Increase in soil carbon sequestration using rice husk charcoal without stimulating CH4 and N2O emissions in an Andosol paddy field in Japan

Abstract

Biochar application has been recognized as an effective option for promoting carbon (C) sequestration, but it may also affect the production and consumption of methane (CH₄) and nitrous oxide (N₂O) in soil. A 1-year field experiment was conducted to investigate the effects of rice husk charcoal application on rice (Oryza sativa L.) productivity and the balance of greenhouse gas exchanges in an Andosol paddy field. The experiment compared the treatments of rice husk charcoal applied at 10, 20 and 40 Mg ha^?1 (RC10, RC20 and RC40, respectively), rice husk applied at 20 Mg ha^?1 (RH20), and the control (CONT). Rice straw and grain yields did not significantly differ among the treatments. The seasonal cumulative CH₄ emissions were 38–47% higher from RC10, RC20 and RC40 than from the CONT. However, the increases were not in proportion to the application rates of rice husk charcoal, and their values did not significantly differ from the CONT. On the contrary, the RH20 treatment significantly increased the cumulative CH₄ emission by 227% compared to the CONT. The N₂O emissions during the measurement were not affected by the treatments. As a result, the combined global warming potential (GWP) of CH₄ and N₂O emissions was significantly higher in RH20 than in the other treatments. There was a positive linear correlation between C storage in the top 10 cm of soil and the application rate of rice husk charcoal. The increases in soil C contents compared to the CONT corresponded to 98–149% of the C amounts added as rice husk charcoal and 41% of the C added as rice husk. Carbon dioxide (CO₂) fluxes in the off season were not significantly different among RC10, RC20, RC40 and CONT, indicating that C added as rice husk charcoal remained in the soil during the fallow period. The CO₂ equivalent balance between soil C sequestration and the combined GWP indicates that the rice husk charcoal treatments stored more C in soil than the CONT, whereas the RH20 emitted more C than the CONT. These results suggest that rice husk charcoal application will contribute to mitigating global warming without sacrificing rice yields.     

Changes in phosphorus fractions in three tropical soils amended with corn cob and rice husk biochars

ABSTRACT

The formation of phosphorus (P) compounds including iron-P, aluminum-P and calcium-P in highly weathered tropical soils can be altered upon biochar addition. We investigated the effect of corn cob biochar (CC) and rice husk biochar (RH) pyrolyzed at three temperatures (300°C, 450°C and 650°C) on phosphorus (P) fractions of three contrasting soils. A 90d incubation study was conducted by mixing biochar with soil at a rate of 1% w/w and at 70% field capacity. Sequential P fraction was performed on biochar, soil and soil-biochar mixtures. Increase in most labile P (resin-P_i, NaHCO₃-P_i) and organic P fraction (NaHCO₃-P_o + NaOH-P_o) in CC and RH biochars were inversely related to increasing temperature. HCl-P_i and residual P increased with increasing temperature. Interaction of CC and RH with soils resulted in an increase in most labile P as well as moderately labile P (NaOH-P_i) fractions in the soils. CC increased most labile P in the soils more than RH. The increase in most labile P fraction in soils was more significant at relatively lower temperatures (300°C and 450°C) than 650°C. However, the increase in HCl-P_i and residual P of the soils was more predominant at high temperature (650°C). The study suggested that biochar pyrolyzed at 300–450°C could be used to increase P bioavailability in tropical soils.     

Short-term effects of biochar amendment on soil microbial community in humid tropics

Biochar is known to ameliorate soil fertility and improve crop production but information regarding soil microbiota responses on biochar amendment remains limited. The experiment was conducted to study the effect of biochars from palm kernel (pyrolysed at 400°C) and rice husk (gasified at 800°C) in a sandy loam Acrisol from Peninsular Malaysia. The soil was amended with palm kernel shell biochar (PK), rice husk biochar (RH), palm kernel biochar with fertilizer (FPK), rice husk biochar with fertilizer (FRH), fertilizer and control soil. Soil samples were taken during maize harvesting and were analysed for physico-chemical properties, microbial biomass, microbial abundance and microbial diversity. Increase in pH, moisture content, CEC, organic C, and labile C were recorded in all biochar amended soils. Microbial biomass C was 65% and 36% higher in RH and FRH, respectively, than control. Microbial biomass N was greatest in FPK and FRH with respective increment of 359% and 341% than control. β-glucosidase and xylanase activities were significantly increased in all biochar treated soils than control. A shift in microbial diversity was not detected. The biochar affects the microbial community by altering the soil environment and increasing labile active carbon sources in the short-term amendment.     

Bagasse Ash Application Stimulates Agricultural Soil C Sequestration Without Inhibiting Soil Enzyme Activity

Disposal of ashes from agro-industrial waste has become an important issue that can cause serious environmental problems. These materials may be used in agriculture for soil fertility improvement and carbon sequestration. The effect of applying bagasse ash (BA), rice husk ash (RHA), and RHA mixed with fly ash (MA) to wheat was evaluated on soil organic carbon (SOC) and microbial activity in a loamy sand soil after four years of wheat-rice cropping. BA application resulted in C accrual at 525 kg ha^?1 y^?1 in soil, whereas RHA and MA did not have a significant effect. BA increased coarse particulate (cPOC) and mineral-associated organic matter (MinOC) and extractable C pools viz. hot water soluble, potassium permanganate (KMnO₄)-oxidizable, easily oxidizable, non-oxidizable, and microbial biomass C. BA application also improved overall microbial and oxidative activity and stimulated fluorescein diacetate (FDA), dehydrogenase, and cellulase enzyme activities in soil. Application of RHA though did not lead to net C sequestration, yet it increased dehydrogenase and cellulase activities. Compared to unamended soil, MA application increased MinOC and FDA activity in soil. After 4 years of their application, none of the ashes adversely influenced soil biological activity expressed in terms of enzyme activities suggesting that these ashes can be disposed to agricultural soils. However, effects of their long-term application on soil biological processes need to be further investigated.     

Growth and yield response of lettuce to irrigation and growth media from composted sawdust and rice husk

In sub-Saharan Africa, manure and loam soil are popular growing media substrates. However, their poor physiochemical properties limit their use in growing media. Following a survey of farmers, single species sawdust, mixed species sawdust, and rice husk (RH) were selected and composted with poultry manure. Additionally, the RH was charred for use in soilless media. Objectives were to produce feedstock-specific composts and determine appropriate proportion for using them in containerized systems. Three composts produced were amended with soil in ratios of 1:1, 1:2, and 1:3 (v/v) in an initial experiment. In a second experiment (soilless), the single sawdust and RH compost were each amended with RH biochar in ratios of 1:0, 1:1, 1:2 (v/v) and subjected to half or full pot irrigation. RH compost amended soils gave the highest lettuce yield. In the soilless media, 2:1 ratio (v/v) of biochar to sawdust compost gave the highest yield.     

Aggregate-associated soil organic carbon and total nitrogen following amendment of puddled and sawah-managed rice soils in southeastern Nigeria

Puddling during sawah rice cultivation destabilizes the soil structure. The re-formation of soil water-stable aggregates (WSA) following puddling and amendments, and their associated organic carbon (SOC) and total N were studied at Akaeze and Ikwo in south-eastern Nigeria. The amendments, which were randomized in triplicate, include control, NPK fertilizer, poultry dropping, rice husk powder and rice husk ashes (RHA). Soil samples from 0 to 15 cm depth were taken from the field after 2 years of cultivation. Most of the SOC were found in the very fine aggregates. There was no consistent trend in the treatment effects. However, the NPK-amended soils showed the lowest values of WSA > 2 mm in both locations, whereas the poultry dropping-amended soils showed the least and the highest mean-weight diameter (MWD) values at Akaeze and Ikwo, respectively. The SOC of the whole soil in Akaeze correlated positively with MWD (r = 0.92*). Irrespective of location, SOC in soils and WSA > 2.00 mm correlated positively with MWD (r = 0.56*; 0.65*, respectively) while SOC in WSA 0.50–0.25 mm accounted for low MWD values. More carbon was sequestered at Akaeze than at Ikwo, with the RHA-amended soils being the highest at both locations.     

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.     

Changes in Chemistry of Rice Husk Compost and Its Effect on Negative Charge and Nutrient Content of a Chemically Degraded Oxisol

Rice husk application and its long-term effects on charge characteristics and elemental composition of a chemically degraded Oxisol have not been rigorously studied. The objective of the study was to determine the ability of composted rice husk (CRH) to preserve organic carbon (C), generate negative charge, and release various ions in heavy clay Oxisol. The topsoil and subsoil, representing natural and erosion conditions, respectively, were incubated with CRH for 24 months. Results showed carbon types of CRH, as revealed by solid-state cross-polarization magic angle spinning ¹³C nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy, were relatively unchanged from months 5 to 12 after incubation, indicating limited decomposition. Carbon types were dominated by O-alkyl and di-O-alkyl C with small proportions of alkyl, methoxyl, aromatic, phenolic, and carboxyl C. After 24 months of incubation, O-alkyl and di-O-alkyl C decreased, indicating susceptibility, whereas alkyl, methoxyl, aromatic, and phenolic C increased, indicating resistance to decomposition. Values of pH₀ and point zero net charge (PZNC) were measured using potentiometric titration and ion adsorption indices, respectively. Values of pH₀ and PZNC decreased during CRH incubation for both topsoil and subsoil, suggesting the increase of soil negative charge. Total negative charge for topsoil and subsoil increased from 2.7 to 3.5 cmol_c/kg and 2.5 to 3.2 cmol_c/kg, respectively. This reflects that CRH was able to mask soil positive charge to increase negative charge. In situ soil solution study indicated CRH could release various elements in the order of potassium (K) > sulfur (S) > natrium (Na) > silicon (Si) > magnesium (Mg) > calcium (Ca). In addition, toxic elements, aluminum (Al) and manganese (Mn), were significantly suppressed. The implication of the study is that CRH offers a means to increase cation exchange capacity and nutrient content of highly weathered soils while preserving organic C, thereby reducing CO₂ emission from agriculture.     

Organic amendments decomposability influences microbial activity in saline soils

Organic amendments with contrasting biochemical properties were investigated by conducting an incubation experiment in soils irrigated with different levels of saline water. Soil samples were taken from a long-term experimental field plots irrigated with normal water and saline water having electrical conductivity (EC) 6 and 12 dS m^?1, respectively. Finely ground biochar, rice straw (RS), farm yard manure (FYM) and glucose were added at two rates (1% and 2.5% carbon basis) and incubated for 8 weeks at 25°C. Cumulative respiration (CR), microbial biomass carbon and available nutrients (nitrogen and phosphorus) were negatively correlated with EC, irrespective of the source and amount of added carbon (C). Compared with non-saline soil, at EC 12, relative decrease in CR was lowest with glucose (21.0%) followed by RS (32.0%), FYM (46.0%) and biochar (55.0%). Dissolved organic carbon was positively correlated with salinity and its concentration was higher in treatments with higher rate of C addition (2.5% C). This study showed decomposability of organic amendments and their rate of addition determines microbial activity in saline soils. Further, lower nitrogen (N) release from amendments under saline conditions limits microbial ability to utilize available C for satisfying their energy needs.     

Microbial activity and metabolic quotient of microbes in soils amended with biochar and contaminated with atrazine and paraquat

The study was conducted to determine how biochar as a soil amendment maintained the microbial community in pesticide contaminated soils. Alfisol (Adenta series – Typic Kandiustalf) and Vertisol (Akuse series – Typic Calciustert) were amended with biochar (0 t/ha biochar, 10 t/ha cocoa husk biochar (CHB), 10 t/ha rice husk biochar (RHB)) and pesticides (atrazine and paraquat at two rates each namely 0 kg/ha pesticide and 10 times the normal recommended rate of pesticide) were applied. The CHB-amended soils stimulated microbial activities such as ammonia and nitrate release more than the RHB-amended soils. Basal respiration was significantly higher in the atrazine polluted soils than in paraquat polluted soil. Significant interaction occurred between soil type and biochar and high microbial biomass carbon was recorded for vertisol amended with CHB. Metabolic quotient was lower in soils amended with biochar and polluted with atrazine than in the un-amended soil. The use of CHB in soil of high clay content (47.5%, i.e. the vertisol) was a more effective management tool in maintaining the microbial community in a pesticide-polluted environment than in soil of lower clay content (22.5%). Soils of high clay content amended with biochar can sustain the soil microbial community even in a disturbed environment.     

生物炭-凹凸棒土复合材料对水稻土锌镉的钝化及土壤养分和酶活性的影响研究

为了比较生物炭、凹凸棒土以及生物炭-凹凸棒土复合材料3种钝化剂对锌镉复合污染水稻土的钝化修复效果,本研究利用傅立叶红外光谱(FT-IR)、X射线衍射(XRD)、比表面积表征(BET)和扫描电镜(SEM)等技术手段对稻壳生物炭和凹凸棒土样品进行表征,并采用土培试验研究稻壳生物炭、凹凸棒土及生物炭-凹凸棒土复合材料对实际重金属锌(Zn)、镉(Cd)污染水稻土钝化效果及理化性质的影响。结果表明,凹凸棒土比稻壳生物炭具有更大的比表面积,且表面更不规则、更粗糙。土培试验表明,3种钝化剂均降低了水稻土中Cd和Zn的生物有效性,并在不同程度上改善了土壤理化性质。单独添加2.0%凹凸棒土和2.0%稻壳生物炭处理,分别使土壤Zn有效态含量降低了86%和51%,Cd有效态含量降低了25%和8%。2.0%生物炭-凹凸棒土复合材料施加后,土壤中Zn和Cd有效态含量分别降低了83%和23%,且土壤pH值提高至5.8,有机碳含量提高了39%。说明稻壳生物炭-凹凸棒土复合材料比单独使用凹凸棒土和生物炭更能有效地固定Cd和Zn,同时能改善复合污染水稻土的理化特性。因此,生物炭-凹凸棒土复合材料具有作为一种新型钝化材料用于土壤修复的潜力,为土壤重金属原位钝化修复提供了一种新思路。     

Influence of Long‐Term Sodic‐Water Irrigation,Gypsum, and Organic Amendments on Soil Properties and Nitrogen Mineralization Kinetics under Rice–Wheat System

Abstract

Influence of long‐term sodic‐water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice–wheat cropping in a sandy loam soil in northwest India. Long‐term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg^?1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW‐irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS‐amended plots but increased it under GM‐treated, FYM‐treated, or unamended plots. Nitrogen mineralization potential (N_o) ranged from 62 to 543 mg N kg^?1 soil. In the first‐order zero‐order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg^?1 soil. Compared to the first‐order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in N_o were influenced more by changes in pH, SAR, and ESP induced by long‐term SW irrigations and amendments rather than by soil OC.     

稻壳基生物炭对生菜Cd吸收及土壤养分的影响

探讨稻壳基生物炭对Cd污染土壤上叶菜吸收Cd和土壤Cd形态的影响作用,明确稻壳基生物炭对土壤Cd污染的调控效应,可为合理利用稻壳基生物炭降低叶菜Cd含量提供参考。采用盆栽试验,研究了稻壳基生物炭在不同用量水平下对2茬生菜地上部Cd含量、土壤养分含量及Cd赋存形态的影响。结果表明,在5~25 g-kg-1用量范围内,稻壳基生物炭显著降低了2茬生菜地上部和根系Cd含量,且在最大用量25 g-kg-1时效果最好,地上部Cd含量分别比未施稻壳基生物炭的对照处理降低了19.6%和45.8%,根系Cd含量分别降低了36.8%和28.0%。在25 g-kg-1用量水平下,稻壳基生物炭对土壤p H、有效磷、速效钾及有机质含量提升效果明显,但显著降低了土壤碱解氮含量。施加稻壳基生物炭对土壤有效态Cd含量及Cd化学形态也有不同影响。随着稻壳基生物炭用量的增加,土壤NH4OAc提取态Cd含量和弱酸提取态Cd含量显著降低,在用量为25 g-kg-1时,分别比对照降低17.9%和10.4%,可还原态Cd含量无显著变化,可氧化态Cd含量呈减低趋势,残渣态Cd含量增加17.6%。因此推测,提升土壤p H、降低土壤有效态Cd含量、增加残渣态Cd含量可能是稻壳基生物炭降低生菜体内Cd含量的主要原因。稻壳基生物炭可以作为土壤改良剂,抑制Cd污染土壤上叶菜对Cd的吸收,改善土壤养分状况。     

Modeling a long-term effect of rice straw incorporation on SOC content and grain yield in rice field

ABSTRACT

The long-term effects of rice straw incorporation on soil organic carbon (SOC) content and rice yield were evaluated from rice cultivation with different treatments: no rice straw (control), rice straw (RS), and rice straw compost (RSC) as a main-plots; five levels of nitrogen (N) fertilizer application: 0, 100, 150, 200, and 250 of N (kg ha^?1) as a sub-plots. The denitrification and decomposition (DNDC) model was employed to simulate changes in SOC content and rice grain yield over 35 years. Additionally, scenario analysis on continuous or discontinuous RS incorporation in rice fields was conducted using the DNDC model. The long-term results indicated that RS and RSC treatments played a crucial role in increasing grain yields by 9% and 11% due to the increased SOC contents compared to control treatment. The validated DNDC model on SOC contents and yields showed a good agreement between the observed and simulated values based on the normalized root mean square errors. The model predicted a rapid decline of SOC contents without RS incorporation. Results suggested that incorporating rice straw or amending manure to paddy soils is a preferred practice for maintaining SOC contents.     

Characterization of biochar and their influence on microbial activities and potassium availability in an acid soil

Application of biochar to soil has increased considerably during recent years because of its effectiveness as a soil amendment causing beneficial effects on soil health. However, the effects have been reported to vary and depend upon types of feedstock and pyrolysis conditions during biochar production. Therefore, characterization of biochar is extremely important for its efficient utilization as a soil amendment. In the present study, biochar was prepared from agro-industrial by-products (rice husk and sugarcane bagasse) and weeds (Parthenium and Lantana) under similar pyrolysis conditions. Lantana biochar (LBC) showed the highest pH (10.4) while the lowest value (8.5) being recorded in rice husk biochar (RHBC). The energy-dispersive X-ray spectroscopy (EDS) analysis indicated that LBC and Parthenium biochar (PBC) were superior with respect to potassium (K) content than sugarcane bagasse biochar (SBBC) and RHBC. The Fourier-Transform Infrared Spectroscopy (FTIR) study exhibited the existence of different functional groups in biochar. All the biochar treated soils showed significantly higher microbial activities with different degrees. Application of LBC and PBC at 4.50 g kg^?1 soil significantly increased K availability in soil. Lantana biochar and PBC amended the soil at 9 g kg^?1 significantly increased the soil pH thus makes these biochar as potential liming materials.     

Total organic carbon and its composition in long-term field experiments in the Czech Republic

Abstract

Total organic carbon content and its composition have been evaluated in the topsoil in the selected plots of 13 long-term field experiments conducted in different soil and climate conditions. The altitude of the sites ranged from 225 – 670 m above sea level. Four variants of the organic and mineral fertilization were selected in each experiment: Nil, which did not receive any organic or mineral fertilizers since the beginning of the experiment, mineral fertilized variant NPK, organic fertilized (manured) variant FYM and both organic and mineral fertilized variant FYM + NPK. Total organic carbon (C) content in the topsoil differed as a result of the soil and climate conditions (it ranged from 0.96 – 1.80% C in the Nil variants) and due to the organic and mineral fertilization. The inert and decomposable part of the soil organic C content was calculated and the hot water soluble carbon content was determined. Relationships between the individual SOM fractions have shown a highly significant correlation, except for the decomposable C calculated as a difference to Nil variant.     

Effects of Rice Husk Ash and Bagasse Ash on Phosphorus Adsorption and Desorption in an Alkaline Soil under Wheat–Rice System

Rice husk ash (RHA) and bagasse ash (BA) are available in large quantities in South Asian countries growing rice and sugarcane. Land application of RHA and BA is likely to influence chemistry of soil phosphorus (P) and thereby P adsorption and desorption. Laboratory studies were carried out to investigate the short-term and long-term effects of RHA and BA application on P adsorption and desorption in an alkaline soil under a wheat–rice system. Addition of RHA or BA (10 Mg ha^?1) resulted in a significant decrease in P adsorption compared to the control. The decrease in P adsorption was lower when RHA and BA were applied to either rice or wheat as compared with when applied to both the crops. The BA was more effective in reducing P adsorption than RHA because of its greater P concentration. Fresh addition of RHA and BA at 1% (dry-weight basis) showed a small effect on P adsorption as compared to their long-term application. The Frendulich isotherm equation gave better fit with the experimental data than the Langmuir equation and is reliable to describe the P quantity/intensity relationships of this soil as affected by the additions of RHA and BA. The P-adsorption capacities (revealed from the Langmuir isotherms) of the unamended control, RHA, and BA (applied to both wheat and rice) were 256, 313, and 385 mg kg^?1, respectively; the corresponding bonding energies for the three treatments are 0.0085, 0.0041, and 0.0026 L kg^?1, respectively. Desorption of P was minimum in the control plots and maximum with BA followed by RHA, especially when applied to both the crops.     

Effects of single and successive applications of rice husk charcoal on paddy soil carbon content and rice productivity during two cropping seasons

A two-year field experiment was conducted to evaluate residual and cumulative effects of rice husk charcoal (RC) application on physicochemical soil properties and rice productivity in an Andosol paddy field. Three RC application rates, 10, 20, and 40 Mg ha^?1, one rice husk (RH) application rate of 20 Mg ha^?1, and a control with no application of RC or RH were laid out in the first year of the experiment. In the second year, the experimental plot was divided into halves: one with the same application rates as in the first year (successive applications) and the other without additional RC or RH (single application). Significant impacts of RC application were observed from the first year on soil bulk density, porosity, carbon (C) content, and carbon-to-nitrogen (C/N) ratio. Soil C content was directly proportional to the amount of RC application over the 2 years showing that the C derived from RC was markedly recalcitrant in soil compared to that from RH. The increased C was present not only in the plow layer but also spread over the top 20 cm of paddy field. As compared to the control, successive RC applications at 20 Mg ha^–1 increased soil C contents by 12.7 g kg^–1 and 14.4 g kg^–1 in the 0–10 cm and 10–20 cm layers after two rice seasons, respectively. Successive RC applications significantly increased straw weight and panicle number, partly due to the increased Si uptake by rice plants. However, grain yield did not significantly differ among the treatments because RC application decreased 1000-grain weight. We speculate that the reduction in 1000-grain weight may be due to immobilization of available N at the reproductive stage under high soil C/N ratio conditions. This suggests the need for N fertilizer top-dressing to obtain the potential yield in the RC-applied fields. Furthermore, the diminishing residual effects of RC application on the rice growth and yield parameters in the second season suggest that successive, or applications at an interval of 2–3 years, would be required to maintain the higher Si deposits in plants, thereby sustaining rice productivity.     

Microbial Activity Is Constrained by the Quality of Carbon and Nitrogen under Long-term Saline Water Irrigation

Most important, yet least understood, question, how microbial activity in soil under saline water irrigation responds to carbon (C) varying qualitatively (most labile form to extreme recalcitrant form) with or without maintaining C/N ratio was investigated in an incubation experiment. Soil samples from a long-term saline-water (electrical conductivity, EC ≈ 0, 6, and 12 dS m^?1)- irrigated field were incorporated with three different C substrates, viz., glucose, rice straw (RS), and biochar with or without nitrogen (N as ammonium sulfate, NH₄SO₄) and were incubated at 25 °C for 56 days. Cumulative respiration (CR), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and dehydrogenase activity (DEA) concentrations decreased with increasing EC (P < 0.05), but less so in soils amended with glucose followed by RS and biochar. The addition of N to soils amended with different C substrates significantly decreased CR, MBC, DEA, and available phosphorus (P) concentrations at a given EC level.     

利用稻壳炭提高复合肥料在土壤中的磷素有效性

[目的]研究稻壳炭添加对复合肥料在土壤中磷素有效性的影响,旨在为养分高效、环境友好型复合肥料的开发提供科学依据.[方法]以磷酸一铵(MAP)、磷酸二铵(DAP)、硝酸磷肥(NP)和聚磷酸铵(APP)为磷源,设置0、5％、10％3个稻壳生物炭加入量,与尿素、氯化钾、石粉以及其他辅料制作N-P2O5-K2O比例为15-10...