免耕条件下稻草还田方式对温室气体排放强度的影响

为探讨免耕条件下的稻草高茬和覆盖还田对双季稻田温室气体排放强度(GHGI)的影响,该研究利用静态箱-气相色谱法,对免耕稻草不还田(NWS)、免耕高茬还田(HN)和免耕覆盖还田(SN)3处理稻田GHGI进行了连续2a的观测。结果表明,在各处理水稻产量差异不显著时,双季稻田的GHGI主要由温室气体排放量决定;在稻草用量相同的情况下,2种稻草还田方式均增加了稻田的GHGI,且高茬还田的增加幅度大于覆盖还田,说明高茬还田增强了温室气体通过水稻体内通气组织传输的能力。在20和100a尺度上,甲烷的GHGI均远大于氧化亚氮,在20a尺度上,早稻各处理甲烷的GHGI平均为N2O的109倍,晚稻为14倍,而在100a尺度上,这个倍数有所下降,分别只有35倍和3.77倍,可见,减少甲烷排放是减缓稻田温室气体排放强度的首要目标。在等稻草量的前提下,相比留高茬还田,覆盖还田能有效控制稻田GHGI。该研究可为中国华中地区双季稻田碳增汇和温室气体减排研究提供参考。     

Reduced mineral fertilization coupled with straw return in field mesocosm vegetable cultivation helps to coordinate greenhouse gas emissions and vegetable production

Purpose

The partial substitution of mineral fertilizers with straw in agricultural soils could help to control soil acidification, reduce the risk of eutrophication from agricultural runoff, and increase the utilization efficiency of straw. However, the effects of such coupled practices on greenhouse gas (GHG) emissions and production yields in vegetable fields are not clear. Therefore, the objectives of this study were to (1) understand methane (CH₄) and nitrous oxide (N₂O) emissions in response to the same amounts of straw return with varied amounts of mineral fertilizers, and (2) to identify a solution which could better coordinate GHG emissions, vegetable production yield, and the utilization of agricultural straw following disposal.

Materials and methods

We conducted four-season (lettuce-cabbage-chili-lettuce) vegetable cultivation for 1 year using a control treatment (CT), mineral fertilization only (F), and four mineral fertilization treatments plus maize straw (FS, 0.7FS, 0.6FS, and 0.5FS). We then examined seasonal changes of CH₄ and N₂O fluxes, CH₄ and N₂O cumulative emissions, soil organic carbon (SOC), nitrate nitrogen (NO₃^?-N) and ammonium nitrogen (NH₄⁺-N) content, vegetable yields, global warming potential (GWP), greenhouse gas intensity (GHGI), and N₂O emission factors (EF).

Results and discussion

Compared to the F treatment, the application of maize straw increased the N₂O flux significantly in the FS, 0.7FS, 0.6FS, and 0.5FS treatments. In treatments with added straw, the reduced application of mineral fertilizer led to a reduction in the cumulative N₂O emission; this was due to the reduced content of NO₃^?-N content. The lowest CH₄ flux and cumulative CH₄ emission were observed in the 0.7FS treatment; this may be due to a form of competitive oxidation between CH₄ and NH₄⁺-N from urea. Furthermore, the application of maize straw in combination with a full dose of mineral fertilizers led to high GWP and GHGI values, which showed increases of 88.7% and 78.8%, respectively, in comparison with the F treatment. When taking SOC storage variations into account, which were caused by straw decomposition during cultivation, we identified a negative net GHGI (NGHGI) value (??0.0448 kg CO₂-eq kg^?1 yield) in the 0.7FS treatment. This indicated that the NGHGI had decreased by 116.2% relative to the F treatment when based on similar vegetable yields.

Conclusions

Straw combined with 70% mineral fertilizer led to better GHG emissions and vegetable yield when taking into account the carbon sequestration and decomposition caused by the addition of straw.

     

Effects of rice straw incorporation and N fertilizer on ryegrass yield,soil quality,and greenhouse gas emissions from paddy soil

Journal of Soils and Sediments - Ryegrass is usually rotated with rice in southern China. The influences of returning ryegrass residues on rice yield and soil dynamics have been studied...     

Manipulating the N release from N labelled celery residues by using straw and vinasses

The aim of this laboratory study was to investigate the effect of straw and vinasses on the nitrogen (N) mineralization-immobilization turnover of celery residues during two periods (each simulating a time period from autumn till spring) under laboratory conditions. During the first period (1-198 d), ¹⁵N-labelled celery residues (1.1 g dry matter (DM) kg⁻¹ soil) were incubated together with straw (8.1 g DM kg⁻¹ soil), aiming to immobilize the N released from celery residues, followed by an incorporation of vinasses (1.9 g DM kg⁻¹ soil) after 84 d, with a view to remineralizing the immobilized celery-N. During the second period (198-380 d), the experimental set-up was repeated, except that non-labelled celery residues were used. Total N, mineral N and their ¹⁵N enrichments as well as microbial biomass N were determined at regular time intervals. During both periods, mixing celery residues with straw significantly increased microbial biomass N (90.5 and 40.5 mg N kg⁻¹ extra compared to celery only treatment) and decreased the amount of mineral N (reduction of 56.1 and 45.9 mg N kg⁻¹ soil compared to celery only treatment) and the celery-derived mineral ¹⁵N (0% of mineral celery-derived ¹⁵N in straw treatment compared to 35% of mineral celery-derived ¹⁵N in celery only treatment). After maximum immobilization, a natural remineralization (without addition of vinasses) of 32.2 (at day 198) and 11.1 mg N kg⁻¹ soil (at day 380) occurred in the straw treatment, but the mineral N content remained significantly lower than in the celery only treatment during the complete experiment, and the amount of remineralized celery-¹⁵N was very low (5.4% of celery-derived ¹⁵N after 380 d). Vinasses caused no real priming effect, although it did slightly increase the amount of remineralized celery-¹⁵N (+6.4% of celery-derived ¹⁵N at day 380 compared to the straw treatment), probably due an apparent added N interaction caused by displacement reactions with the soil microbial biomass.     

Isolating the effect of soil properties on agricultural soil greenhouse gas emissions under controlled conditions

Agricultural soils are important sources of greenhouse gases (GHGs). Soil properties and environmental factors have complex interactions which influence the dynamics of these GHG fluxes. Four arable and five grassland soils which represent the range of soil textures and climatic conditions of the main agricultural areas in the UK were incubated at two different moisture contents (50 or 80% water holding capacity) and with or without inorganic fertiliser application (70 kg N ha⁻¹ ammonium nitrate) over 22 days. Emissions of N₂O, CO₂ and CH₄ were measured twice per week by headspace gas sampling, and cumulative fluxes were calculated. Multiple regression modelling was carried out to determine which factors (soil mineral N, organic carbon and total nitrogen contents, C:N ratios, clay contents and pH) that best explained the variation in GHG fluxes. Clay, mineral N and soil C contents were found to be the most important explanatory variables controlling GHG fluxes in this study. However, none of the measured variables explained a significant amount of variation in CO₂ fluxes from the arable soils. The results were generally consistent with previously published work. However, N₂O emissions from the two Scottish soils were substantially more sensitive to inorganic N fertiliser application at 80% water holding capacity than the other soils, with the N₂O emissions being up to 107 times higher than the other studied soils.     

不同氮水平下黄瓜-番茄日光温室栽培土壤N_2O排放特征

为探讨日光温室黄瓜—番茄种植体系内N2O排放动态变化及其对不同氮水平的响应规律,采用密闭静态箱法,研究了常规氮量(黄瓜季1 200 kg/hm2,番茄季900 kg/hm2)、比常规氮量减25%(黄瓜季900 kg/hm2,番茄季675 kg/hm2)、减50%(黄瓜季600 kg/hm2,番茄季450 kg/hm2)以及不施氮对日光温室土壤N2O排放的影响。结果表明,温度是影响日光温室土壤N2O排放强度的重要因素,4-10月(平均气温为27.4℃)的N2O排放通量最高达818.4μg/(m2·h);而2-3月(平均气温15.1℃)以及11-12月(平均气温14.7℃)期间的N2O排放通量最高仅为464.5μg/(m2·h),比4-10月的N2O排放峰值降低了43.2%。N2O排放峰值在氮肥追施后5 d内出现,N2O排放量集中在氮肥施用后7 d内,可占整个监测期(271 d)排放量的64.7%~67.8%。施氮因增加了土壤硝态氮含量而引起N2O排放爆发式增长,0~10 cm土壤硝态氮含量与N2O排放量呈指数函数关系(P0.01)。日光温室黄瓜—番茄种植体系内的N2O排放量为0.99~9.92 kg/hm2,其中75.6%~90.0%由施氮造成。与常规氮用量相比,氮减量25%和50%处理的N2O排放量分别降低了40.4%和59.3%,总产量却增加4.9%和7.4%。综上所述,合理减少氮用量不仅可显著降低日光温室土壤N2O排放,而且不会引起产量的降低。该研究为日光温室蔬菜生产构建科学合理的施氮技术及估算中国设施农田温室气体排放量提供参考。     

Evaluation of the fertilizer value and nutrient release from corn and soybean residues under laboratory and greenhouse conditions

Abstract

Laboratory and greenhouse studies were conducted on a moderately fertile Taloka (fine, mixed, thermic mollic Albaqualf) silt loam and a low fertility Leadvale (fine‐silty, siliceous, thermic typic Fragiudult) silt loam to evaluate nutrient release and fertilizer value of soybean [Glycine max (L.) Herr.] and corn (Zea mays L.) residues as compared to the inorganic fertilizer 13–13–13–13 (N‐P₂O₅‐K₂O‐S). Residues and the inorganic fertilizer were applied at 50 mg N/kg in a incubation study and at 25 and 50 mg N/kg in a greenhouse study. The incubation study indicted that carbon dioxide (CO₂) evolution and nitrogen (N) mineralization followed a identical sequence: soybean > corn residues, similar to residue N concentration and carbon/nitrogen (C/N) ratio sequence. Application of corn residues produced N immobilization in both soils (‐20 mg N/kg soil), whereas soybean increased inorganic soil N in the Leadvale soil (3 mg N/kg soil) and particularly in the Taloka soil (17 mg N/kg soil). The greenhouse study showed the superiority of the inorganic fertilizer over corn and soybean residues for sorghum‐sudan yield, and N, phosphorus (P), potassium (K), and sulfur (S) total uptake. No significant differences were found among the residues and between residues and the control with the exception of the higher soybean rate for total N uptake in the Taloka soil, and the higher corn and soybean residue rate in the Leadvale soil for total K uptake. It also appeared that soybean residues provided a substantial amount of N and S to sorghum‐sudan. Higher rates of both soybean and corn residues constituted a prime source of K, particularly in the Landvale soil which had a low exchangeable soil K level.     

Corn uptake of bromide under greenhouse and field conditions

Abstract

Bromide (Br) has been used frequently to trace the movement of fertilizer derived nitrate (NO₃) through the soil profile. Although not required for plant growth, Br is readily absorbed by plants. Consequently, the pulse of an anion tracer moving through the soil can be attenuated by actively growing plants. Greenhouse and field experiments were conducted to determine the amount of Br absorbed by corn, and to better understand potential competitive interactions between nitrogen (N) and Br in plant uptake. Under greenhouse conditions, over 85 percent of applied Brwas recovered by corn tops. Results from both greenhouse and field experiments demonstrated that the addition of Br or Cl neither reduced yield nor inhibited N uptake. Therefore, either Br or Cl could be used in N trials without concern for competitive inhibition of N uptake. However, both experiments demonstrated that N treatments affected Br concentration in the tissue, but this difference may have been due to increased yield of N treated plants causing Br dilution. Nitrogen treatments significantly affected plant Br uptake, but only in the greenhouse study. In the field experiment, corn recovery of 100 kg Br/ha applied in the spring of 1988 was as high as 38 percent in 1988, and 11 percent in 1989. This high rate of recovery demonstrates that the pulse of Br can be significantly reduced in the presence of developing plants, and should be taken into account when it is used as a tracer in leaching studies.     

Effect of straw biochar application on soil carbon,greenhouse gas emissions and nitrogen leaching: A vegetable crop rotation field experiment

Intensive vegetable crop systems are rapidly developing, with consequences for greenhouse gas (GHGs) emissions, nitrogen leaching and soil carbon. We undertook a field trial to explore the effect of biochar application (0, 10, 20 and 40 t ha⁻¹) on these factors in lettuce, water spinach and ice plant rotation. Our results show that the 20 and 40 t ha⁻¹ soil treatments resulted in the SOC content being 26.3% and 29.8% higher than the control (0 t ha⁻¹), respectively, with significant differences among all treatments (p < .05). Biochar application caused N₂O emissions to decrease during the lettuce and water spinach seasons, by 1.5%–33.6% and 12.4%–40.5%, respectively, compared the control, with the 20 t ha⁻¹ application rate resulting in the lowest N₂O emissions. Biochar also decreased the dissolved nitrogen (DN) concentration in leachate by 9.8%–36.2%, following a 7.3%–19.9% reduction in dissolved nitrogen in the soil. Similarly, biochar decreased the nitrate (NO₃⁻) concentrations in leachate by 3.9%–30.2%, following a 3.8%–16.7% reduction in the soil nitrate level. Overall, straw biochar applied at rate of 20 t ha⁻¹ produced the lowest N₂O emissions and N leaching, while, increasing soil carbon.     

Biochar amendment of chromium-polluted paddy soil suppresses greenhouse gas emissions and decreases chromium uptake by rice grain

Purpose

Soil chromium (Cr) pollution has received substantial attention owing to related food chain health risks and possible promotion of greenhouse gas (GHG) emissions. The aim of the present study was to develop a promising remediation technology to alleviate Cr bioavailability and decrease GHG emissions in Cr-polluted paddy soil.

Materials and methods

We investigated the potential role of biochar amendment in decreasing soil CO₂, CH₄, and N₂O emissions, as well in reducing Cr uptake by rice grains at application rates of 0 t ha^?1 (CK), 20 t ha^?1 (BC20), and 40 t ha^?1 (BC40) in Cr-polluted paddy soil in southeastern China. In addition, the soil aggregate size distribution, soil organic carbon (SOC) concentration of soil aggregates, soil available Cr concentration, and rice yield were analyzed after harvesting.

Results and discussion

Biochar amendment significantly reduced CO₂, CH₄, and N₂O emission fluxes. Compared to CK, total C emissions in the BC20 and BC40 treatments decreased by 9.94% and 17.13% for CO₂-C, by 30.46% and 37.10% for CH₄-C, and by 34.24% and 37.49% for N₂O-N, respectively. Biochar amendment increased the proportion of both the 2000–200 μm and 200–20 μm size fractions in the soil aggregate distribution. Accordingly, the organic carbon concentration of these fractions increased, which increased the total SOC. Moreover, biochar amendment significantly decreased soil available Cr concentration and total Cr content of the rice grains by 33.6% and 14.81% in BC20 and 48.1% and 33.33% in BC40, respectively. Rice yield did not differ significantly between biochar amendment treatment and that of CK.

Conclusions

Biochar application reduced GHG emissions in paddy soil, which was attributed to its comprehensive effect on the soil properties, soil microbial community, and soil aggregates, as well as on the mobility of Cr. Overall, the present study demonstrates that biochar has a great potential to enhance soil carbon sequestration while reducing Cr accumulation in rice grains from Cr-polluted rice paddies.

     

Slurry field management and ammonia emissions under Mediterranean conditions

In Spain, farmers are interested in applying pig (Sus scrofa domesticus) slurry (PS) to their fields throughout the year. During the spring and summer months, ammonia (NH₃) volatilization may be high. We studied the potential range of NH₃ losses under a warm and a hot period of the year, using available field practices, and two strategies: PS directly incorporated into the soil, in spring (I‐spring); and PS applied by splash‐plate, in summer time (SP‐summer), both to bare soil. Measurements were conducted, after PS application, using the micrometeorological mass balance integrated horizontal flux method. The cumulative NH₃‐N volatilization was 35% (I‐spring) and 60% (SP‐summer) of total ammonium nitrogen applied, and half of the total NH₃‐N losses happened by 17 h and 8 h, respectively, after application. Incorporation strategy was less effective in avoiding NH₃ losses than is described in the literature. This fact has important consequences for the implementation of NH₃ mitigation measures in Mediterranean agricultural systems.     

N mineralization and nitrate leaching from vegetable crop residues under field conditions: a model evaluation

Six different vegetable crop residues were incorporated in the field and N mineralization from the residues and from an unamended plot was followed over 4 months by periodically monitoring mineral N contents of the soil. The crop residues were also fractionated according to a modified Stevenson chemical fractionation. Nitrogen mineralization parameters of the first order kinetic model N(t)=N_A(1−e^−kt) were derived from the chemical fractionation data. The first order model was used in combination with a model describing the temperature dependence of N mineralization and a simple leaching model to predict N mineralization rates and nitrate redistribution after crop residue incorporation under field conditions. Comparison of predicted and measured mineral N contents in the upper soil layer (0–30 cm) before the start of leaching showed that the model was able to predict N mineralization from both soil organic matter and crop residues under field conditions. From the onset of leaching, mineral N contents were slightly overestimated in the upper layer and underestimated in the lower soil layers. Although the Burns leaching model underestimated the leaching rate, the general pattern of nitrate movement was simulated satisfactorily. Statistical analysis using the variance ratio test yielded small but significant F values, indicating that the model can still be improved. The modelling efficiency was rather high and the coefficient of residual mass very close to zero. Linear regression between measured and simulated nitrate contents over the whole profile (0–120 cm) for all samplings yielded Y=9.6+0.876X (r=0.94***) with all deviations smaller than 25 kg N ha⁻¹. Total N mineralization ranged from 48 kg N ha⁻¹ for the control plot to 136 kg N ha⁻¹ for the plots with cauliflower residues and cumulative leaching losses from 26–66 kg N ha⁻¹, with most of the mineral N left in the 60–120 cm layer. These results show that N losses by leaching in winter can be high when vegetable crop residues are incorporated, even when there is little mineral N in the soil at the time of incorporation.     

Tillage and crop straw methods affect energy use efficiency,economics and greenhouse gas emissions in rainfed winter wheat field of Loess Plateau in China

Data from a field experiment conducted in China's Loess Plateau (2013–2015) were used to determine the energy balance of winter wheat (Triticum aestivum L.) as affected by tillage and straw treatments. Tillage treatments included chisel plow, no tillage, and mouldboard plow. Crop straw levels included straw returning and straw removed. The energy balance was evaluated by comparing the following parameters: net energy, energy profitability, energy use efficiency, and energy intensity. The yield parameters were significantly influenced by the tillage treatments and revealed that the chisel plow entailed fewer field operations and lower energy requirements with a higher yield than mouldboard plowing tillage. The highest proportion of energy input came from a nitrogen fertiliser, followed by diesel fuel. The total energy input applied per hectare increased with an increase in the tillage intensity, and the lowest energy input was required for the no tillage case with the straw returning treatment, and the highest for the case of mouldboard plow with the straw returning treatment. The lowest average energy intensity was recorded for the no tillage case, followed by the case of chisel plow tillage in both cropping seasons. Moreover, in the case of mouldboard plough tillage, the maximum energy intensity was recorded in both cropping seasons. In the cases of the chisel plow tillage and the no tillage, we observed the maximum energy gain, while in the no tillage case, we observed the maximum energy use efficiency. The net return and the benefit/cost ratio were higher in the case of straw returning than those in the case of no straw treatment. We concluded that no tillage and chisel plow tillage with straw returning could improve the energy use efficiency and the benefit/cost ratio of winter wheat production systems.     

麦秸与毛叶苕子共同调控青海高原土壤温室气体排放的作用机制

  【目的】  研究青海高原麦秸和豆科绿肥混合添加下土壤温室气体排放规律及其碳氮转化机制,为该地区农田系统秸秆和绿肥科学利用提供依据。  【方法】  采用室内模拟试验,设无添加对照(CK)、单独添加毛叶苕子(VS)、单独添加麦秸(WS)、麦秸与毛叶苕子混合添加(VWS),共4个处理。测定了温室气体排放速率、土壤活性碳氮组分、土壤酶活性、细菌、古菌、真菌、amoA、nirK和narG基因丰度。  【结果】  VWS处理与VS处理相比,CO₂和N₂O的累积排放量分别减少24.8%和74.6%,CH₄累积吸收量增加9.1%,综合增温潜势(global warming potential, GWP)显著降低76.1% (P<0.05);与WS处理相比,CO₂累积排放量增加33.7%,CH₄累积吸收量与N₂O累积排放量分别降低12.0%和43.1%,GWP降低49.4%。有机物料添加可调节土壤pH,增加土壤碳氮含量。VWS处理的土壤pH显著高于CK和VS处理;土壤水溶性有机碳(DOC)和微生物量碳(SMBC)含量较VS处理分别增加了21.6%和4.9%,无机氮(Nmin)、土壤水溶性有机氮(DON)和微生物量氮(SMBN)含量分别降低了77.3%、59.5%和6.3%;土壤Nmin、DOC、DON、SMBC和SMBN含量较WS处理分别增加64.0%、22.5%、56.5%、23.2%和27.8%。VWS处理较其他处理,α-葡萄糖苷酶(AG)和β-葡萄糖苷酶(BG)活性显著提高,亚硝酸还原酶(NIR)活性显著降低。VWS处理的真菌和古菌群落丰度较WS处理分别提高83.8%和69.8%,较VS处理分别降低62.6%和20.3%;VWS处理细菌群落丰度较VS处理降低33.4%。VWS处理下,AOB amoA、nirK和narG基因丰度较VS处理分别降低56.6%、41.4%和16.3%,较WS处理分别降低30.3%、25.9%和12.0%。相关分析结果表明,CO₂和CH₄排放与土壤有机碳、全氮、DOC、SMBC和SMBN含量,AG、NAG和NR活性,真菌、细菌、nirK和narG基因丰度呈显著正相关;N₂O排放与土壤全氮、DON、SMBC和SMBN含量、真菌、AOB amoA和nirK基因丰度呈显著正相关,与土壤pH和BG活性呈显著负相关。偏最小二乘路径模型分析(PLS-PM)表明,AOB amoA是调控土壤N₂O排放的主要功能菌群。  【结论】  麦秸、毛叶苕子单独添加以及二者混合添加均可促进土壤CO₂排放,减少CH₄吸收。相较于二者单独添加,混合添加可通过降低土壤AOB群落丰度等途径,实现N₂O减排和综合增温潜势下降,可作为青海高原旱地土壤温室气体减排的一项有效措施。     

Contrasting effects of wheat straw and its biochar on greenhouse gas emissions and enzyme activities in a Chernozemic soil

Biochar produced from plant biomass through pyrolysis has been shown to be much more resistant to biodegradation in the soil as compared with the raw biomass, such as cereal straw that is routinely shredded and discharged on to farm fields in large amounts. Biochar application to soil has also been reported to decrease greenhouse gas (GHG) emissions, although the mechanisms are not fully understood. In this study, the emissions of three main GHGs (CO₂, CH₄, and N₂O) and enzyme activities (urease, β-glycosidase, and dehydrogenase) were measured during a 100-day laboratory incubation of a Chernozemic soil amended with either straw or its biochar at rates of 0.67 and 1.68 % (based on the amount of C added) for the low and high rates, respectively. The biochar application dramatically reduced N₂O emissions, but CO₂ or CH₄ emissions were not different, as compared with the un-amended soil. At the same C equivalent application rate, CO₂ and N₂O emission rates were greater while CH₄ emission rates were lower in straw than in biochar application treatments. The activities of both the dehydrogenase and β-glycosidase significantly declined while that of urease significantly increased with the biochar as compared with the straw treatment. We conclude that pyrolysis of cereal straw prior to land application would significantly reduce CO₂ and N₂O emissions, in association with changed enzyme activities, while increasing the soil C pool through the addition of stable C in the form of biochar.     

Occurrence and distribution study of residues from pesticides applied under controlled conditions in the field during rice processing

The results of an experiment to study the occurrence and distribution of pesticide residues during rice cropping and processing are reported. Four herbicides, nine fungicides, and two insecticides (azoxystrobin, byspiribac-sodium, carbendazim, clomazone, difenoconazole, epoxiconazole, isoprothiolane, kresoxim-methyl, propanil, quinclorac, tebuconazole, thiamethoxam, tricyclazole, trifloxystrobin, λ-cyhalotrin) were applied to an isolated rice-crop plot under controlled conditions, during the 2009-2010 cropping season in Uruguay. Paddy rice was harvested and industrially processed to brown rice, white rice, and rice bran, which were analyzed for pesticide residues using the original QuEChERS methodology and its citrate variation by LC-MS/MS and GC-MS. The distribution of pesticide residues was uneven among the different matrices. Ten different pesticide residues were found in paddy rice, seven in brown rice, and eight in rice bran. The highest concentrations were detected in paddy rice. These results provide information regarding the fate of pesticides in the rice food chain and its safety for consumers.     

Potential short-term effects of yak and Tibetan sheep dung on greenhouse gas emissions in two alpine grassland soils under laboratory conditions

Yak and Tibetan sheep graze extensively on natural grasslands in the Qinghai-Tibetan Plateau, and large amounts of excrement are directly deposited onto alpine grasslands. However, information on greenhouse gas (GHG) emissions from this excrement is limited. This study evaluated the short-term effects of yak and Tibetan sheep dung on nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) emissions from alpine steppe soil at a water holding capacity (WHC) of 40 or 60 % and from alpine meadow soil at a WHC of 60 or 80 % under laboratory conditions. Cumulative N₂O emissions over a 15-day incubation period at low soil moisture conditions ranged from 111 to 232 μg N₂O–N kg soil^?1 in the yak dung treatments, significantly (P?<?0.01) higher than that of sheep dung treatments (28.7 to 33.7 μg N₂O–N kg soil^?1) and untreated soils (1.04–6.94 μg N₂O–N kg soil^?1). At high soil moisture conditions, N₂O emissions were higher from sheep dung than yak dung and non-treated soils. No significant difference was found between the yak dung and non-treated alpine meadow soil at 80 % WHC. Low N₂O emission in the yak dung treatment from relatively wet soil was probably due to complete denitrification to N₂. Yak dung markedly (P?<?0.001) increased CH₄ and CO₂ emissions, likely being the main source of these two gases. The addition of sheep dung markedly (P?<?0.001) elevated CO₂ emissions. Dung application significantly (P?<?0.01) increased global warming potential, particularly for alpine steppe soil. In conclusion, our findings suggest that yak and Tibetan sheep dung deposited on alpine grassland soils may increase GHG emissions.     

Responses of methane emissions and rice yield to applications of biochar and straw in a paddy field

Purpose

Directly returning straw back to the paddy field would significantly accelerate methane (CH₄) emission, although it may conserve and sustain soil productivity. The application of biochar (biomass-derived charcoal) in soil has been proposed as a sustainable technology to reduce methane (CH₄) emission and increase crop yield. We compared the effects of either biochar or rice straw addition with a paddy field on CH₄ emission and rice yield.

Materials and methods

A 2-year field experiment was conducted to investigate a single application of rice straw biochar (SC) and bamboo biochar (BC) (at 22.5 t ha^?1) in paddy soil on CH₄ emission and rice yield as compared with the successive application (6 t ha^?1) of rice straw (RS). Soil chemical properties and methanogenic and CH₄ oxidation activities in response to the amendment of biochar and rice straw were monitored to explain possible mechanism.

Results and discussion

SC was more efficient in reducing CH₄ emission from paddy field than BC. Incorporating SC into paddy field could decrease CH₄ emission during the rice growing cycle by 47.30 %–86.43 % compared with direct return of RS. This was well supported by the significant decrease of methanogenic activity in paddy field with SC. In comparison to a non-significant increase with BC or RS application, rice yield was significantly raised with SC amendment by 13.5 % in 2010 and 6.1 % in 2011. An enhancement of available K and P and an improvement in soil properties with SC amendment might be the main contributors to the increased crop yield.

Conclusions

These results indicated that conversion of RS into biochar instead of directly returning it to the paddy field would be a promising method to reduce CH₄ emission and increase rice yield.