Effects of biochars derived from different feedstocks and pyrolysis temperatures on soil physical and hydraulic properties

Purpose

Biochar addition to soils potentially affects various soil properties, and these effects are dependent on biochars derived from different feedstock materials and pyrolysis processes. The objective of this study was to investigate the effects of amendment of different biochars on soil physical and hydraulic properties.

Materials and methods

Biochars were produced with dairy manure and woodchip at temperatures of 300, 500, and 700 °C, respectively. Each biochar was mixed at 5 % (w/w) with a forest soil, and the mixture was incubated for 180 days, during which soil physical and hydraulic properties were measured.

Results and discussion

Results showed that the biochar addition significantly enhanced the formation of soil macroaggregates at the early incubation time. The biochar application significantly reduced soil bulk density, increased the amount of soil organic matter, and stimulated microbial activity at the early incubation stage. Saturated hydraulic conductivities of the soil with biochars, especially produced at high pyrolysis temperature, were higher than those without biochars on the sampling days. The treatments with woodchip biochars resulted in higher saturated hydraulic conductivities than the dairy manure biochar treatments. Biochar applications improved water retention capacity, with stronger effects by biochars produced at higher pyrolysis temperatures. At the same suction, the soil with woodchip biochars possessed higher water content than that with the dairy manure biochars.

Conclusions

Biochar addition significantly affected the soil physical and hydraulic properties. The effects were different with biochars derived from different feedstock materials and pyrolysis temperatures.     

The dynamic changes of phosphorus availability in straw/biochar-amended soils during the rice growth revealed by a combination of chemical extraction and DGT technique

Purpose

This study compares the dynamic effects of straw and biochar on soil acidity and phosphorus (P) availability in the rice growth period to reveal how straw and biochar affect the availability of phosphorus in soil and utilization of P for rice crop.

Materials and methods

In the pot experiment, rice straw, canola stalk, and corresponding biochars were mixed uniformly with the Ultisol. Soil samples were collected at four stages of rice growth to analyze the dynamic changes of soil acidity and P availability. The availability of phosphate in straw/biochar-amended soils were evaluated using a combination of chemical extraction and diffusive gradients in thin films (DGT) technique.

Results

Soil pH, KCl-P, Olsen-P, DGT-P, and Al-P deceased with the rice growth, while Fe-P increased. Biochar increased soil pH and P availability more than straw returning, especially in the mature stage, while the DGT-P only increased in the tillering stage. The DGT-induced fluxes in sediments (DIFS) model revealed that all treatments increased the capacity of soil solid phase supplementing P to pore water in the filling and mature stages. The content of total P in different rice tissues followed the order of grain?>?straw?>?root, and RB350 treatment had the highest P content in rice tissues. In the mature stage, soil pH had positive correlations with KCl-P and Olsen-P, and soil Fe-P had positive correlations with total P of root and straw.

Conclusions

Application of biochar made at 550 ℃ resulted in a larger increase in available P in soil, while biochar made at 350 ℃ had more effect on the chemical forms of P. The canola stalk biochar showed a larger influence on the P availability than rice straw biochar. Biochar treatments had a larger effect on inhibiting soil acidification and improving P availability than straw returning directly.

     

Short-term effects of raw rice straw and its derived biochar on greenhouse gas emission in five typical soils in China

Abstract

A short-term study was conducted to investigate the greenhouse gas emissions in five typical soils under two crop residue management practices: raw rice straw (Oryza sativa L., cv) and its derived biochar application. Rice straw and its derived biochar (two biochars, produced at 350 and 500°C and referred to as BC350 and BC500, respectively) were incubated with the soils at a 5% (weight/weight) rate and under 70% water holding capacity for 28 d. Incorporation of BC500 into soils reduced carbon dioxide (CO₂) and nitrous oxide (N₂O) emission in all five soils by 4?40% and 62?98%, respectively, compared to the untreated soils, whereas methane (CH₄) emission was elevated by up to about 2 times. Contrary to the biochars, direct return of the straw to soil reduced CH₄ emission by 22?69%, whereas CO₂ increased by 4 to 34 times. For N₂O emission, return of rice straw to soil reduced it by over 80% in two soils, while it increased by up to 14 times in other three soils. When all three greenhouse gases were normalized on the CO₂ basis, the global warming potential in all treatments followed the order of straw > BC350 > control > BC500 in all five soils. The results indicated that turning rice straw into biochar followed by its incorporation into soil was an effective measure for reducing soil greenhouse gas emission, and the effectiveness increased with increasing biochar production temperature, whereas direct return of straw to soil enhanced soil greenhouse gas emissions.     

Rice straw biochar amended soil improves wheat productivity and accumulated phosphorus in grain

Abstract

Biochar is a pyrolyzed biomass produced under limited oxygen or oxygen absent conditions. Few investigations have been conducted to determine the combined effect of biochar with chemical fertilizer on growth, yield and nutrient distribution pattern in root, shoot and grain in wheat as well as changes in soil physiochemical properties. This research was designed to study the combined effect of chemical fertilizer and rice straw-derived biochar on soil physio-chemical properties, growth, yield and nutrient distribution pattern within wheat plant tissue and grain. Results showed that rice straw biochar caused a significant decrease in soil pH and increase in soil organic matter as well as nutrients like total nitrogen (TN), potassium (K), magnesium (Mg) and boron (B) due to incubation. Result also showed that root biomass and straw did not differ between Bangladesh Agricultural Research Council (BARC) and ½ BARC?+?rice straw biochar treatment. Similarly, thousand grain weight and grain yield did not differ between the same treatments. The phosphorus concentration in wheat grain was highest in ½ BARC?+?rice straw biochar as compared to other treatments. The use of rice straw biochar in addition to the chemical fertilizers in wheat production systems is an economically feasible and practical nutrient management practice. Our findings urged that reduction of chemical fertilizer application is possible with supplementation of rice straw biochar.     

Saturated permeability behavior of biochar-amended clay

Purpose

Biochar has the characteristics of loose porosity, high specific surface area, and strong adsorption properties. Recently, the compacted biochar amended clay has been proposed as a sustainable alternative material for the final cover of landfills. However, the effect of biochar on saturated hydraulic conductivity (k_sat) is not yet conclusive. The objective of this study was to determine the influence of biochar content on the permeability of biochar-clay mixed soils.

Materials and methods

The clay used in the study belongs to the low liquid limit clay. The biochar is produced by heating the rice straw under an oxygen-deficient condition at a temperature of 500 °C. To study the effect of biochar content on the permeability of biochar-clay mixed soils, the biochar-clay mixed soils with the mass percentage of biochar being 0%, 5%, 10%, 15%, and 20% were used. The saturated hydraulic conductivity of the biochar-clay mixed soils was measured by the head pressure control permeameter. Meanwhile, the micro-pore structure of the saturated biochar-clay mixed soils was obtained by the nuclear magnetic resonance (NMR) technique.

Results and discussion

It can be observed that the saturated hydraulic conductivity k_sat of biochar-clay mixed soils increases linearly as the biochar content increases. The NMR results show that the T₂ distribution curve of pure clay is a unimodal pattern, while the T₂ distribution curve of biochar-clay mixed soils presents the bimodal pattern, where T₂ is the transverse relaxation time, reflecting the pore size of the soil specimens. With the increase of biochar content, the T₂ spectrum of the mixed soils moves slightly to the right, and T₂ at main peak increases gradually, correspondingly the most probable pore size of biochar-clay mixed soils increases.

Conclusions

The pore size distribution of the soil was changed by the addition of biochar and subsequently affects the permeability of biochar-clay mixed soils. This study provides some useful suggestions for optimizing the pore structure of the biochar amended clay anti-seepage layer in the final cover of landfills.

     

碳氮添加对雨养农田土壤物理性状的影响

为探明添加不同碳源及不同量氮肥4年后对土壤物理性质、产量的影响,依托布设于甘肃省定西市安定区李家堡镇的不同碳源田间定位试验,设置2种碳源(生物质炭15t/hm^2,秸秆4.5t/hm^2),3个氮肥施用量(0,50,100kg/hm^2),共计9个处理。研究了生物质炭、秸秆配施氮肥对试区土壤容重、总孔隙度、土壤饱和导水率、土壤团聚体稳定性、产量的影响。结果表明:较之无碳添加处理,添加生物质炭或秸秆均可改善土壤物理性质,但生物质炭效果最好。秸秆输入对0-5cm土层土壤容重的降低和总孔隙度、水稳性团聚体稳定性的提升具有显著效应,对土壤饱和导水率和0-30cm各土层机械稳定性团聚体稳定性的提升具有显著效应,而生物质炭对0-30cm各土层的土壤物理指标的改善均具有显著效应。氮素添加对土壤物理指标影响较小。生物质炭、秸秆、氮素均可促进作物增产,总体而言,生物质炭增产效果优于秸秆,尤其是生物质炭15t/hm^2+施纯氮100kg/hm^2处理。因此,添加生物质炭更有利于该区土壤物理性质的改善和产量的增加。     

Retention and release of diethyl phthalate in biochar-amended vegetable garden soils

Purpose

Diethyl phthalate (DEP) is one of the most commonly used plasticizers as well as a soil contaminant. Using biochar to remediate soils contaminated with DEP can potentially reduce the bioavailability of DEP and improve soil properties. Therefore, a laboratory study was conducted to evaluate the effect of biochar on soil adsorption and desorption of DEP.

Materials and methods

Two surface soils (0–20 cm) with contrasting organic carbon (OC) contents were collected from a vegetable garden. Biochars were derived from bamboo (BB) and rice straw (SB) that were pyrolyzed at 350 and 650 °C. Biochars were added to two types of soil at rates of 0.1 and 0.5 % (w/w). A batch equilibration method was used to measure DEP adsorption-desorption in biochar treated and untreated soils at 25 °C. The adsorption and desorption isotherms of DEP in the soils with or without biochar were evaluated using the Freundlich model.

Results and discussion

The biochar treatments significantly enhanced the soil adsorption of DEP. Compared to the untreated low organic matter soil, the soils treated with 0.5 % 650BB increased the adsorption by more than 19,000 times. For the straw biochar treated soils, the increase of DEP adsorption followed the order 350SB?>?650SB. However, for the bamboo biochars, the order was 650BB?>?350BB. Bamboo biochars were more effective than the straw biochars in improving soils’ adsorption capacity and reducing the desorption ability of DEP.

Conclusions

Adding biochar to soil can significantly enhance soil’s adsorption capacity on DEP. The 650BB amended soil showed the highest adsorption capacity for DEP. The native soil OC contents had significant effects on the soils’ sorption capacity treated with 650BB, whereas they had negligible effects on the other biochar treatments. The sorption capacity was affected by many factors such as the feedstock materials and pyrolysis temperature of biochars, the pH value of biochar, and the soil organic carbon levels.     

Effects of biochars produced from different feedstocks on soil properties and sunflower growth

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.     

铝改性秸秆生物质炭去除水体中的大肠杆菌

用一次平衡实验和柱淋溶实验研究了秸秆生物质炭和铝改性秸秆生物质炭对水中大肠杆菌的吸附量和去除率。结果表明,未改性秸秆生物质炭对大肠杆菌的吸附量很低,铝改性秸秆生物质炭对大肠杆菌有很高的吸附容量和去除率,0.6 mol/L Al(Ⅲ)改性生物质炭对大肠杆菌的去除效果优于0.3 mol/L Al(Ⅲ)改性生物质炭。当大肠杆菌浓度低于0.63 mg/ml时,铝改性大豆秸秆炭对大肠杆菌的去除率达100%,铝改性花生秸秆炭和铝改性稻草炭对大肠杆菌的去除率在96%和90%以上。0.5 mg/ml的大肠杆菌悬液通过装有2 g铝改性稻草炭的淋溶柱,每次收集10 ml淋出液,共收集152次,大部分淋出液中大肠杆菌浓度小于0.02 mg/ml,大肠杆菌去除率在95%以上。因此,铝改性生物质炭可用于水体中大肠杆菌的去除。     

Chemical fractions and bioavailability of nickel in a Ni-treated calcareous soil amended with plant residue biochars

ABSTRACT

Recently, the use of biochars for stabilization of soil heavy metals has been expanded due to their adsorption characteristics, low cost and carbon storage potential. A factorial experiment was performed to investigate the effects of two plant residue biochars (licorice root pulp and rice husk biochar each applied at 2.5% (w/w)) produced at two temperatures (350 and 550 °C), and three Ni application rates (0, 150 and 300 mg Ni kg^?1) on bioavailability and chemical fractions of Ni in a calcareous soil after spinach cultivation. Application of all the biochars significantly reduced Ni bioavailability factor (5–15%) and spinach Ni concentration (54–77%) in Ni-treated soil. The biochars produced at 550 °C were more effective at reducing Ni mobility and Ni uptake by spinach than those produced at 350 °C, attributed to higher CaCO₃ and lower acidic functional group content, which resulted in greater enhancement of soil pH. When comparing the biochars produced at the same temperature, the rice husk biochars were the most effective in reducing Ni bioavailability, likely due to their lower acidic functional group content and higher nano-silica content which resulted in higher soil pH values and potentially promoted the formation of Ni-silicates and hydroxides.

Abbreviations : Ni: Nickel; RHB: rice husk biochar; LRB: licorice root pulp biochar; WsEx: water soluble and exchangeable; CARB: carbonate form; RES: residual; MnOx; manganese oxides bound; AFeOx; amorphous iron oxides bound; CFeOx: crystalline iron oxides bound; OM: organic bound.     

生物炭对沙质土水分蒸发和导水率的影响

Biochar, as a kind of soil amendment, has important effects on soil water retention. In this research, 4 different kinds of biochars were used to investigate the influences of biochar addition on hydraulic properties and water evaporation in a sandy soil from Hebei Province, China. Biochar had strong absorption ability in the sandy soil. The ratio of water content in the biochar to that in the sandy soil was less than the corresponding ratio of porosity. Because of the different hydraulic properties between the sandy soil and the biochar, the saturated hydraulic conductivity of the sandy soil gradually decreased with the increasing biochar addition. The biochar with larger pore volume and average pore diameter had better water retention. More water was retained in the sandy soils when the biochar was added in a single layer, but not when the biochar was uniformly mixed with soil. Particle size of the added biochar had a significant influence on the hydraulic properties of the mixture of sand and biochar. Grinding the biochar into powder destroyed the pore structure, which simultaneously reduced the water absorption ability and hydraulic conductivity of the biochar. For this reason, adding biochar powder to the sandy soil would not decrease the water evaporation loss of the soil itself.     

Effects of straw and its biochar applications on the abundance and community structure of CO2-fixing bacteria in a sandy agricultural soil

Purpose

Crop straw and biochar application can potentially increase carbon sequestration and lead to changes in the microbial community in agricultural soils. Sequestration of CO₂ by autotrophic microorganisms is key to biogeochemical carbon cycling in soil ecosystems. The effects of straw and its biochar, derived from slow pyrolysis, on CO₂ fixation bacteria in sandy soils, remain unclear. Therefore, this study compared the response of abundance and community of CO₂ fixation bacteria to the two straw application methods in a sandy agricultural soil. The overall aim of the study was to achieve an efficient use of straw residues for the soil sustainablility.

Materials and methods

We investigated the soil organic carbon content and autotrophic bacteria over four consecutive years (2014–2018) in a field experiment, including the following four treatments: whole maize straw amendment (S), whole maize straw translated biochar amendment (B), half biochar and half straw amendment (BS), and control (CK) without straw or biochar amendment. The autotrophic bacterial abundance and community structure were measured using molecular methods of real-time PCR, terminal restriction fragment length polymorphisms (T-RFLP), and a clone library targeting the large subunit gene (cbbL) of ribulose-1,5-bisphosphate carboxylase/oxygenase.

Results and discussion

The results showed that the content of soil total organic carbon (TOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC) in B, S, and BS treatments was significantly increased compared with the CK treatment. Soil TOC and available potassium (AK) in the B treatment significantly increased by 15.4% and 23.3%, respectively, but soil bulk density, DOC, and MBC significantly decreased by 8.5%, 10.6%, and 14.5%, respectively, compared with the S treatment. The abundance of the cbbL gene as well as of the bacterial 16S rRNA gene increased significantly in straw or biochar application treatments as compared to the CK treatment. The B treatment, but not the BS treatment, significantly increased the cbbL gene abundance when compared to the S treatment. No significant differences were observed in the bacterial 16S rRNA gene abundance among the three straw or biochar applications. The application of straw biochar could increase the diversity of the autotrophic bacteria, which also altered the overall microbial composition. Physicochemical properties of the soil, such as soil pH, SOC, and bulk density, can help explain the shift in soil microbial composition observed in the study.

Conclusions

Taken together, our results suggest that straw biochar, rather than straw application, leads to an increase in the abundance and diversity of CO₂-fixing bacteria, which would be advantageous for soil autotrophic CO₂ fixation.

     

Influence of Biochar Addition on the Denitrification Process and N<Subscript>2</Subscript>O Emission in Cd-Contaminated Soil

The aim of this study was to investigate the effect of biochar addition on the denitrification process and N₂O emission in Cd-contaminated soil. Four different biochars, i.e., dairy manure and rice straw pyrolyzed at 350 and 550 °C, respectively, were added into a Cd-contaminated soil and incubation experiments were conducted for 8 weeks. Results showed that Cd had an inhibitory effect on denitrifying reductase enzymes and reduced the abundance of functional genes. On the contrary, amendment with the biochars increased denitrifying enzyme activity and gene abundance, and thus, enhanced the denitrification process. Labile carbon (C) in the biochar-amended soil, which was calculated based on the two-pool exponential model, was the key factor to facilitate this process. As a less important factor, elevated soil pH by biochar addition also increased denitrifying activity as well as the nosZ abundance. Decrease of Cd bioavailability by the biochar addition was beneficial to the denitrification process. Addition of the biochars with higher amount of NO₃ ^?-N, especially the rice straw-derived biochars, increased cumulative N₂O emission by more than ten times relative to the Cd-contaminated soil. With the great amount of labile C and NO₃ ^?-N, the treatment of biochars prepared at 350 °C released the larger amount of CO₂ and N₂O than other treatments. The biochar addition could totally release the heavy metal stress and restore the Cd-contaminated soil in terms of bacterial community.     

Influence of nitrogen fertilizer forms and crop straw biochars on soil exchange properties and maize growth on an acidic Ultisol

Effects of repeated application of urea (UN) and calcium nitrate (CN) singly and together with crop straw biochars on soil acidity and maize growth were investigated with greenhouse pot experiments for two consecutive seasons. Canola straw biochar (CB), peanut straw biochar (PB) and wheat straw biochar (WB) were applied at 1% of dried soil weight in the first season. N fertilizers were applied at 200 mg N kg^?1. In UN treatments, an initial rise in pH was subjected to proton consumption through urea hydrolysis, afterwards nitrification of NH₄⁺ caused drastic reductions in pH as single UN had soil pH of 3.70, even lower than control (4.27) after the 2nd crop season. Post-harvest soil analyses indicated that soil pH, soil exchangeable acidity, NH₄⁺, NO₃^? and total base cations showed highly significant variation under N and biochar types (P < 0.05). Articulated growth of plants under combined application with biochars was expressed by 22.7%, 22.5%, and 35.7% higher root and 25.6%, 23.8%, and 35.9% higher shoot biomass by CB, PB and WB combined with CN over UN, respectively. Therefore, CN combined with biochars is a better choice to correct soil acidity and improve maize growth than UN combined with biochars.     

生物炭对沙质土水分蒸发和导水率的影响（英文）

Biochar,as a kind of soil amendment,has important effects on soil water retention.In this research,4 different kinds of biochars were used to investigate their influences on hydraulic properties and water evaporation in a sandy soil from Hebei Province,China.Biochar had strong absorption ability in the sandy soil.The ratio of water content in the biochar to that in the sandy soil was less than the corresponding ratio of porosity.Because of the different hydraulic properties between the sandy soil and the biochar,the saturated hydraulic conductivity of the sandy soil gradually decreased with the increasing biochar addition.The biochar with larger pore volume and average pore diameter had better water retention.More water was retained in the sandy soil when the biochar was added in a single layer,but not when the biochar was uniformly mixed with soil.Particle size of the added biochar had a significant influence on the hydraulic properties of the mixture of sand and biochar.Grinding the biochar into powder destroyed the pore structure,which simultaneously reduced the water absorption ability and hydraulic conductivity of the biochar.For this reason,adding biochar powder to the sandy soil would not decrease the water evaporation loss of the soil itself.     

Responses of Soil Microbial Community Structure and Activity to Incorporation of Straws and Straw Biochars and Their Effects on Soil Respiration and Soil Organic Carbon Turnover

Like straw, biochar incorporation can influence soil microorganisms and enzyme activities and soil carbon(C) responses; however,few studies have compared the various effects of straw and biochar and the underlying mechanisms. An experiment was performed to study the changes in soil respiration(SR) and soil organic C(SOC) fluxes in response to the incorporation of three kinds of straw(reed, smooth cordgrass, and rice) and their pyrolyzed products(biochars) at Chongming Island, China. In addition, the microbial activity and community structure of some amended soils were also analyzed to clarify the mechanisms of these responses. The results showed that all biochar incorporation(BC) induced lower SR than the corresponding unpyrolyzed straw incorporation(ST), and the average SR in the soils following BC and ST during the experimental periods was 21.69 and 65.32 μmol CO_2 m~(-2)s~(-1), respectively.Furthermore, the average SOC content was 16.97 g kg~(-1) following BC, which was higher than that(13.71 g kg~(-1)) following ST,indicating that compared to ST, BC was a low-C strategy, even after accounting for the C loss during biochar production. Among the BC treatments, reed-BC induced the lowest SR(17.04 μmol CO_2 m~(-2)s~(-1)), whereas smooth cordgrass-BC induced the highest SR(27.02 μmol CO_2 m~(-2)s~(-1)). Furthermore, in contrast with ST, BC significantly increased the abundance of some bacteria with poorer mineralization or better humification ability, which led to lower SR. The lower easily oxidizable C(EOC) and higher total C contents of biochars induced lower SR and higher SOC in the soil following BC compared to that following ST. Among the BC treatments,the higher total nitrogen content of rice biochar led to significantly higher soil microbial biomass, and the lower EOC content of reed biochar led to lower soil microbial activity and SR.     

Biochar reduced soil extractable Cd but increased its accumulation in rice (Oryza sativa L.) cultivated on contaminated soils

Purpose

This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions.

Materials and methods

Pot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%.

Results and discussion

The application of 5% biochar reduced CaCl₂-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe²⁺ in soils and formation of Fe plaques on roots and weakened the Fe²⁺-Cd²⁺ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl^?. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot.

Conclusions

Rice straw biochar (with high concentration of water-soluble Cl^?) reduced CaCl₂-extractable soil Cd but increased Cd concentration in rice under flooding condition.

     

几种保水材料对砂质潮土水分参数的影响

针对砂质潮土水分容量低、持水性差、渗透性强的问题,通过土柱试验比较几种保水材料与沙土培养前后对水分运动参数的改善效果。试验保水材料为:2%生物炭、2%秸秆和0.1%保水剂,施入方式包括2种:与沙土混匀和25 cm处铺层。结果表明:2%生物炭和2%秸秆与沙土混匀总入渗时间分别为各自铺层处理的1.88倍和1.66倍,入渗完成时入渗率降低;而0.1%保水剂在土柱中铺层比混匀延长1.82倍。不同土柱总入渗时间依次为保水剂铺层 > 保水剂混匀 > 秸秆混匀 > 生物炭混匀 > 不添加保水材料的对照（CK）＝秸秆铺层 > 生物炭铺层。混匀处理土柱培养30 d后,各土柱总入渗完成时间均大于培养前,其中生物炭与秸秆总入渗时间分别提高了2.88倍与1.50倍,极大改善沙土漏水。与CK相比,生物炭、秸秆和保水剂的饱和导水率分别降低了6.1%,22.3%,82.4%;培养30 d后分别降低了77.2%,10.5%,79.1%。综上,保水剂铺层施用效果好于混匀,而其余材料与沙土混匀效果较好;随施用时间延长,生物炭和秸秆对沙土水分参数的改善效果较为明显,本结果可以为砂质潮土渗透、持水能力的改良提供方法及数据参考。     

Effects of conocarpus biochar on hydraulic properties of calcareous sandy soil: influence of particle size and application depth

A laboratory column experiment was conducted to investigate the effects of 400°C biochar at application rate of 15 g kg^?1 (21.9 t ha^?1) with different particle sizes (<0.5 mm (S₁), 0.5–1 mm (S₂) and 1–2 mm (S₃)) and application depths (0–2 cm depth (D₀), 4–6 cm depth (D₅) and 8–10 cm depth (D₁₀)) on hydro-physical properties of sandy loam soil. The results indicated that applying biochar decreased the waterfront and saturated hydraulic conductivity of sandy loam soil. The cumulative evaporation was the highest and amounted to 40.9 mm in the non-treated soil, but it recorded the lowest amount of 32.2–35.5 mm in the biochar-treated soil. Applying biochar caused significant increases in the amount of conserved and retained water with the highest amount of water conserved in soil treated with S₂ biochar at D₅. Moreover, the cumulative water infiltration through the soil was significantly reduced by S₁ and S₂ biochars at D₀. The values of saturated hydraulic conductivity for biochar treatments were significantly lower than those for the control, with the lowest values for S₁ at D₀ and D₅. These results suggest positive improvement for the hydro-properties of coarse-textured soils following biochar addition, especially with finer particles of biochar.