Sugarcane waste straw biochar and its effects on calcareous soil and agronomic traits of okra

Biochar has been considered a safe soil additive to enhance soil fertility and agronomic traits of different crops. This study was conducted to explore the impacts of sugarcane waste straw biochar on soil characteristics and some agronomic traits of okra. The experiment was carried out with four treatments, i.e., control, sugarcane waste straw biochar (10 ton ha^?1), farmyard manure (FYM, 10 ton ha^?1), and chemical fertilizers (NPK; 120:100:80 kg ha^?1) having three replications of each treatment. Soil samples were tested for texture, bulk density, particle density, pH, electrical conductivity (EC), organic matter content, nitrate nitrogen (NO₃-N), and extractable-P. The sugarcane waste straw biochar was characterized for plant major nutrient elements. The impact of various treatments was observed on soils and agronomic traits of okra like plant height, fruit size, fruit length, and yield of okra. Results revealed that sugarcane waste straw biochar expressed higher EC value and noticeable amounts of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and magnesium (Mg). The sugarcane waste straw biochar, in comparison with FYM and NPK, significantly improved the NO₃-N, extractable-P, OM and EC of the calcareous soil, and reduced the soil bulk density. Furthermore, plant growth and yield parameters were significantly improved under biochar application over the control, FYM and NPK. Overall, sugarcane waste straw biochar proved to be a good alternative to conventional organic and inorganic fertilizers under calcareous soil conditions.     

A field study investigating the potential use of phosphorus combined with organic amendments on cadmium accumulation by wheat and subsequent rice

A field study was performed to determine the efficiency of diammonium phosphate (DAP) applied alone or combined with biochar, lignite, and farmyard manure (FYM) on growth and cadmium (Cd) accumulation in wheat and rice. Before crop sowing, different treatments were applied in the field such as a control (T₁), DAP alone (0.1%, T₂), DAP + lignite (0.05% each, T₃), DAP + FYM (0.05% each, T₄), and DAP + biochar (0.05% each, T₅). Afterwards, the wheat seeds were sown in the soil. At wheat postharvest, rice was sown without any further treatment. Raw effluent was applied as an irrigation source during the whole growth period of both crops since it is the common practice of the farmers of study area. It was revealed that the use of amendments enhanced the yield and photosynthesis but lowered the Cd contents in straw as well as grains of both crops. In both crops, the highest yield of straw and grain was found in DAP + FYM whereas the lowest Cd concentration was found in DAP alone. The ammonium bicarbonate-DTPA extractable Cd of post wheat and post rice soils were decreased while the soil pH and immobilization index were increased in all treatments as compared with the control. The present field study highlighted that the DAP + FYM can be effective in increasing yield with decreased Cd concentrations in crop grains.     

蔗渣生物质炭对喀斯特农田石灰性土壤氮转化过程的短期影响

生物质炭对于土壤中不同形态氮库的含量影响已有较多研究,但对西南喀斯特区石灰性土壤氮素形态,尤其是控制氮素形态的转化过程研究较为缺乏。本研究设置土壤中添加1%(C1)和3%(C2)蔗渣生物质炭2个用量水平,并以不施用蔗渣生物质炭作为对照(CK),共3个处理,通过 15 NH 4 NO 3 和NH^15 4 NO 3 成对标记技术,结合MCMC氮素转化模型研究了不同用量的蔗渣生物质炭对石灰性土壤氮转化过程的短期影响,为该地区蔗渣资源化利用和土壤氮保持提供理论支撑。结果表明,与CK相比,添加蔗渣生物质炭能够快速提高土壤pH和有机碳含量。添加生物质炭并没有显著改变土壤氮的矿化、铵态氮(NH^+ 4 )和硝态氮(NO^- 3 )的微生物同化和异养硝化速率,但NH^+ 4 吸附速率随生物质炭用量的增加而提高,以添加量最高的C2处理最大。添加生物质炭同样提高了土壤NH^+ 4 释放速率,但C1和C2处理的土壤NH^+ 4 释放速率并无显著性差异。与CK和C1处理相比,施用高量蔗渣生物质炭通过抑制自养硝化速率而显著降低了硝态氮净产生速率。这些结果表明,施用高量蔗渣生物质炭于石灰性土壤中可快速实现对NH^+ 4 吸附,降低自养硝化速率,减少NO^- 3 产生,从而降低了其损耗和淋失风险。     

Phosphorus desorption kinetics in two calcareous soils amended with P fertilizer and organic matter

We studied the effects of poultry manure and pistachio compost with and without phosphorus fertilizer on the kinetics of phosphorus desorption in two calcareous soils of Kerman and Koohbanan farms in the southeastern of Iran. For this purpose mono potassium phosphate, at rates of 0, and 100 parts per million of phosphorus, and air-dried manure, at rates of 0 and 4% were mixed with the soils. The soils were incubated at 24–25°C and near field capacity for 90 days in the greenhouse. Afterwards, the desorption of P was studied by the successive extraction with 0.5 M NaHCO₃. The results of this research indicated that application of OM and fertilizer P combined increased P recovery in each of the extraction time, adding poultry manure and 100 mg phosphorus together to the soils, increased P desorption more than pistachio compost in the soils. The phosphorus desorption rate was initially rapid and then became slower until equilibrium was approached. Kinetic data were best described by power function and simple Elovich equations. Subsequent to these equations, parabolic diffusion equation was also well fitted the time-dependent P desorption data.     

Competitive adsorption of trace elements in calcareous soils as affected by sewage sludge,poultry manure,and municipal waste compost

The competitive adsorption of trace elements is a key issue in assessing the mobility of trace elements in calcareous soils and can be affected by disposal of sewage sludge, municipal waste, and poultry manure. The effect of municipal sewage sludge, poultry manure, and municipal waste compost on the sorption of cadmium (Cd), copper (Cu), zinc (Zn), and nickel (Ni) in surface samples of three calcareous soils was studied. As the applied concentrations increased, Cu and Cd adsorption increased, while Zn and Ni adsorption decreased in all treatments. Based on the distribution coefficient (K _d) values and proportion of increase or decrease in metal adsorption, the selectivity sequence in control and amended soils found was Cu ≫ Cd ≫ Ni > Zn and Cu ≫ Cd ≫ Zn > Ni, respectively. In general, among control and amended soils, control soils showed the highest K _d for Cd, Cu, and Ni, while sludge, poultry manure, and composted waste-amended soils had lowest K _d for Cd, Cu, and Ni, respectively. In the case of Zn, composted waste-amended and control soils had highest and lowest K _d, respectively. The present experimental results indicated that the addition of organic amendments to these calcareous soils reduced the sorption of Cd, Cu, and Ni. Thus, the effects of preferential adsorption and organic matter should be considered in assessing the risk associated with applying sewage sludge, poultry manure, and composted material to calcareous soils.     

Amelioration of soil acidity,Olsen-P,and phosphatase activity by manure- and peat-derived biochars in different acidic soils

To increase soil productivity, ameliorate nutrient scarcity, and reduce metal toxicity in highly weathered acidic soils usually requires fertilizer and lime application. Effects of three biochars on soil acidity, Olsen-phosphorus (P), phosphatase activities, and heavy metal availability were investigated to test potential of these biochars as soil amendments in highly weathered acidic soils. Incubation experiments were conducted for 6 weeks with three acidic soils: Alfisol, Ultisol, and Oxisol. Three biochars were derived from chicken manure (CMB), pig manure (PMB), and peat moss (PB) at 400 °C and applied at 1 or 2% (wt/wt). The addition of the three biochars increased Olsen-P in the three acidic soils in the following order: CMB?>?PMB?>?PB. Application of 2% CMB increased Olsen-P contents by 2.41-, 7.4-, and 1.78-fold in the Ultisol, Oxisol, and Alfisol compared with controls, respectively. Moreover, CMB increased the soil pH, electrical conductivity (EC), cation exchange capacity (CEC), and alkaline phosphatase activity, but reduced exchangeable acidity, acid phosphatase activity, and the availability of heavy metals—more effectively than PMB and PB. Addition of CMB increased soil pH by 0.90, 0.90, and 0.92 units for the Alfisol, Ultisol, and Oxisol, respectively, correspondingly followed by 0.80, 0.84, and 0.87 units for PMB and 0.15, 0.28, and 0.25 for PM. Changes in EC, CEC, and exchangeable acidity followed the same order for the three soils: CMB?>?PMB?>?PB. The results suggested that the magnitude of changes in soil properties and Olsen-P contents depended on biochar type and application rate. Application of CMB increased nutrient availability and reduced the availability of heavy metals more than other amendments. Due to higher pH, EC, and CEC, and greater concentrations of carbon, nitrogen, and exchangeable calcium and potassium, incorporation of CMB should be a better cost-effective method to correct soil acidity and improve fertility and Olsen-P contents in Ultisols and Oxisols from tropical and subtropical regions of the world.     

Comparison of the effects of conventional organic amendments and biochar on the chemical, physical and microbial properties of coal fly ash as a plant growth medium

The bulk of fly ash (an inorganic waste of coal-fired power generation) produced is deposited in disposal areas where it needs to be revegetated. The effects of addition of three conventional organic amendments (biosolids, poultry manure, green waste compost), or poultry manure-derived biochar, to coal fly ash (at two rates) on some key chemical, physical and microbial properties and on growth of Rhodes grass (Chloris gayana) was studied in a laboratory incubation/greenhouse study. Addition of all amendments, including biochar, increased concentrations of extractable Mg, K, Na and P and CEC_{(pH 7.0)}. Additions of poultry manure, and particularly biosolids, also greatly increased levels of extractable NH₄ ⁺ and NO₃ ⁻-N. Addition of biosolids, green waste compost and biochar resulted in a decrease in macroporosity, a concomitant increase in mesoporosity and, at the high rate of addition, an increase in available water-holding capacity. Basal respiration was very low in fly ash and was increased by addition of all amendments; metabolic quotient was markedly greater in control than amended treatments. Biosolids, poultry manure and green waste compost additions all increased microbial biomass C. Growth of Rhodes grass was extremely low under unfertilized conditions in control, biochar and, to a lesser extent, green waste compost treatments but addition of poultry manure and the lower rate of biosolids resulted in large increases in yields. Although biochar additions increased extractable Ca, K, P, Cu, Zn and Mn, CEC, mesoporosity and water-holding capacity, they had a little or no stimulatory effect on the size of the soil microbial community, N fertility or plant growth. This was attributable to the lack of metabolisable C and an insignificant N-supplying capacity.     

Residual impact of biochar on cadmium uptake by rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) grown in Cd-contaminated soil

Cadmium (Cd) is the family member of toxic heavy metals, and its accumulation in food crops has become a global environmental constraint. Biochar potentially minimizes the metal contents in plants, but limited work has been reported on its residual effect on subsequent crops. The residual effect of various biochar levels (0, 1.5, 3.0, and 5.0% w/w) on Cd accumulation in rice has been investigated in this study. Biochar treatments enhanced the rice growth, photosynthesis, and antioxidant enzymes, whereas diminished the Cd contents and oxidative stress in rice. Cadmium concentration in shoots decreased by 24.4, 36.6, and 57.5% in 1.5, 3.0, and 5.0% biochar treatments over the control. Biochar supply enhanced the soil pH and electrical conductivity, whereas diminished the soil bioavailable Cd. Overall, the results depicted a significant residual impact of rice straw biochar on rice growth attributes and Cd uptake. However, studies are still needed to explore the long-term sustainability of biochars prepared from different feedstocks on bioavailability of toxic metals in soils and uptake by food crops under field conditions.     

Phosphorus dynamics and corn growth under applications of corn stalks biochar in a clay soil

Biochar prepared from corn stalks is used as a source of phosphorus in this study. The hypotheses were to investigate effects of biochar applications in clay soil on availability, changes of phosphorus pools and maximum adsorption of phosphorus as well as corn growth. The soil was placed in plastic pots with each contains 3 kg of this soil. Biochar was added at levels of 0 (control), 6.5 (B₁), 19 (B₂), and 38 (B₃) g pot^?1. In this experiment, the pot was planted with corn (Zea mays). The results of this study revealed that the biochar application enhanced available phosphorus (Olsen-P) from 11.51 to 17.10 mg kg^?1. Adding biochar significantly increased the amount of NH₄Cl-P, NaHCO₃-P_o, and NaOH I-P_o fractions (p?≤?0.05), but it significantly decreased HCl-P_i fraction (p?≤?0.05). Addition of biochar at the highest level increased the fresh and dry matter productions by up to about 75 and 48.7%, respectively, compared to the control. The phosphorus uptake by corn plants significantly increased with increasing levels of biochar. The removal efficiency (% sorption) and maximum adsorption (b) of phosphorus increased with increasing level of biochar addition compared to control. Consequently, it is recommended to add biochar produced from corn stalks to the soil in order to substitute phosphate fertilizers.     

Drinking water treatment residuals as an amendment to alkaline soils: Effects on the growth of corn and phosphorus extractability

Drinking water treatment residuals (alum) are waste products of water purification that have potential for environmental remediation as a soil amendment and a potential plant growth medium. In this study, the influence of added Drinking water treatment residuals on the extractability and availability of phosphorus to plants; determination of the agronomic rate of alum to different agricultural soils and evaluation of the alum as ameliorating material for soil conditions and plant growth were investigated. In all studied soils, increasing drinking water treatment residuals rate up to 30 g/kg significantly increased dry matter yield. Application of 10, 20 and 30 g/kg alum significantly increased plant P concentrations in the plant materials (shoots and roots) taken from clay, sandy and calcareous soils. Further increase in alum application rate has resulted in negative significant impact on plants P concentration, especially in clay and calcareous soils, but in sandy soils the increase in phosphorusconcentration extended to 40 g/kg alum rate. Application of alum at rates up to 30 g/kg significantly increased available phosphorus concentrations of the three studied soils. However, application of alum at a rate of 40 g/kg to clay and calcareous soils significantly decreased available phosphorus concentrations. Combined analyses of all soils and alum rates studied clearly indicated significant relationship between available phosphorus concentration and phosphorus uptake (r = 0.87, P < 0.001). Based on our experiment results, the rate of 30 g/kg is considered the best application rate of alum because of its positive effects on plant dry matter. Our study clearly demonstrates that alum has potential as a soil amendment to increase plant growth; however, more research is needed to determine beneficial and / or detrimental aspects of this practice under field conditions.     

土壤中添加生物炭对Cr(Ⅵ)的迁移锁定作用研究

生物炭应用在土壤中具有CO₂减排、改善土壤性质等作用,研究表明生物炭土壤有助于农作物产量和质量的提高,同时对污染物有较好的吸附效果,能控制其迁移,但对于近年关注的土壤中Cr(Ⅵ)和生物炭的作用研究却很少。通过土柱淋滤实验,研究土壤中添加生物炭后对Cr(Ⅵ)的迁移影响,特别是对其进行模拟酸雨淋滤实验,进一步研究了生物炭土壤对Cr(Ⅵ)的锁定效果。结果表明：仅施加1%的生物炭,就能够大幅度提高土壤系统固定Cr(Ⅵ)的能力,小粒径生物炭对Cr(Ⅵ)的吸附固定能力更加明显,在一定条件下是大粒径的固定吸附量的3倍,在酸雨淋滤作用下也不易解吸,说明生物炭的添加能有效抑制Cr(Ⅵ)在土壤中的迁移,起到原位锁定的作用,这对农田土壤开发治理提供了重要手段和依据。     

长期定量施肥对土壤有机碳储量和土壤呼吸影响

利用1989年在河南省封丘县潮土上建立的用于研究有机肥（用小麦秸秆和饼肥沤制）和化学肥料对土壤有机碳和土壤生产力影响的长期定位试验，于2002年6月至2003年6月在玉米—小麦轮作期内对土壤呼吸进行了研究。试验包括化肥氮磷钾（NKP）、氮磷（NP）、氮钾（NK）、磷钾（PK）、有机肥（OM）、一半化学氮肥和一半有机氮（1/2OM）以及不施肥（CK）7个处理。试验结果表明：以有机肥或以化肥形式配合施用NPK不但可以极大提高土壤生产力，而且有益于增加土壤有机碳储量。有机肥对土壤有机碳含量的提高作用显著高于化肥。玉米生长期的土壤呼吸占全年呼吸量的56%～59%，小麦生长期只占32%～37%。土壤有机碳储量和土壤呼吸量与有机物质的投入有关。综合考虑经济效益（籽粒产量）和环境效益（全球变化），最佳的肥料配比是有机肥料和无机肥料配合施用，寻求合理可行的有机肥和化肥配合比率是实现农业土壤生产功能和环境功能协调统一的关键。     

Impact of biochar,bentonite, and compost on physical and chemical characteristics of a sandy soil

In this study, bentonite (Ben), compost (Com), and biochar (Bio) were used as soil amendments to enhance sandy soil physical properties. A soil column experiment was conducted in a laboratory. Application rates were 3% (weight/weight) of Bio (T₁), Ben (T₂), and Com (T₃). Furthermore, mixtures 1.5% and 1.5% of Bio and Ben (T₄), Ben and Com (T₅), and Bio and Com (T₆), and a mixture 1%, 1%, and 1% of Bio, Ben, and Com (T₇) in addition to control treatment were adopted. The mixtures of amendments and sandy soil were concentrated at the top 10 cm of columns. Results revealed that the cumulative evaporation was reduced by 2.3% and 5.7% as a result of using T₃ and T₅, respectively. However, the remaining treatments enhanced the cumulative evaporation. The application of amendments increased the capacity of the soil to maintain water by 35.4%, 24.4%, 13.3%, and 10.2%, for soils treated with T₅, T₃, T₇, and T₄, respectively. The water content at field capacity had the highest increase in the top 10 cm when treatment T₃ was used. Although T₃ (compost) was the most efficient for enhancing soil physical properties, this study recommends T₅ and T₇ to improve hydraulic properties of sandy soils. This is due to the fact that biochar and bentonite remain in the soil for a longer period and resist biodegradation while compost overcomes the negative impact of soil chemical properties as a result of biochar and bentonite additions.     

Biochar application in a tropical,agricultural region: A plot scale study in Tamil Nadu,India

A plot-scale evaluation of biochar application to agricultural soils was conducted in Tirunelveli, Tamil Nadu, India, to investigate the potential of biochar to improve soil fertility and moisture content. Biochar feedstocks need to be sustainably sourced: several locally available feedstocks (rice husk, cassia stems, palm leaves and sawdust) were analysed as proposed soil amendments so that no single biomass material is depleted to maintain biochar addition. The biochars from different biomass feedstock contained >20% C and were high in macro- and micronutrients. The results suggest that an application rate of 6.6 metric tonnes ha^?1 cassia biochar was enough to initiate C-accumulation, which is reflected in an increase in OM and a net reduction in soil bulk density.     

Understanding compost effects on water availability in a degraded sandy soil of Patagonia

Disturbances have the potential to reduce soil water and nutrient retention capacity by decreasing soil organic matter (SOM), which is particularly true for sandy soils characterized by an inherent low capacity to retain nutrients and water. To restore degraded areas, several works have shown positive effects of organic matter inputs on soil properties and plant growth. Despite these promising results, it is still unclear how organic matter inputs and plant growth modify the balance between soil nutrient and water supply. The objectives of the present work were (1) to evaluate the effects of biosolids compost and municipal compost addition on plant available water (PAW), soil moisture and soil temperature in a burned sandy soil of NW Patagonia (Argentina), and (2) to relate PAW and soil moisture with bulk density, soil organic carbon, nutrient availability (inorganic and potential mineralized nitrogen (N), extractable phosphorous) and aboveground phytomass. An experiment with excised vegetation and watering was also conducted. Compost application increased SOM, but it was insufficient to increase PAW. The increase in potential mineralized N in the amended soils indicated that during moist periods (and adequate temperatures), N uptake was increased, enhancing plant growth. As a consequence, higher plant water consumption in amended treatments resulted in lower soil moisture than in non-amended plots during the vegetative growth period that coincides with decreasing precipitation. Results indicate that a relatively high dose of compost (40 Mg ha^?1) applied to a sandy soil, contributed to increase nutrient availability and consequently, aboveground phytomass and water consumption.     

Effect of sheep manure and EDTA on the leaching of potassium from heavy metals contaminated calcareous soils

In this study, we examined the movement of potassium (K) in columns of contaminated calcareous soils by sheep manure and ethylene diamine tetraacetic acid (EDTA). Glass tubes, 4.9 cm in diameter and 40 cm in length, were packed with contaminated soils. The resulting 20-cm long column of soil had a bulk density of 1.3–1.4 g cm⁻³. Columns were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl₂, and sheep manure extract solutions. The amounts of K leached varied considerably between different soils (sandy loam and loamy sand) and leaching solutions. The amount leached with EDTA solution, varied from 7.2 to 66.7% of the extractable K when 20 pore volumes had passed through the column. The breakthrough curves of K in the EDTA and CaCl₂ were approximately similar, indicating they have similar ability to displace K from these contaminated calcareous soils. Thus, among leaching solutions application of EDTA and CaCl₂ on contaminated soils might enhance the mobility of K and large amounts of K will be leached.     

天然胶结钙质土强度及微观结构研究

自20世纪80年代起,国内就开展了关于岛礁钙质土岩土工程性质的研究工作,至今已经取得了大量的研究成果,但上述研究工作均是针对松散钙质土进行的,针对岛礁上广泛分布的胶结钙质土的研究工作尚未系统开展。而国外大量工程实践表明,胶结钙质土具有完全不同于松散钙质土的工程性状。针对天然胶结钙质土的空间各向异性,从微观角度研究影响其强度的主要参数,为今后的胶结钙质土的分类研究提供理论指导。文中采用多种试验研究方法,最后建立了天然胶结钙质土的密度、胶结度、孔隙度、颗粒大小等参数与强度间的对应关系,当前的研究结果表明,天然胶结钙质土的密度及胶结度与强度间存在良好的相关性。     

全吸力范围生物炭−黏土混合土的土−水特性

土−水特征曲线在研究非饱和土的水力与力学特性中发挥着重要的作用。生物炭具有多孔结构、高比表面积和强吸附的特性。将生物炭改性土应用于垃圾填埋场上覆盖层,因受自然环境因素的影响会使其水力特性发生改变。为了研究全吸力范围内生物炭掺量对生物炭−黏土混合土保水特性的影响,利用蒸汽平衡法（吸力范围 3～368 MPa）、滤纸法（吸力范围 0 ～40 MPa）和压力板法（吸力范围 0～1.5 MPa）控制土样的吸力,测定吸力平衡后土样的含水率和饱和度,得到全吸力范围内生物炭−黏土混合土的土−水特征曲线。试验结果表明：（1）3种吸力测试方法很好地表达了生物炭−黏土混合土全吸力范围内的土−水特征曲线。（2）生物炭能够影响黏土的保水性,但在一定的吸力范围内,生物炭−黏土混合土的保水性还与孔隙结构和孔隙中水的形态相关。（3）通过压力板法测得,试样的进气值随着生物炭掺量的增加而减小。当吸力值小于进气值时,曲线出现水平段,土样始终处于饱和状态,生物炭掺量越大,试样的保水性越好。（4）由生物炭−黏土混合土微观孔隙结构以及生物炭在黏土中的分布形态来解释生物炭改性黏土的保水能力随生物炭掺量的变化关系。     

Chemical and bioassay characterisation of nitrogen availability in biochar produced from dairy manure and biosolids

Biochar is charcoal made from waste biomass and intended to be added to soil to improve soil function and reduce emissions from the biomass caused by natural degradation to CO₂. Nitrogen (N) forms in biochar can be complex and their lability likely to be influenced by pyrolysis temperature which, together with the nature of carbon (C), will influence N mineralisation or immobilisation. These complex relationships are poorly understood, yet impact strongly on the potential agronomic value of biochar. In this study, N in different biochar samples produced from human and animal waste streams (biosolids and cow manure; each mixed with eucalyptus wood chips in a 1:1 dry wt. ratio) at different pyrolysis conditions (highest heating temperature 250, 350, 450 and 550 °C) was extracted with 6 M HCl. The acid hydrolysable, extractable N (THN) was fractionated into ammonia N (AN), amino acid N (AAN), amino sugar N (ASN) and uncharacterisable hydrolysable N (UHN). Biochar samples were also treated with 0.167 M K₂Cr₂O₇ acid to determine N potentially available in the long term. An incubation study of the different biochar samples mixed with acid washed sand was conducted at 32 °C for 81 days to study both C and N turnover. During incubation, the CO₂ released was trapped in NaOH and quantified. Hydrolysable N decreased as pyrolysis temperature increased from 250 to 550 °C. Fractionation into AN, AAN, ASN and UHN revealed progressive structural rearrangement of N with pyrolysis temperature. Based on HCl hydrolysis and dichromate oxidation results, C and N in biochar became more stable as pyrolysis temperature increased. The ratio of volatile C to THN was a useful indicator of whether net N mineralisation or immobilisation of N in biochar occurred. THN thus seems a sound estimate of the labile N fraction in biochar in the short term; however, dichromate-oxidisable N is probably more meaningful in the long run. Further studies using different types of biochar need to be conducted under more realistic conditions to obtain more information on N availability in biochar once in soil.