial activity in contaminated soil

Abstract

Biochar is considered a novel soil amendment for cadmium (Cd) stabilization in contaminated soils. A pot experiment was conducted to examine the efficiency of wheat straw and sugarcane bagasse induced biochar on Cd mobility in soil and its bioavailability to spinach in contaminated soil. Soil pH, Cd contents in plant tissues and microbial biomass were examined. Results showed that Cd was significantly decreased by 30.95% and 20.83% with wheat straw and sugarcane bagasse biochar at 2% application rate respectively, relative to the control. Similarly, Cd contents were decreased in plants shoots by 15.41 and 14.33%, while in roots by 48.3 and 35.54%, when wheat straw and sugarcane biochar were added at 2% application rate respectively. Moreover, soil microbial biomass was significantly increased with the application of all biochar types and their applications rates. Finally, wheat straw biochar at 2% application rate can be considered as an effective approach for Cd stabilization in contaminated soils.     

Chloropicrin Emission Reduction by Soil Amendment with Biochar

Biochar has sorption capacity, and can be used to enhance the sequestration of volatile organic contaminants such as pesticides in soil. Chloropicrin (CP) is an important soil fumigant for the production of many fruit and vegetable crops, but its emissions must be minimized to reduce exposure risks and air pollution. The objective of this study was to determine the capacity of biochar to adsorb CP and the effect of biochar amendments to soil on CP emission, concentration in the soil gas phase, degradation in soil and CP bioactivity for controlling soil borne pests. CP emission and concentration in the soil air phase were measured from packed soil columns after fumigant injection at 20-cm depth and application of selected doses of biocharto the surface 5 cm soil. Laboratory incubation and fumigation experiments were conducted to determine the capacity of biochar to adsorb CP, the effects on CP degradation and, separately, CP’s bioactivity on soil borne pests in soil amended with biochar. Biochar amendment at 2% to 5% (w/w) greatly reduced total CP emission losses by 85.7% - 97.7% compared to fumigation without biochar. CP concentrations in the soil gas-phase, especially in the top 5 cm of soil, were reduced within 48 h following application. The half-life of CP decreased from 13.6 h to 6.4 h as the biochar rate increased from 0% to 5%. CP and its metabolite (dichloronitromethane) both degraded more rapidly in pure biochar than in soil. The biochar used in the present study had a maximum adsorption capacity for CP of less than 5 mg g^-1. There were no negative effects on pathogen and nematode control when the biochar used in this study was less than 1% (on a weight basis) in soil. Biochar amendment to soil reduced the emissions of CP. CP concentrations in the top 5 cm of soil gas-phase were reduced. CP degradation was accelerated with the addition of biochar. The biochar used in the present study had a low adsorption capacity for CP. There were no negative effects on pathogen and nematode control when the biochar amendment rate was less than 1% (by weight). The findings would be useful for establishing guidelines for biochar use in soil fumigation.     

Interactive effects of biochar and an organic dust suppressant for revegetation and erosion control with herbaceous seed mixtures and willow cuttings

Land reclamation efforts on “non‐soil” substrates frequently involve additions of organic material coupled with soil‐stabilizing dust suppressants to control erosion, but formal experiments, particularly of interactive effects, are lacking. We examined the effects of Entac?, a tall oil pitch emulsion, and pyrolyzed wood waste‐derived biochar on early plant establishment, growth, and survivorship, in 2 factorial greenhouse experiments: 1 using a seed mix widely used for roadside erosion control (the grasses Festuca rubra, Poa pratensis, Lolium perenne, and white clover [Trifolium repens]) and 1 using rooted cuttings of sand bar willow (Salix exigua). Biochar additions of 5, 10, and 20 t/ha enhanced biomass of clover by 14–250%, but had no significant effects on grasses. Entac additions inhibited early establishment and growth of both clover and grasses at all biochar treatment levels. Entac plus biochar treatments significantly enhanced survivorship of willows following a drought treatment in a greenhouse trial. In a field trial, Entac treatments had positive effects on willow diameter growth. Collectively, these results suggest that better soil moisture retention is the principal mechanism responsible for enhanced survivorship and growth of planted willows treated with Entac and biochar on sand substrates. Given Entac's inhibitive effects on early establishment of herbaceous species, and the abilities of Entac and biochar in combination to mitigate drought stress, these treatments may be particularly well suited for ecological restoration efforts using planted tree stock on coarse‐textured substrates and where exposure and ingress of non‐native herbaceous species are of concern.     

Long‐term biochar application promotes rice productivity by regulating root dynamic development and reducing nitrogen leaching

Biochar is beneficial for improving soil quality and crop productivity. However, the long‐term effects of biochar addition on temporal dynamics of plant shoot and root growth, and the changes in soil properties and nitrogen (N) leaching are still obscure. Here, based on a long‐term (7 years) biochar field experiment with rice in northwest China, we investigated the effects of two biochar rates (0 and 9 t ha^?1 year^?1) and two N fertilizer rates (0 and 300 kg N ha^?1 year^?1) on shoot and root growth, root morphology, N leaching, and soil physicochemical properties. The results showed that both biochar and N fertilizer significantly promoted rice growth, with their interaction significant only in some cases. Both fertilizers enhanced rice shoot biomass and N accumulation in various growth stages as well as increased grain yield. Nitrogen fertilizer significantly promoted root growth regardless of biochar application. However, biochar application without N fertilizer increased root biomass and length during the whole growth period, except in the booting stage; biochar with N application promoted root growth at tillering, reduced root biomass but maintained root length with low root diameter and high specific root length during the jointing and booting stages, and then delayed root senescence in the grain filling stage. Long‐term applications of biochar and N fertilizer reduced 10%–12% bulk density of topsoil compared to the control treatment with no N fertilizer and no biochar. Long‐term biochar application also improved soil total organic carbon and concentrations of available N, phosphorus, and potassium. In addition, biochar and N fertilizer applied together significantly reduced nitrate and ammonium concentration in leachate at different soil depths. In conclusion, biochar could regulate root growth, root morphology, soil properties, and N leaching to increase rice N fertilizer‐use efficiency.     

生物炭对植烟土壤微生态和烤烟生理的影响

生物炭是农林废弃物资源化利用的研究热点之一.通过田间试验,研究了烟杆炭不同施用量(0、1、10、50 t·hm^-2)对植烟土壤微生态和烤烟生理特性的影响.结果表明: 烤烟各时期土壤含水量均随生物炭用量增加而增加;在烤烟旺长阶段,50 t·hm^-2处理的土壤含水量显著高于其他处理.随着生物炭用量的增加,土壤总孔隙度和毛管孔隙度逐渐增加,细菌、放线菌、真菌的数量表现为先增后减的趋势,其中生物炭用量10 t·hm^-2处理下数值最大.土壤早期呼吸速率随生物炭用量的增加而增大,与对照相比,生物炭处理土壤呼吸速率增幅为7.9%～36.9%,生物炭高用量(50和10 t·hm^-2)与对照差异显著.生物炭提升了烤烟叶片水势,增加了叶片类胡萝卜素和叶绿素含量,显著增加了根系、地上部和总干质量.说明生物炭在改良植烟土壤微生态和调控烤烟生理特性等方面具有积极效应.     

Simulated chronic NO3− deposition reduces soil respiration in northern hardwood forests

Chronic N additions to forest ecosystems can enhance soil N availability, potentially leading to reduced C allocation to root systems. This in turn could decrease soil CO₂ efflux. We measured soil respiration during the first, fifth, sixth and eighth years of simulated atmospheric NO₃^? deposition (3 g N m^?2 yr^?1) to four sugar maple‐dominated northern hardwood forests in Michigan to assess these possibilities. During the first year, soil respiration rates were slightly, but not significantly, higher in the NO₃^?‐amended plots. In all subsequent measurement years, soil respiration rates from NO₃^?‐amended soils were significantly depressed. Soil temperature and soil matric potential were measured concurrently with soil respiration and used to develop regression relationships for predicting soil respiration rates. Estimates of growing season and annual soil CO₂ efflux made using these relationships indicate that these C fluxes were depressed by 15% in the eighth year of chronic NO₃^? additions. The decrease in soil respiration was not due to reduced C allocation to roots, as root respiration rates, root biomass, and root turnover were not significantly affected by N additions. Aboveground litter also was unchanged by the 8 years of treatment. Of the remaining potential causes for the decline in soil CO₂ efflux, reduced microbial respiration appears to be the most likely possibility. Documented reductions in microbial biomass and the activities of extracellular enzymes used for litter degradation on the NO₃^?‐amended plots are consistent with this explanation.     

生物炭添加对不同水氮条件下芦苇生长和氮素吸收的影响

生物炭能改良土壤从而促进植物生长和氮素吸收，但其作用效果是否受水氮条件的影响尚不清楚。以湿地植物芦苇为研究对象，在3种氮添加水平（无添加，30 kg hm^-2 a^-1和60 kg hm^-2 a^-1）和两种水分（淹水和非淹水）条件下分别进行生物炭添加和不添加处理，结果表明：（1）生物炭添加能促进芦苇根系生长，在非淹水条件下根系生物量增加了40.5%，在淹水条件下根系生物量增加了20.1%。（2）生物炭添加能促进非淹水条件下芦苇的氮素吸收，能提高淹水条件下芦苇的氮素生产力。（3）生物炭添加加剧了土壤氮素损失，且在非淹水高氮条件下作用最强，可能是由于生物炭促进了芦苇的氮素吸收。芦苇氮素吸收速率与土壤氮损失之间存在显著的正相关关系。因此，在添加生物炭时，需要考虑土壤水分状况和氮素富集程度以及植物的氮素吸收偏好。该研究结果可为生物炭在湿地生态系统中的应用提供参考。