Effect of the long-term application of organic matter on soil carbon accumulation and GHG emissions from a rice paddy field in a cool-temperate region,Japan. -I. Comparison of rice straw and rice straw compost -

ABSTRACT

The influence of the long-term combination of rice straw removal and rice straw compost application on methane (CH₄) and nitrous oxide (N₂O) emissions and soil carbon accumulation in rice paddy fields was clarified. In each of the initial and continuous application fields (3 and 39?51 years, respectively), three plots with different applications of organic matter were established, namely, rice straw application (RS), rice straw compost application (SC) and no application (NA) plots, and soil carbon storage (0?15 cm), rice grain yield and CH₄ and N₂O fluxes were measured for three years. The soil carbon sequestration rate by the organic matter application was higher in the SC plot than in the RS plot for both the initial and continuous application fields, and it was lower in the continuous application field than in the initial application field. The rice grain yield in the SC plot was significantly higher than those in the other plots in both the initial and continuous application fields. Cumulative CH₄ emissions followed the order of the NA plot < the SC plot < the RS plot for both the initial and continuous application fields. The effect of the organic matter application on the N₂O emissions was not clear. In both the initial and continuous application fields, the increase in CH₄ emission by the rice straw application exceeded the soil carbon sequestration rate, and the change in the net greenhouse gas (GHG) balance calculated by the difference between them was a positive, indicating a net increase in the GHG emissions. However, the change in the GHG balance by the rice straw compost application showed negative (mitigating GHG emissions) for the initial application field, whereas it showed positive for the continuous application field. Although the mitigation effect on the GHG emissions by the combination of the rice straw removal and rice straw compost application was reduced by 21% after 39 years long-term application, it is suggested that the combination treatment is a sustainable management that can mitigate GHG emissions and improve crop productivity.     

Changes in natural 15N abundance in paddy soils under different,long-term soil management regimes in the Tohoku region of Japan

Abstract

Long-term temporal changes in natural ¹⁵N abundance (δ¹⁵N value) in paddy soils from long-term field experiments with livestock manure and rice straw composts, and in the composts used for the experiments, were investigated. These field experiments using livestock manure and rice straw composts had been conducted since 1973 and 1968, respectively. In both experiments, control plots to which no compost had been applied were also maintained. The δ¹⁵N values of livestock manure compost reflected the composting method. Composting period had no significant effect on the δ¹⁵N value of rice straw compost. The δ¹⁵N values increased in soils to which livestock manure compost was successively applied, and tended to decrease in soils without compost. In soils to which rice straw compost was successively applied, the δ¹⁵N values of the soils remained constant. Conversely, δ¹⁵N values in soils without rice straw compost decreased. The downward trend in δ¹⁵N values observed in soils to which compost and chemical N fertilizer were not applied could be attributed to the natural input of N, which had a lower δ¹⁵N value than the soils. Thus, the transition of the δ¹⁵N values in soils observed in long-term paddy field experiments indicated that the δ¹⁵N values of paddy soils could be affected by natural N input in addition to extraneous N that was applied in the form of chemical N fertilizers and organic materials.     

Use of mineralization kinetics to estimate the potentially mineralizable nitrogen of rock phosphate-enriched composts-amended soil

Predicting nitrogen (N) mineralization has been one of the greatest challenges to improving N management in agriculture. A laboratory incubation experiment was conducted to study the N mineralization of soil amended with rock phosphate (RP)-enriched composts. The RP-enriched rice straw compost amended soil mineralized highest N as compared to compost prepared from mustard stover and tree leaves. The first-order model was found to be the most suitable for N because it provided the best fit to the experimental data and for its simplicity. The model predicted that potentially mineralized N (N₀) was varied from 4.0 to 52.1 mg kg^?1 and the mineralization rate k varied from 0.015 to 0.066 day^?1. The rice straw compost amended soil had higher N₀ value than mustard stover and tree leaves compost amended soil. This study demonstrated the importance of application of rock phosphate-enriched composts in improving N supplying capacity of soil.     

Methane and nitrous oxide emissions as affected by organic–inorganic mixed fertilizer from a rice paddy in southeast China

Purpose

The effects of commercial compost fertilizer application on trace gas emissions are not well understood due to a lack of field experiments. The objective of this study was to evaluate the emissions of methane (CH₄) and nitrous oxide (N₂O) along with grain yield from a rice paddy as affected by different organic–inorganic mixed fertilizer (OIMF) treatments.

Materials and methods

A field experiment was initiated in 2006 with chemical compound fertilizer (CF) and three OIMF amendments including pig manure compost (PMC), Chinese medicine residue compost (CMC), and rapeseed cake compost (RCC), from a rice paddy in southeast China. The emissions of CH₄ and N₂O were simultaneously measured using the static opaque chamber method over the entire rice growing season in 2011. Soil biotic parameters were measured in soil collected after the rice was harvested in 2011.

Results and discussion

Relative to the control, the OIMF treatments significantly increased CH₄ emissions by 56–99 %, mainly due to exogenous organic substrate input, whereas no difference was observed in the CF treatment. The N₂O emissions were stimulated substantially by an average of 40 % due to nitrogen fertilization compared with the control. Consecutive OIMF application tended to increase the grain yield, making it marginally higher than that of the CF treatment (7 %, P?=?0.06). Compared with the control, the CF treatment slightly decreased the global warming potential and greenhouse gas (GHG) intensity, while they were remarkably increased in the OIMF treatments. Over the 5-year period of 2006–2011, the annual soil carbon sequestration rate was estimated to be 1.19 t C ha^?1 year^?1 for the control and 1.73–1.98 t C ha^?1 year^?1 for the fertilized treatments.

Conclusions

Our results suggest that despite the beneficial effects of increasing both grain yield and soil organic matter, OIMF application such as PMC, CMC, and RCC may be responsible for increased global warming due mainly to the stimulated CH₄ emissions. This effect should be thus taken into account when balancing agricultural production and GHG mitigation.     

Application rate and composting method affect the immediate and residual manure fertilizer value in a maize–rice–rice–maize cropping sequence on a degraded soil in northern Vietnam

A field experiment was carried out in northern Vietnam to investigate the effects of adding different additives [rice (Oriza sativa L.) straw only, or rice straw with added lime, superphosphate (SSP), urea or a mixture of selected microorganism species] on nitrogen (N) losses and nutrient concentrations in manure composts. The composts and fresh manure were applied to a three-crop per year sequence (maize–rice–rice) on a degraded soil (Plinthic Acrisol/Plinthaquult) to investigate the effects of manure type on crop yield, N uptake and fertilizer value. Total N losses during composting with SSP were 20% of initial total N, while with other additives they were 30–35%. With SSP as a compost additive, 65–85% of the initial ammonium-N (NH₄-N) in the manure remained in the compost compared with 25% for microorganisms and 30% for lime. Nitrogen uptake efficiency (NUE) of fresh manure was lower than that of composted manure when applied to maize (Zea mays L.), but higher when applied to rice (Oriza sativa L.). The NUE of compost with SSP was generally higher than that of compost with straw only and lime. The mineral fertilizer equivalent (MFE) of manure types for maize decreased in the order: manure composted with SSP?>?manure composted with straw only and fresh manure?>?manure composted with lime. For rice, the corresponding order was: fresh manure?>?manure composted with SSP/microorganisms/urea?>?manure composted with lime/with straw alone. The MFE was higher when 5 tons manure ha^?1 were applied than when 10 tons manure ha^?1 were applied throughout the crop sequence. The residual effect of composted manures (determined in a fourth crop, with no manure applied) was generally 50% higher than that of fresh manure after one year of manure and compost application. Thus, addition of SSP during composting improved the field fertilizer value of composted pig manure the most.     

Changes in soil nutrient content and bacterial community after 12 years of organic amendment application to a vineyard

An interesting alternative to landfills for disposing of organic residues is their addition to soil as composted organic residues. There is little information available about the long‐term benefits following prolonged periods of application. After 12 years of annual incorporation of organic amendments to the soil of a vineyard, three soil characteristics were analysed: mineral content, bacterial community and soil greenhouse gas (GHG) emissions. The organic amendments were (i) a pelletized organic compost (PEL) made from plant, animal and sewage sludge residues, (ii) a compost made from the organic fraction of municipal solid waste (OF‐MSW) and (iii) a stabilized sheep manure compost (SMC). Mineral fertilizer (NPK) and an unaltered control treatment were also included. Our results showed that long‐term application of treated residues as compost changed soil nutrient content, bacterial community and gas emission rates. For instance, SMC increased nutrients and soil organic matter (OM) throughout the experiment. There was a change in bacterial community structure, with an increase in the phylum Proteobacteria observed for all four treated soils, and an increase in the phylum Bacteroidetes for PEL, OF‐MSW and SMC treatments. Among the organically‐amended soils, the amount of Adhaeribacter increased by a factor of 2.5 times more than the control, which reported a total of 2.0% of the bacterial community compared with 5.6% for PEL, 5.2% for OF‐MSW and 5.0% for SMC. Adhaeribacter may be a genus that specializes in the degradation of residues in the different composts. The SMC treatment had the largest Chao1 estimator and was the most biodiverse of all treatments. These changes in bacterial community structure did not correlate with the observed GHG fluxes from the sampling day. The application of amendments did not affect N₂O fluxes. However, the application of treatments slightly reduced the capacity for CH₄ sequestration by soil with respect to the untreated soils. Compost is an effective method to increase soil fertility. Soil GHG emissions should be further evaluated.     

不同秸秆还田年限对稻麦轮作系统温室气体排放的影响

为揭示稻麦轮作系统不同秸秆还田年限下温室气体排放特征及减排调控机制,本研究采用大田小区试验,考察了稻麦轮作不同秸秆还田年限[空白对照(CK)、常规处理秸秆不还田(NT)、1年秸秆还田(SR1)和5年秸秆还田(SR5)]对CH4、CO2和N2O 3种温室气体排放规律的影响,同时测定了土壤固碳量,估算了秸秆焚烧产生的温室气体排放量,综合计算了4种处理对全球变暖的贡献。试验结果表明,SR1和SR5均显著提升CH4和CO2的排放通量,分别高出NT、CK处理73.52%、309.49%和13.29%、13.06%;同时显著降低N2O排放通量,较NT降低29.68%和42.55%;但SR1和SR5之间温室气体排放通量差异不显著;与NT相比,SR1和SR5可以显著提高土壤固碳量517.9%和709.03%,SR5土壤固碳量高出SR1达30.93%;NT秸秆焚烧产生的全球气温变暖贡献为9 698.49 kg(CO2-eqv)·hm?2,比CK高126.98%。综合分析温室气体排放、土壤固碳以及秸秆焚烧3个因素,SR1全球升温贡献最低,显著低于NT 4.72%。短期全量秸秆还田有助于降低总体温室气体排放,长期进行秸秆还田后降低幅度会逐步减小。     

Reduction in greenhouse gas emissions by no-tilling rice cultivation in Hachirogata polder,northern Japan: Life-cycle inventory analysis

Abstract

The scenarios for conventional puddling and no-tilling rice (Oryza sativa L.) cultivation were compared in terms of greenhouse gas (GHG) emissions from paddy fields, fuel consumption and manufacturing of invested materials using a life cycle inventory (LCI) based analysis. Only the differences between the scenarios were examined. The no-tilling scenario omitted both tilling and puddling, but included spraying of a non-selective herbicide and used a transplanter equipped with a rotor. Fertilization was a basal single application of controlled release fertilizer in nursery boxes for all scenarios. After transplanting, there were no differences in machine work, invested materials or rice yields between the scenarios. The no-tilling scenario saved on fuel consumption, totaling carbon dioxide (CO₂) output of 42 kg ha^?1, which was equal to the 6% reported GHG emissions from fuel consumption by operating machines during rice production in Japan. Methane (CH₄) and nitrous oxide (N₂O) emissions from the paddy fields were also monitored and compared for the scenarios. Methane has a major effect on global warming as part of the GHG emitted from paddy fields. The cumulative CH₄ emissions from the no-tilling cultivation were 43% lower than those from conventional puddling cultivation because the plow layer was more oxidative in no-tilling cultivation. The N₂O emissions were not significantly different between the cultivation scenarios. There were no significant differences in soil respiration, soil carbon contents or straw yields between the cultivation scenarios. The effect of tillage on CO₂ flux in the paddy fields did not seem to be significant in this study. Consequently, the GHG emissions from the no-tilling field counted as CO₂ using global warming potentials were 1,741 kg CO₂ ha^?1 lower than those from the conventional puddling field. In conclusion, no-tilling rice cultivation has the potential to save 1,783 kg CO₂ ha^?1 calculated using the sum of fuel consumption and GHG emissions from paddy fields. No-tilling rice cultivation is considered to be environmentally friendly agriculture with respect to reducing GHG emissions.     

Effect of Woody Peat as an Additive on Maturity and Gaseous Emissions During Pig Manure Composting

Woody peat was used as an additive to compost with pig manure in 1.2 m³ composting reactors under aerobic conditions for a 77?days period to estimate the effect on the compost maturity and gaseous emissions (NH₃, N₂O, and CH₄). Pig manure was also composted with cornstalks (the traditional method) as a control treatment. The results showed that both cornstalks and woody peat composts reached the required maturity standard. Composting with woody peat as a bulking agent was found to reduced NH₃ emissions by 36% than the cornstalks amended treatment. Although CH₄ emission increased by adding woody peat, N₂O emission was considerably reduced, resulting in a slight decrease in total greenhouse gas emissions. More importantly, woody peat could reduce the losses of total carbon and total nitrogen, improve the compost quality as fertilizer.     

Influence of water depth and soil amelioration on greenhouse gas emissions from peat soil columns

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO₂ emissions. No significant difference was observed in the CH₄ emissions in response to water depth and amelioration. The ameliorations influenced the CO₂ and N₂O emissions from the peat soil. The application of biochar+compost enhanced the CO₂ and N₂O emissions but reduced the CH₄ emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO₂ and N₂O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO₂, CH₄ and N₂O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.     

Co-incorporation of rice straw and leguminous green manure can increase soil available nitrogen (N) and reduce carbon and N losses: An incubation study

Returning rice straw and leguminous green manure alone or in combination to soil is effective in improving soil fertility in South China. Despite the popularity of this practice, our understanding of the underlying processes for straw and manure combined application is relatively poor. In this study, rice straw (carbon (C)/nitrogen (N) ratio of 63), green manure (hairy vetch, C/N ratio of 14), and their mixtures (C/N ratio of 25 and 35) were added into a paddy soil, and their effects on soil N availability and C or N loss under waterlogged conditions were evaluated in a 100-d incubation experiment. All plant residue treatments significantly enhanced CO₂ and CH₄ emissions, but decreased N₂O emission. Dissolved organic C (DOC) and N (DON) and microbial biomass C in soil and water-soluble organic C and N and mineral N in the upper aqueous layer above soil were also enhanced by all the plant residue treatments except the rice straw treatment, and soil microbial biomass N and mineral N were lower in the rice straw treatment than in the other treatments. Changes in plant residue C/N ratio, DOC/DON ratio, and cellulose content significantly affected greenhouse gas emissions and active C and N concentrations in soil. Additionally, the treatment with green manure alone yielded the largest C and N losses, and incorporation of the plant residue mixture with a C/N ratio of 35 caused the largest net global warming potential (nGWP) among the amended treatments. In conclusion, the co-incorporation of rice straw and green manure can alleviate the limitation resulting from only applying rice straw (N immobilization) or the sole application of leguminous green manure (high C and N losses), and the residue mixture with a C/N ratio of 25 is a better option because of lower nGWP.     

Mitigating methane emissions from irrigated paddy fields by application of aerobically composted livestock manures in eastern China

Livestock manure heaps and wetland rice fields are major sources of CH₄ emissions. A field experiment with an associated composting study were undertaken to investigate CH₄ emissions during manure composting and subsequent land application on paddy. Over a 24‐day period in the composting experiment, CH₄ emissions from stored manure was 17 times higher than that from composting manure, indicating that composting as an aerobic process was effective in mitigating CH₄ emissions compared with manure storage, which is normally under an anaerobic environment. Stored and composted manures were subsequently applied as organic fertilizers in the field experiment. Compared with the non‐fertilized control treatment, stored and composted manures increased grain yields by 30% and 21%, respectively. During the full rice‐growing season, the cumulative CH₄ emission was 15.8 g CH₄/m² with the application of composted manure, only one‐third of that from stored manure. CH₄ emission per unit of grain yield was significantly decreased by composted manure, with a reduction of 56% from the control and 73% from stored manure. The results indicate that composted livestock manure in rice cultivation is a triple‐win option through sustaining rice yield, mitigating CH₄ emissions and re‐utilizing livestock waste.     

农业生物质能温室气体减排潜力

中国拥有丰富的农作物秸秆和畜禽粪污等农业废弃物资源。农业生物质能技术是促进农业废弃物资源有效利用的重要途径，既能够解决农业废弃物的环境污染问题、减少因焚烧或无序堆放排放温室气体，又能够替代化石能源减排CO2、提升土壤固碳能力，未来在"双碳"背景下发展潜力很大。该研究基于LCA全生命周期评价方法，研究8种不同生物质能技术的温室气体排放因子，核算农业生物质能转化与利用过程消耗能源的排放、抵扣化石能源减排、副产物土壤碳汇3个方面，并基于秸秆和畜禽粪污两大类农业废弃物资源禀赋及能源化利用潜力，预测3种不同情景下，农业生物质能替代化石能源的潜力，以及减排温室气体的贡献。结果表明，从减排因子看，热解炭气联产和规模化沼气/生物天然气技术的温室气体减排贡献最大。其次为成型燃料、捆烧供暖、生物质发电、炭化和燃料乙醇等技术，而户用沼气的减排贡献相对较小，8种不同生物质能技术的温室气体排放因子分别为-3.47、-3.20、-2.57、-2.63、-2.58、-2.48、-2.42 t/t（单位为标准CO2当量/标准煤当量）；基于现有政策及规划情景、技术水平提升情景、能源需求结构变化情景等3种不同情景下，评价农业生物质能对温室气体减排贡献潜力。结果显示，2030年农业生物质能替代化石能源潜力为6 490×104～7 664×104 t，温室气体减排贡献为1.97×108～2.34×108 t；2060年替代化石能源潜力为9 073×104～10 763×104 t，温室气体减排贡献为2.79×108～3.36×108 t。该研究为实现农业农村领域碳达峰碳中和目标提供数据支撑。     

Estimation of microbial biomass potassium in paddy field soil

Abstract

Potassium (K) in microbial cells, microbial biomass K, in soil has been recently recognized as a K pool for plant growth. We determined soil microbial biomass K in paddy fields to reveal its importance as a K pool in paddy field soil for the first time. Microbial biomass K ranged from 5 to 21 mg K kg^?1 in the soil samples periodically collected from a paddy field and the value corresponded to 41% of the exchangeable K on average. Both microbial biomass K and exchangeable K increased conspicuously due to the long-term application of livestock manure compost or rice straw compost. Biomass K was higher than exchangeable K under K-deficient conditions in the long-term experimental plots without K application. The present study revealed that the microbial biomass contained considerable amounts of K in paddy field soil, indicating the need for evaluation of the microbial biomass K as a source and a stock of K in soil that has been overlooked.     

Impact of biochar addition to soil on greenhouse gas emissions following pig manure application

The application of biochar produced from wood and crop residues, such as sawdust, straw, sugar bagasse and rice hulls, to highly weathered soils under tropical conditions has been shown to influence soil greenhouse gas (GHG) emissions. However, there is a lack of data concerning GHG emissions from soils amended with biochar derived from manure, and from soils outside tropical and subtropical regions. The objective of this study was to quantify the effect on emissions of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) following the addition, at a rate of 18 t ha⁻¹, of two different types of biochar to an Irish tillage soil. A soil column experiment was designed to compare three treatments (n = 8): (1) non-amended soil (2) soil mixed with biochar derived from the separated solid fraction of anaerobically digested pig manure and (3) soil mixed with biochar derived from Sitka Spruce (Picea sitchensis). The soil columns were incubated at 10 °C and 75% relative humidity, and leached with 80 mL distilled water, twice per week. Following 10 weeks of incubation, pig manure, equivalent to 170 kg nitrogen ha⁻¹ and 36 kg phosphorus ha⁻¹, was applied to half of the columns in each treatment (n = 4). Gaseous emissions were analysed for 28 days following manure application. Biochar addition to the soil increased N₂O emissions in the pig manure-amended column, most likely as a result of increased denitrification caused by higher water filled pore space and organic carbon (C) contents. Biochar addition to soil also increased CO₂ emissions. This was caused by increased rates of C mineralisation in these columns, either due to mineralisation of the labile C added with the biochar, or through increased mineralisation of the soil organic matter.     

Soil carbon budget in a single-cropping paddy field with rice straw application and water management based on soil redox potential

Abstract

An ideal state for agroecosystems to mitigate global warming should include both decreasing CO₂ and CH₄ emissions and increasing soil carbon storage. Two-year field experiments were carried out to examine the effects of water management (continuous flooding [CF] and Eh control [EH]) and rice straw management (application [+S] and removal [–S]) on the soil carbon budget in a single-cropping paddy field in Japan. The EH water management based on soil redox potential that the authors have proposed decreased the total CH₄ emission during the rice growing period compared with CF. The +S increased CO₂ emission as soil respiration during the non-flooded fallow period compared with –S, but also increased straw residues in the soil. However, there was little evidence for sequential carbon accumulation in the soil over the year by +S. The resultant annual budget of soil carbon was a loss of 32–103 g C m^?2 in the EH+S treatment compared with a loss of 166–188 g C m^?2 in the CF–S treatment. Taking into account the global warming potentials, the EH+S treatment also decreased the total CO₂-equivalent emission compared with the CF–S treatment. Consequently, a combination of appropriate water management and straw application will be an effective option in decreasing both CO₂-equivalent emission and sustaining soil carbon storage.     

水分含量对水葫芦渣堆肥进程及温室气体排放的影响

水葫芦经挤压处理后,容积减小、干物质含量提高,利于堆肥生产,但目前缺乏相关堆肥条件的研究。本文通过水稻秸秆与水葫芦渣以不同比例混合来调节堆体水分,探讨在65%、70%、75%、80%水分条件下堆肥效果及环境影响,以获得堆肥的最优水分条件。本试验为静态堆肥,动态监测堆体温度、pH值、碳氮养分和温室气体。结果表明,水分对堆体pH、胡敏酸(堆肥7 d)、富里酸无显著影响,对温度、水溶性碳、胡敏酸(堆肥50 d)、凯氏氮、硝态氮、铵态氮影响显著。其中75%水分处理升温能力最佳,堆肥6 d即达最高堆温(53.4℃);50 d时其凯氏氮、硝态氮、铵态氮显著高于65%和70%的水分处理(P<0.05);75%水分处理堆肥50 d与7 d相比,凯氏氮降低最多(21.1%),硝态氮增加最多(434%),铵态氮降低幅度最小(14.1%)。水分对CH4的产生无显著影响;但高水分促进CO2和N2O排放,75%水分处理的CO2排放能量最高,是其他处理的1.9~2.5倍,80%水分处理的N2O排放通量最高,是其他处理的3.9~23.1倍。综合考虑,水稻秸秆与水葫芦渣混合堆肥,堆体水分为75%较为适宜,能兼顾堆肥效率、品质和环境效益。     

Changes in the soil C and N contents,C decomposition and N mineralization potentials in a rice paddy after long-term application of inorganic fertilizers and organic matter

A long-term experiment on combined inorganic fertilizers and organic matter in paddy rice (Oryza sativa L.) cultivation began in May 1982 in Yamagata, northeastern Japan. In 2012, after the 31^st harvest, soil samples were collected from five fertilizer treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha^?1 rice straw (RS), (4) NPK + 10 Mg ha^?1 rice straw compost (CM1), and (5) NPK + 30 Mg ha^?1 rice straw compost (CM3)], at five soil depths (0–5, 5–10, 10–15, 15–20 and 20–25 cm), to assess the changes in soil organic carbon (SOC) content and carbon (C) decomposition potential, total nitrogen (TN) content and nitrogen (N) mineralization potential resulting from long-term organic matter addition. The C decomposition potential was assessed based on the methane (CH₄) and carbon dioxide (CO₂) produced, while the N mineralization potential was determined from the potassium chloride (KCl)-extractable ammonium-nitrogen (NH₄⁺-N), after 2, 4, 6 and 8 weeks of anaerobic incubation at 30°C in the laboratory. Compared to NPK treatment, SOC in the total 0–25 cm layer increased by 67.3, 21.0 and10.8%, and TN increased by 64.2, 19.7 and 10.6%, in CM3, RS and CM1, respectively, and SOC and TN showed a slight reduction in the PK treatment by 5.2 and 5.7%, respectively. Applying rice straw compost (10 Mg ha^?1) instead of rice straw (6 Mg ha^?1) to rice paddies reduced methane production by about 19% after the soils were measured under 8 weeks of anaerobic incubation at 30°C. Soil carbon decomposition potential (Co) and nitrogen mineralization potential (No) were highly correlated with the SOC and TN contents. The mean ratio of Co/No was 4.49, lower than the mean ratio of SOC/TN (13.49) for all treatments, which indicated that the easily decomposed organic matter was from soil microbial biomass and soil proteins.     

Fate of nitrogen derived from 15N-labeled plant residues and composts in rice-planted paddy soil

Pot experiments that lasted for 3 y were conducted to investigate the dynamics of nitrogen derived from plant residues (rice root, hull, straw, corn root, and rapeseed pod-wall), and composts (rice straw compost, cattle manure compost, and cattle manure sawdust compost), which were labeled with ¹⁵N. The rates of nitrogen uptake by rice (=N efficiency), denitrification, and immobilization derived from the organic materials incorporated before the first year of cultivation were investigated throughout 3 y of cultivation. At the end of the first year of cultivation, relatively high rates of N efficiency were obtained for rapeseed pod-wall (24.6%), rice straw (19.1%), and rice hull (18.6%), while corn root and cattle manure sawdust compost displayed a noticeably high denitrification rate. Corn root, cattle manure sawdust compost, rice hull, and rapeseed pod-wall exhibited remarkably high N mineralization rates ranging from 60 to 75% of the organic materials N applied. Cumulative rates of N efficiencies from the organic materials applied before the first year of cultivation fitted well to a first-order kinetic model and their asymptotes were compared among the organic materials. The asymptotic rates of N efficiency tended to depend on the rates at the end of the first year of cultivation.     

Effect of the long-term application of anaerobically digested residual slurry on methane emissions in a rice paddy field

ABSTRACT

The anaerobic digestion of livestock manure is an environmentally compatible technology used for the production of renewable energy. Anaerobically digested residual slurry has been used worldwide as a liquid fertilizer in both upland and paddy fields. However, a controversial question remains as to whether the application of slurry to rice paddy fields increases methane emissions; although methane is one of the most prevalent greenhouse gases, little is known about the effects of the long-term application of residual slurry on methane emission. In this study, we repeatedly applied slurry to a paddy field for six years at different application rates (10, 15, and 20 g N m^?2 based on ammonium-nitrogen content). At the fifth and sixth years of application, we evaluated the effect in terms of methane flux and soil total carbon content. The effect of the long-term application of the slurry (10 g N m^?2) on grain yield was equivalent to that of chemical fertilizer (10 g N m^?2). The application of the residual slurry was likely to increase the cumulative methane emissions during rice growing season in both 2006 and 2007. On the other hand, we observed that soil total carbon did not accumulate significantly in the soil. Thus, we cannot rule out the potential risk of additional methane emissions caused by the application of the residuary slurry to paddy fields.