减氮配施稻秆生物炭对稻田土壤养分及植株氮素吸收的影响

通过2018年早稻和晚稻田间试验,研究化学氮肥减量及配施稻秆生物炭对稻田土壤养分特性及植株氮素吸收的影响。试验包括6个处理:不施氮(CK)、常规施氮(N₁₀₀)、减氮20%(N₈₀)、减氮20%配施生物炭(N₈₀+BC)、减氮40%(N₆₀)、减氮40%配施生物炭(N₆₀+BC)。结果表明: 与常规施氮相比,单纯减氮20%和40%或配施生物炭对早晚稻不同生育期土壤pH、有机质、全氮、铵态氮、全磷、有效磷、全钾、速效钾无显著影响;减氮20%配施生物炭显著增加晚稻分蘖期的土壤阳离子交换量(CEC),而减氮40%配施生物炭则显著增加晚稻抽穗期的电导率(EC)值。与单纯减氮相比,N₈₀+BC的土壤速效钾含量在早晚稻抽穗期均显著升高,土壤pH值、全氮在晚稻成熟期显著增加;N₆₀+BC的土壤全钾含量在早稻成熟期显著升高。不同处理早稻土壤硝态氮含量随生育进程逐渐降低,与分蘖期相比,抽穗期和成熟期的常规施氮土壤硝态氮含量分别降低50.0%和71.6%,而配施生物炭处理则降低6.3%～45.5%,减氮配施生物炭显著降低了硝态氮的流失。在晚稻抽穗期,减氮配施生物炭植株吸氮量显著高于常规施氮和单纯减氮,增加幅度为34.8%～52.4%。综上,适度的减氮或配施稻秆生物炭能有效保持土壤养分,促进水稻对氮素的吸收,提高氮素利用率。     

生物炭配施硝化/脲酶抑制剂对亚热带水稻土活性氮气体排放的影响

探究施用生物炭和脲酶抑制剂/硝化抑制剂对亚热带水稻土氮素硝化过程的调控作用、氨挥发和N₂O排放的温室效应潜能的影响,确定生物炭与硝化和脲酶抑制剂的最佳组合,可为削减施用氮肥带来的活性氮气体排放对环境的负面风险提供理论依据。本研究采用室内好气培养试验方式,以单施尿素(N)为对照,设置7个试验处理[尿素+生物炭(NB),尿素+硝化抑制剂(N+NI),尿素+脲酶抑制剂(N+UI),尿素+硝化抑制剂+脲酶抑制剂(N+NIUI),尿素+硝化抑制剂+生物炭(NB+NI),尿素+脲酶抑制剂+生物炭(NB+UI),尿素+硝化抑制剂+脲酶抑制剂+生物炭(NB+NIUI)],观测生物炭与脲酶抑制剂(NBPT)/硝化抑制剂(DMPP)配施下土壤无机氮含量、N₂O排放及氨挥发的变化动态。结果表明: 1)培养期间,与N处理(5.11 mg N·kg^-1·d^-1)相比,NB处理的土壤硝化速率常数显著增加33.9%,N+NI处理显著降低22.9%;NB处理显著提高了氨氧化细菌(AOB)丰度,增幅达56.0%。2)与N处理相比,N+NI和NB+NI处理的NH₃累积排放量均显著增加约49%;N+UI处理降低了NH₃累积损失量,NB+UI处理抑制效果更明显。3)各处理的N₂O排放速率高峰均出现在施肥后前10 d;NB处理的N₂O排放高峰出现最早,N处理排放速率最高(5.87 μg·kg^-1·h^-1);硝化抑制剂与脲酶抑制剂配施减少土壤N₂O排放的效果最佳。综合计算各处理直接N₂O和间接N₂O(NH₃)排放产生的温室效应潜能(GWP)发现,N+NI和NB+NI处理较N处理分别增加了34.8%和40.9%,而NB和NB+UI处理的GWP显著降低了45.9%和60.5%。因此,生物炭与脲酶抑制剂配施对降低土壤活性氮气体排放所产生的温室效应潜能效果最佳。     

不同施肥处理对土壤活性有机碳和甲烷排放的影响

通过采集田间试验区连续3a施入有机肥的稻田耕层土壤,分析土壤中微生物量碳(MBC)、水溶性有机碳(DOC)、易氧化有机碳(ROC)和可矿化有机碳(readily mineralizable carbon,RMC)等活性有机碳的含量,稻田甲烷(CH_4)的排放通量,探讨施用有机肥的土壤活性有机碳变化及与CH_4排放的关系。研究结果显示:(1)施有机肥对土壤中的活性有机碳均有一定的促进作用。3a不同施肥处理土壤中DOC、ROC、MBC和RMC的平均含量分别为383.6、2501.2、640.4 mg/kg和291.7 mg/kg。3a施猪粪(猪粪+化肥,PM)、鸡粪(鸡粪+化肥,CM)和稻草(稻草+化肥,RS)的DOC的含量分别比化肥(CF)处理增加5.6%、6.7%和19.3%,ROC的含量分别比CF增加6.6%、8.4%和9.8%;MBC含量分别比CF增加5.1%、14.8%和21.5%,RMC增加6.8%、22.0%和33.9%。不同施肥处理的稻田土壤活性有机碳为分蘖期高于成熟期。(2)施肥处理显著增加稻田CH_4排放,CH_4分蘖期的排放通量是成熟期的143倍,3a PM、CM和RS处理的CH_4排放分别比CF处理增加37.0%(P0.05)、92.7%(P0.05)和99.4%(P0.05)。(3)不同施肥处理的DOC、ROC、MBC和RMC含量与CH_4排放通量均存在显著正相关关系,ROC与CH_4排放的相关系数最高,为0.754(P0.01),且4种有机碳间关系密切。稻田分蘖期土壤中的活性有机碳与稻田CH_4排放呈显著正相关关系。(4)综合分析,在4种有机碳中,土壤中ROC和MBC的含量直接影响CH_4排放。     

生物炭添加对土壤呼吸和有机碳含量的影响

以菜地和果园土壤为研究对象,通过室内培养实验,向土壤中分别添加不同材料制备的生物炭(马尼拉草、阔叶和竹叶),热解温度为350℃,研究不同材料制备生物炭添加对土壤呼吸和有机碳含量的影响.结果表明：不同生物炭施入土壤后,土壤 CO 2释放速率总的趋势是前期分解速率快,后期缓慢.在整个培养过程中(28 d),随着培养时间的延长,土壤 CO 2释放速率下降趋势逐渐降低.在不同土壤培养条件下,均是添加阔叶生物炭后土壤 CO 2-C 累计释放增多,果园和菜地土壤 CO 2-C 累计分别达到482．57和424．72 mg·kg-1.添加不同的生物炭均能提高土壤有机碳含量,但只有添加阔叶生物炭之后,差异才会达到显著(P ＜0．05).研究结果为正确利用生物炭和评价其在土壤碳库作用提供科学依据.     

Effects of tillage and nitrogen fertilizers on CH4 and CO2 emissions and soil organic carbon in paddy fields of central China

Quantifying carbon (C) sequestration in paddy soils is necessary to help better understand the effect of agricultural practices on the C cycle. The objective of the present study was to assess the effects of tillage practices [conventional tillage (CT) and no-tillage (NT)] and the application of nitrogen (N) fertilizer (0 and 210 kg N ha(-1)) on fluxes of CH(4) and CO(2), and soil organic C (SOC) sequestration during the 2009 and 2010 rice growing seasons in central China. Application of N fertilizer significantly increased CH(4) emissions by 13%-66% and SOC by 21%-94% irrespective of soil sampling depths, but had no effect on CO(2) emissions in either year. Tillage significantly affected CH(4) and CO(2) emissions, where NT significantly decreased CH(4) emissions by 10%-36% but increased CO(2) emissions by 22%-40% in both years. The effects of tillage on the SOC varied with the depth of soil sampling. NT significantly increased the SOC by 7%-48% in the 0-5 cm layer compared with CT. However, there was no significant difference in the SOC between NT and CT across the entire 0-20 cm layer. Hence, our results suggest that the potential of SOC sequestration in NT paddy fields may be overestimated in central China if only surface soil samples are considered.     

炉渣与生物炭施加对稻田土壤碳库及微生物的影响

以福州平原稻田为实验区,在2015年早、晚稻秧苗移栽前,对稻田进行施加生物炭、炉渣、生物炭+炉渣（混施）处理,并以不施加处理作为对照。为了了解施加处理的后续效应,于2017年检测早、晚稻拔节期和成熟期土壤有机碳含量及真菌、细菌数量。结果表明：3种施加处理稻田土壤有机碳（SOC）含量均比对照组有显著提高（P < 0.05）,但溶解性有机碳（DOC）、易氧化碳（EOC）、土壤微生物量碳（MBC）含量各处理之间差异不显著（P > 0.05）。与对照组相比,各施加处理组在一定程度上提高了土壤中真菌和细菌数量,但差异不显著（P > 0.05）。细菌数量与DOC含量呈极显著负相关（P < 0.01）,与EOC含量呈显著负相关（P < 0.05）,与MBC含量呈显著正相关（P < 0.05）。真菌/细菌比值与真菌数量、DOC含量呈极显著正相关（P < 0.01）。说明炉渣和生物炭施加处理2年后,仍可提高稻田土壤的碳库稳定性,并增加土壤微生物数量。     

生物炭施用的固碳减排潜力及农田效应

气候变暖及粮食安全是保证人类可持续发展的重要课题。生物炭具有较高的稳定性、较高碳含量等特点,能增加土壤碳储量,提高土壤物理及化学性质,提高农田产出,能应对高温胁迫及土壤退化双重压力,具有一举多赢的生态环境效益,在缓解温室效应及粮食危机方面展现出巨大的潜力。综合前人研究成果,分析了生物炭固碳减排潜力及农田效应影响因素(包括:生物炭原料、制备温度、施用量、土壤类型等)。综合固碳减排及提高产出两方面因素,提出了较合适的生物炭施用标准,即300—700℃制备的农林废弃物生物炭,且施用量不超过5%。对生物炭固碳减排及田间效应领域未来的研究方向进行了展望。     

溶解性有机碳在红壤水稻土中的吸附及其影响因素

吸附作用是影响土壤中溶解性有机碳(DOC)迁移转化及生物有效性的重要反应过程,研究DOC在土壤中的吸附行为,对正确阐明土壤有机碳的循环和转化特征以及进行污染风险评估有重要意义.采用平衡法研究了红壤水稻土对DOC的吸附特征,并分析土壤有机质、粘粒含量及pH值与DOC吸附量之间的关系.结果表明,供试土壤对DOC的吸附等温线符合Freundlich和Linear方程.不同土壤对DOC的吸附能力有明显差异.在相同浓度下,DOC吸附量以第四纪红色粘土发育的低肥力水稻土最大,第三纪红砂岩风化物发育的低肥力水稻土次之,两种高肥力水稻土最小.土壤对DOC的吸附过程分为快、慢两个阶段,0-0.25 h内DOC的吸附速率最大,随着时间的推移,吸附速率渐小,2-4 h后基本达到吸附平衡.描述供试土壤对DOC吸附动力学过程的最优模型为一级扩散方程,其次为Elovich方程和抛物扩散方程.粘粒含量和有机质是影响土壤DOC吸附量的重要因素,随着粘粒含量的增加,有机质含量的降低,DOC的吸附量增大.     

施肥对红壤水稻土团聚体分布及其碳氮含量的影响

依托中国科学院千烟洲生态试验站,利用1998年建立的红壤水稻田长期定位施肥试验,研究秸秆还田(ST)、化肥(NPK)、有机肥(OM)等施肥方式对红壤水稻土各粒级团聚体分布及其碳氮含量影响。结果表明:在所有施肥处理条件下红壤水稻土团聚体分布以<63μm的粉砂和粘粒为主,占41%—54%,长期施肥特别是施用OM有利于促进红壤水稻土大粒级团聚体形成;分别施用ST、NPK和OM均能提高红壤水稻土全土及各粒级团聚体中的有机碳和全氮含量,施用OM提高幅度最大。因此,在我国南方红壤稻作区的农业生产过程中应施用有机肥,从而改善土壤结构、碳贮量和养分状况。     

Measuring carbon dynamics in field soils using soil spectral reflectance: prediction of maize root density, soil organic carbon and nitrogen content

This paper reports the development of a proximal sensing technique used to predict maize root density, soil carbon (C) and nitrogen (N) content from the visible and near-infrared (Vis-NIR) spectral reflectance of soil cores. Eighteen soil cores (0?C60?cm depth with a 4.6?cm diameter) were collected from two sites within a field of 90-day-old maize silage; Kairanga silt loam and Kairanga fine sandy loam (Gley Soils). At each site, three replicate soil cores were taken at 0, 15 and 30?cm distance from the row of maize plants (rows were 60?cm apart). Each soil core was sectioned at 5 depths (7.5, 15, 30, 45, and 60?cm) and soil reflectance spectra were acquired from the freshly cut surface at each depth. A 1.5?cm soil slice was taken at each surface to obtain root mass and total soil C and N reference (measured) data. Root densities decreased with depth and distance from plant and were lower in the silt loam, which had the higher total C and N contents. Calibration models, developed using partial least squares regression (PLSR) between the first derivative of soil reflectance and the reference data, were able to predict with moderate accuracy the soil profile root density (r ²?=?0.75; ratio of prediction to deviation [RPD]?=?2.03; root mean square error of cross-validation [RMSECV]?=?1.68?mg/cm³), soil% C (r ²?=?0.86; RPD?=?2.66; RMSECV?=?0.48%) and soil% N (r ²?=?0.81; RPD?=?2.32; RMSECV?=?0.05%) distribution patterns. The important wavelengths chosen by the PLSR model to predict root density were different to those chosen to predict soil C or N. In addition, predicted root densities were not strongly autocorrelated to soil C (r?=?0.60) or N (r?=?0.53) values, indicating that root density can be predicted independently from soil C. This research has identified a potential method for assessing root densities in field soils enabling study of their role in soil organic matter synthesis.     

Long-term tillage effects on soil organic carbon and dissolved organic carbon in a purple paddy soil of Southwest China

The impact of conservation tillage practices on soil carbon has been of great interest in recent years. Conservation tillage might have the potential to enhance soil carbon accumulation and alter the depth distribution of soil carbon compared to conventional tillage based systems. Changes in the soil organic carbon (SOC) as influenced by tillage, are more noticeable under long-term rather than short-term tillage practices. The objective of this study was to determine the impacts of long-term tillage on SOC and dissolved organic carbon (DOC) status after 19 years of four tillage treatments in a Hydragric Anthrosol. In this experiment four tillage systems included conventional tillage with rotation of rice and winter fallow system (CTF), conventional tillage with rotation of rice and rape system (CTR), no-till and ridge culture with rotation of rice and rape system (NT) and tillage and ridge culture with rotation of rice and rape system (TR). Soils were sampled in the spring of 2009 and sectioned into 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm depth, respectively.Tillage effect on SOC was observed, and SOC concentrations were much larger under NT than the other three tillage methods in all soil depths from 0 to 60 cm. The mean SOC concentration at 0–60 cm soil depth followed the sequence: NT (22.74 g kg^?1) > CTF (14.57 g kg^?1) > TR (13.10 g kg^?1) > CTR (11.92 g kg^?1). SOC concentrations under NT were significantly higher than TR and CTR (P < 0.01), and higher than CTF treatment (P < 0.05). The SOC storage was calculated on equivalent soil mass basis. Results showed that the highest SOC storage at 0–60 cm depth presented in NT, which was 158.52 Mg C ha^?1, followed by CTF (106.74 Mg C ha^?1), TR (93.11 Mg C ha^?1) and CTR (88.60 Mg C ha^?1). Compared with conventional tillage (CTF), the total SOC storage in NT increased by 48.51%, but decreased by 16.99% and 12.77% under CTR and TR treatments, respectively. The effect of tillage on DOC was significant at 0–10 cm soil layer, and DOC concentration was much higher under CTF than the other three treatments (P < 0.01). Throughout 0–60 cm soil depth, DOC concentrations were 32.92, 32.63, 26.79 and 22.10 mg kg^?1 under NT, CTF, CTR and TR, and the differences among the four treatments were not significant (P > 0.05). In conclusion, NT increased SOC concentration and storage compared to conventional tillage operation but not for DOC.     

Ozone pollution influences soil carbon and nitrogen sequestration and aggregate composition in paddy soils

Background and aims

Much attention has focused on the effects of tropospheric ozone (O₃) on terrestrial ecosystems and plant growth. Since O₃ pollution is currently an issue in China and many parts of the world, understanding the effects of elevated O₃ on soil carbon (C) and nitrogen (N) sequestration is essential for efforts to predict C and N cycles in terrestrial ecosystems under predicted increases in O₃. Thus the main objective of this study was to determine whether an increases in atmospheric O₃ concentration influenced soil organic C (SOC) and N sequestration.

Methods

A free-air O₃ enrichment (O₃-FACE) experiment was started in 2007 and used continuous O₃ exposure from March to November each year during crop growth stage in a rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation field in the Jiangsu Province, China. We investigated differences in SOC and N and soil aggregate composition in both elevated and ambient O₃ conditions.

Results

Elevated atmospheric O₃ (18–80 nmol mol^?1 or 50 % above the ambient) decreased the SOC and N concentration in the 0–20 cm soil layer after 5 years. Elevated O₃ significantly decreased the SOC concentration by 17 % and 5.6 % in the 0–3 cm and the 10–20 cm layers, respectively. Elevated O₃ significantly decreased the N concentration by 8.2–27.8 % in three layers at the 20 cm depth. In addition, elevated O₃ influenced the formation and transformation of soil aggregates and the distribution of SOC and N in the aggregates across soil layer classes. Elevated O₃ significantly decreased the macro-sized aggregate fraction (16.8 %) and associated C and N (0.5 g kg^?1 and 0.32 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (61 %) and associated C (1.7 g kg^?1) in the 0–3 cm layer. Elevated O₃ significantly decreased the macro-sized aggregate fraction (9.6 %) and associated C and N (1.4 g kg^?1 and 0.35 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (41.8 %) and decreased the corresponding associated N (0.14 g kg^?1) in the 3–10 cm layer. Elevated O₃ did not significantly effect the formation and transformation of aggregates in the 10–20 cm layer, yet it did significantly increase the C concentration in the macro-sized fraction (1 g kg^?1) and decrease the N concentration in the macro- and micro-sized fractions (0.24 g kg^?1 and 0.16 g kg^?1, respectively).

Conclusion

Long-term exposure to elevated atmospheric O₃ negatively affected the physical structure of the soil and impaired soil C and N sequestration.     

氮肥减量配施生物炭对黄壤稻田土壤有机碳活性组分和矿化的影响

化肥减施增效有助于农业的可持续发展。本研究用等氮量生物炭替代化肥氮,设置0、10%、20%、30%、40%(CK,T₁～T₄) 5个替代比例,在水稻收获后采集土壤样品进行室内分析,研究氮肥减量配施生物炭对黄壤稻田土壤有机碳活性组分和矿化的影响。结果表明: 氮肥减量配施生物炭均可显著提高土壤有机碳(SOC)含量,且与生物炭配施量呈正比。氮肥减施20%条件下,土壤微生物生物量碳(MBC)和易氧化碳(ROC)含量均最高,分别为293.68和250.00 mg·kg^-1,土壤可溶性碳(DOC)含量最低。SOC矿化速率在培养的第3天达到最高,前期(第3~6天)迅速下降,中期(第6~18天)缓慢下降,后期(第18~30天)趋于稳定,矿化速率随时间的动态变化符合对数函数;SOC累积矿化量和累积矿化率分别为0.66～0.86 g·kg^-1和2.9%～4.0%,均以T₂处理最低。稻谷产量随氮肥减施比例的增加呈先增加后下降趋势,T₂处理最高,比CK显著增加了13.4%。本试验条件下,化学氮肥减量20%配施适量生物炭(5 t·hm^-2)可有效提高SOC、MBC、ROC含量和水稻产量,降低SOC累积矿化量和累积矿化率,增强土壤固碳能力,是贵州黄壤稻田土壤固碳培肥的较好选择。     

不同类型农田土壤对可溶性有机氮、碳的吸附特性

研究了陕西关中地区红油土和淋溶褐土耕层土壤对分离的有机肥提取液中可溶性有机氮、碳(SON和SOC)的吸附特性.结果表明:原始物质吸附等温线方程可以反映土壤对可溶性有机氮、碳的吸附特性,土壤吸附SON、SOC的数量与它们各自加入的量呈极显著线性关系.从原始物质吸附等温线方程的分配系数m看,淋溶褐土对SON、SOC的吸附能力强于红油土.红油土对SON、SOC的平均吸附率分别为24.3%和18.8%,淋溶褐土则分别为38.3%和18.6%;两种类型土壤对SON和SOC的吸附能力较低,说明它们在土壤中具有较强的移动性;土壤对SOC的吸附能力弱于SON,说明SOC更易于从土壤中流失.     

双季稻田冬季种植模式对土壤有机碳和碳库管理指数的影响

为探讨冬季覆盖作物还田对稻田土壤碳库的影响,通过冬季种植油菜、紫云英、黑麦草、马铃薯,并以冬闲为对照进行大田试验,测定了不同冬季作物模式下早稻和晚稻的土壤有机碳、活性有机碳含量,并计算了稳态碳、碳库活度、活度指数、碳库指数和土壤碳库管理指数.结果表明:冬季作物还田增加了土壤有机碳含量,早稻和晚稻后的土壤有机碳含量比对照分别提高了1%～8%和3%～18%;油菜、黑麦草和紫云英还田均促进了土壤活性有机碳含量的增加,早稻后增加16.2%～84.2%,晚稻后增加24.4%～28.1%;冬季作物还田增加了土壤碳库管理指数,增加幅度为1.4%～41.8%.综上所述,冬种作物还田有利于提高土壤的固碳效应,并提升土壤质量,以种植黑麦草、紫云英的综合效果较佳.     

生物质炭对水稻土团聚体微生物多样性的影响

生物质炭施用对土壤微生物群落结构的影响已有报道,但土壤团聚体粒组中微生物群落对生物质炭施用的响应的研究还相对不足。以施用玉米秸秆生物质炭两年后的水稻土为对象,采用团聚体湿筛法,通过高通量测序对土壤团聚体的微生物群落结构与多样性进行分析,结果表明:(1)与对照相比,生物质炭施用显著促进了大团聚体(2000—250μm)的形成,并提高了团聚体的稳定性。(2)不同粒径团聚体间微生物相对丰度存在显著差异。在未施生物质炭的处理(C0)中,随着团聚体粒径增大,变形菌门、子囊菌门、β-变形杆菌目、格孢腔菌目的相对丰度逐渐降低,而酸杆菌门、担子菌门、粘球菌目、类球囊霉目的相对丰度逐渐升高。(3)生物质炭施用显著改变了团聚体间的微生物群落结构。与C0处理相比,生物质炭施用处理的大团聚体中变形菌门、鞭毛菌门和β-变形杆菌目的相对丰度分别显著提高了14.37%、33.28%和33.82%;微团聚体(250—53μm)中酸杆菌门、子囊菌门和粘球菌目的相对丰度分别显著降低了20.15%、19.93%和17.66%;粉、黏粒组分(<53μm)中担子菌门的相对丰度升高90.25%,而子囊菌门和鞭毛菌门的相对丰...     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Effect of infiltration rate on nitrogen dynamics in paddy soil after high-load nitrogen application containing N tracer

Flooded paddy fields perform many ecological and conservation functions and are also reported to facilitate livestock waste disposal. Paddy field infiltration rates are important for nitrogen dynamics. A laboratory study was conducted to compare the effects of infiltration rate on nitrogen dynamics including nitrogen leaching, soil adsorption, microorganism assimilation, plant uptake and denitrification. Two infiltration rates were applied to paddy soil: 18.6 ± 10.3 mm d⁻¹ (High Infiltration Columns: HIC) and 4.49 ± 3.15 mm d⁻¹ (Low Infiltration Columns: LIC). Total nitrogen load was 484 kg-N ha⁻¹, with the ammonium ion form including basal fertilizer and a double supplemental fertilizer application. A (¹⁵NH₄)₂SO₄ tracer was applied in each infiltration rate as supplemental fertilizer.Nitrification and denitrification, plant uptake, soil adsorption, and leaching differed between infiltration rates. Compared with high nitrate concentration in HIC soil water, little nitrate appeared in the LIC, and it maintained relatively higher soil water ammonium concentrations long after application. The ¹⁵N assimilated by rice and contained in the LIC soil was higher than in the HIC, suggesting that low infiltration is beneficial to nitrogen assimilation, adsorption and fixation. Although loss of nitrogen via leaching was higher in the HIC than the LIC, it accounted for only 3.94% of total ¹⁵N input. About 69.4% of total ¹⁵N input was unaccounted for in the HIC, whereas 38.3% of total ¹⁵N input was unaccounted for in the LIC. According to the denitrification rate calculated from changes in ²⁹N₂/²⁸N₂ and ³⁰N₂/²⁸N₂ ratios, the denitrification rate after HIC application was higher than the LIC, reaching a maximum rate of 2.9 g m⁻² d⁻¹. This suggests that high infiltration rate enhances nitrification and denitrification, with most of the unaccounted inputted ¹⁵N in the HIC was probably lost through nitrification and denitrification.     

不同稻作模式下稻田土壤活性有机碳变化动态

通过大田试验,研究了稻鸭复合种养(RD)、间歇灌溉(RW)、常规淹水灌溉(CK)3种不同稻作模式下稻田土壤可溶性有机碳(DOC)、易氧化态有机碳(ROC)和微生物生物量碳(MBC)3种活性有机碳组分的动态变化规律.结果表明:3种稻作模式下土壤DOC、MBC在水稻拔节-齐穗阶段含量最高;ROC在水稻整个生育期内变化平稳,没有表现出显著的阶段性差异.MBC受水稻生育期的影响最大;DOC受水稻生育期和稻作模式的影响均较大;而ROC主要受稻作模式的影响.与CK相比,RD能显著提高土壤DOC和ROC及其有效率;而RW极显著降低了DOC及其有效率,明显提高了ROC及其有效率.3处理间MBC及微生物熵均没有显著差异.     

土壤有机碳对外源氮添加的响应及其机制

土壤有机碳库是陆地生态系统碳库的重要组成, 在全球碳循环中发挥着重要的作用。受元素化学计量平衡调控作用, 氮输入的增加将会对土壤有机碳库产生重要影响。然而, 目前关于陆地生态系统碳库对氮添加的响应主要集中在植被碳库, 对土壤碳库研究较少, 且研究结论争议较大, 尤其对其响应机制缺少系统梳理。该文作者通过对已有文献进行梳理, 认为生态系统类型、土壤碳变化的检测方法、土壤深度, 以及土壤稳定性碳和易变碳含量的差异可能是造成当前研究土壤碳汇增量(每克氮输入所增加的碳)差异的重要原因。氮添加条件下土壤有机碳的积累机制可能包括3个方面: 1)氮添加增加了凋落物输入, 促进了碳积累; 2)氮添加减少土壤碳输出, 尤其是抑制了稳定性碳的分解; 3)促进土壤腐殖质及稳定性碳的形成。此外, 该文结合当前研究中存在的不足, 提出今后需加强对深层土壤碳、土壤可溶性有机碳的淋溶及吸附, 以及不同土壤碳组分对氮添加的响应研究, 并通过改进检测方法减少氮添加条件下碳储量的测量误差。