冬季施用鸡粪和生物炭对南方稻田土壤CO2与CH4排放的影响

生物炭的利用近年来是农田土壤固碳减排研究中的热点。本研究通过在冬季稻田养鸡,结合生物炭添加,采用箱式法结合温室气体分析仪定量测定冬季稻田和双季稻期间土壤CO_2和CH_4排放通量,分别估算冬季稻田和双季稻期间土壤CO_2和CH_4排放总量,评估生物炭和鸡粪添加对土壤碳排放的影响。结果表明,鸡粪还田处理显著提高了土壤CO_2的排放,冬季稻田和水稻生育期排放量分别达9 935.39 kg·hm~(-2)和27 756.34kg·hm~(-2),比对照增加58.7倍(P0.01)和56%(P0.05);生物炭添加处理冬季稻田和水稻生育期CO_2累积排放量比对照高12.3倍(P0.01)和41%(P0.05)。鸡粪还田处理下冬季稻田和水稻生育期稻田的CH_4排放量均显著高于其他处理;而生物碳添加对冬季稻田CH_4排放无显著影响,但显著降低了水稻生育期稻田的CH_4排放。鸡粪还田配施生物炭处理也显著提高了稻田土壤CO_2的排放。冬季稻田时,鸡粪还田配施生物炭土壤CO_2累积排放量显著高于鸡粪还田处理;而水稻生育期时,鸡粪还田配施生物炭处理下土壤CO_2累积排放量显著低于鸡粪还田处理。鸡粪还田下添加生物碳可以降低因鸡粪还田引起的CH_4排放增加的效应。总之,鸡粪原位还田显著增加了冬季稻田和水稻生育期稻田的CO_2和CH_4排放;无论是冬季稻田还是水稻生育期,生物炭的添加都降低了土壤CH_4的排放,且生物炭添加后期有抑制土壤CO_2排放的作用。因此,从更长的时间尺度来看,生物炭施入土壤有利于土壤固碳减排。     

PCR—DGGE法研究福建省稻田土壤微生物地区多态性

运用细菌16S rDNA基因和固氮细菌nifH基因的特异引物对,将稻田土壤中提取的总DNA进行PCR扩增后,通过DGGE技术对PCR产物进行分析,以揭示福建省稻田微生物地区多态性。结果表明：福建省不同地区的稻田土壤中,细菌与固氮细菌的组成都有较大差异,且固氮细菌的地区多态性更为明显;同一地区表土与根际土中细菌和固氮细菌的组成也有所不同,尤其是固氮细菌组成在不同地区的表土和根际土间的差异都较大。     

典型菜地土壤剖面N2O、CH4与CO2分布特征研究

为探究菜地土壤剖面N2O、CH4与CO2时空分布特征,利用地下气体原位采集系统与气相色谱法,周年动态监测3种典型菜地,即休闲裸地、轮作地Ⅰ(芹菜?空心菜?小白菜?苋菜)以及轮作地Ⅱ(菜心?芹菜?空心菜?大青菜)7 cm、15 cm、30 cm与50 cm土层N2O、CH4与CO2浓度变化。结果表明,0~50 cm土层范围内,N2O、CH4与CO2 3种气体浓度周年变异性较大,变幅分别为0.63~1 657.0μL(N2O)?L?1、0.8~72.5μL(CH4)?L?1和0.41~36.6 m L(CO2)?L?1。轮作地Ⅰ与轮作地Ⅱ的N2O平均浓度随土壤深度增加而增加,休闲裸地则呈现先增加(0~30 cm)后降低(30~50 cm)的变化趋势。两种轮作菜地4个土层N2O平均浓度均显著高于休闲裸地,二者氮肥施用量不同并未造成相同土层间N2O平均浓度的显著差异。3种菜地CH4与CO2平均浓度均呈现50 cm30 cm15 cm7 cm的梯度特征。轮作地Ⅰ与轮作地Ⅱ0~15 cm土层CH4平均浓度均大于休闲裸地,而在15~50 cm土层则分别大于和小于休闲裸地。CO2浓度呈现明显的季节性变化,除轮作地Ⅰ50 cm土层外,两种轮作菜地其他土层CO2平均浓度均小于休闲裸地对应土层。可见,蔬菜地高氮肥施用、多频次耕作等复杂管理使得N2O、CH4与CO2表现出较大的时空变异特征,其中氮肥施用对N2O的影响大于CH4与CO2,CH4受施肥与耕作的影响均较小,CO2显著受土壤温度与耕作措施的影响,在此基础上需进一步探究N2O、CH4与CO2的其他影响因素。     

太湖地区长期不同施肥水稻土N2和CO2固定细菌群落结构的特征与差异

土壤N2固定细菌和CO2固定细菌是土壤碳氮循环重要的微生物群落,不同施肥下土壤有机碳积累与这两类微生物群落结构及活性的关系有助于了解施肥对农田碳氮循环的影响特点.本文研究了太湖地区自1987年开始的水稻土长期施肥试验,选取不施肥(NF)、氮磷钾(NPK)肥(CF)、NPK肥与猪粪配施(CFM)和NPK肥与秸秆还田配施(CFS)小区,采集(0-20 cm)表层样本,以nifH和cbbLR基因分别作为N2和CO2固定细菌的指示基因,用PCR-DGGE和荧光定量PCR的方法研究二者的群落结构,并用平板菌落计数法测定土壤自生固氮细菌数量和用乙炔还原法测定土壤固氮酶活性.结果表明,与CF处理相比,CF、CFM和CFS处理下的自生固氮细菌数量分别提高了58％、66％和106％;CF、CFM和CFS处理下的nifH基因丰度分别提高了213％、1079％和344％.CF与CFM处理的土壤固氮酶活性显著高于NF和CFS处理.因此,施肥提高了cbbLR基因的多样性.与NF处理相比,CF、CFM和CFS处理下的cbbLR基因丰度分别提高了465％、1827％和758％.相关性分析表明,土壤自生固氮菌数量与土壤有机碳含量呈显著正相关,cbbLR和nifH基因丰度均与归一化的土壤养分呈极其显著正相关.研究表明,有机/无机肥配施下土壤养分平衡对维持N2和CO2固定细菌较高的丰度具有重要的作用.     

三氯生和三氯卡班对水稻土好氧氮转化及N_2O排放的影响

三氯生(Triclosan, TCS)和三氯卡班(Triclocarban, TCC)是典型的药品与个人护理用品,在土壤生态系统中被广泛检出,且存在增加土壤微生物抗药性及抑制土壤呼吸的潜在风险,但目前有关TCS和TCC对土壤氮转化过程及氧化亚氮(N_2O)排放的影响尚不清楚。基于此,采用室内培养实验和15N稀释-富集法,结合氮转化数值模型,研究了不同浓度梯度下TCS(2和5mg·kg~(-1))和TCC(1和2 mg·kg~(-1))的单独及联合存在对水稻土氮初级转化速率以及N_2O排放的影响。结果表明,1mg·kg~(-1)TCC及5mg·kg~(-1)TCS+2mg·kg~(-1)TCC处理对水稻土氮素的矿化-同化无显著影响,其余TCS和TCC处理均显著促进了氮的矿化-同化循环。此外,TCS和TCC处理显著降低了自养硝化速率、硝态氮的微生物固定速率以及硝酸盐异化还原成铵(Dissimilatory nitrate reduction to ammonium, DNRA)速率(2 mg·kg~(-1)TCS处理及5mg·kg~(-1)TCS+2mg·kg~(-1)TCC对DNRA速率无显著影响)。值得关注的是,TCS和TCC单一和联合处理均显著增加了N_2O的累积排放量,其累积排放量为对照的1.13倍～1.44倍。本研究表明,TCS和TCC改变了水稻土好氧氮转化过程,可能对稻田生态系统氮循环产生不利影响;TCC和TCS对水稻土N_2O排放的促进作用也增加了稻田生态系统对温室效应和臭氧层破坏的潜在贡献,因此,未来评价TCS和TCC土壤生态风险时,应考虑其对氮转化过程和N_2O排放的潜在影响。     

温度对贵州喀斯特黄色石灰土有机碳矿化、水稻秸秆激发效应和Q10的影响

为定量揭示温度和秸秆还田对贵州喀斯特黄色石灰土土壤有机碳矿化、激发效应和温度敏感性的影响。以贵州喀斯特地区典型黄色石灰土为研究对象,采用¹³C稳定性同位素标记的水稻秸秆和土壤培养试验研究了15,25,35 ℃培养温度下土壤原有有机碳矿化速率、累积矿化量、激发效应和温度系数Q₁₀对水稻秸秆输入和温度的响应。结果表明:15~35 ℃温度范围和0~60天培养时间内,贵州喀斯特黄色石灰土土壤有机碳、总有机碳、水稻秸秆有机碳和土壤原有有机碳矿化速率均培养1天达到峰值,培养1~30天土壤总有机碳、水稻秸秆有机碳和土壤原有有机碳矿化速率快速下降,30~60天逐渐趋于平缓。温度升高显著增加土壤有机碳、水稻秸秆输入土壤总有机碳、土壤原有有机碳和输入的水稻秸秆有机碳的矿化速率和累积矿化量。培养期间水稻秸秆对土壤有机碳矿化均产生显著正激发效应,且正激发效应随温度升高而强化。培养结束时15,25,35 ℃下其对土壤原有有机碳矿化速率激发效应表现为随温度升高激发效应升高、降低、升高和先升高后降低的温度响应规律,因表征方法不同而不同。15,25,35 ℃培养温度下水稻秸秆对土壤总有机碳矿化速率和累积矿化量的贡献率均随培养时间延长先减小后增大再减小,但2种表征方法和3个培养温度拐点发生时间不同;培养1天时水稻秸秆对土壤总有机碳矿化速率和累积矿化量的贡献率15,25 ℃基本相同且显著高于35 ℃,5天时25,35 ℃基本相当且显著大于15 ℃,其他时间均是25 ℃显著大于35 ℃和35 ℃显著大于15 ℃。15~25 ℃和25~35 ℃ 2个温度体系中水稻秸秆不输入石灰土土壤有机碳矿化速率温度敏感系数Q_10,V分别为1.01~2.60和1.39~3.12,Q_10,F分别为1.50~2.60和1.39~2.17;水稻秸秆输入石灰土土壤总有机碳矿化速率温度敏感系数Q_10,V分别为1.09~2.18和1.05~1.90,Q_10,F分别为1.09~1.73和1.05~1.49;水稻秸秆输入抑制土壤原有有机碳矿化的温度敏感性,水稻秸秆输入导致土壤原有有机碳矿化温度敏感性随温度升高而升高转变为总体上随温度升高而降低在一定程度上可缓冲全球变暖所致的CO₂排放增加。温度对土壤有机碳矿化温度敏感性的影响因表征温度敏感性指标和培养时间长短不同而不同,建立不同培养时间的矿化速率和累积矿化量温度敏感系数的温度函数可精确表征其对温度的响应。研究结果对贵州喀斯特农田土壤秸秆还田、土壤固碳减排、土壤有机碳管理和土壤有机碳库预测等提供参考和借鉴,对丰富土壤有机碳激发效应和温度系数Q₁₀的表征和深入理解具有重要意义。     

太湖地区稻田土壤冬绿肥固氮特性研究

通过田间试验,利用15N自然丰度法评估了太湖地区两种典型水稻土冬季种植紫云英和蚕豆两种绿肥在生长期的固氮特性、固氮量,研究了磷钾肥对紫云英和蚕豆的生物量、固氮率、固氮量的影响。结果表明,两种土壤上,紫云英和蚕豆固氮率在盛花期最高,固氮量在结荚期最高,此时乌栅土紫云英和蚕豆地上部固氮量分别为54.1 kg hm-2和70.8 kg hm-2,另收获的青蚕豆固氮量为38.1 kg hm-2。施磷钾肥能够提高绿肥的生物量和固氮率,从而提高绿肥的固氮量,施磷钾肥分别提高乌栅土紫云英和蚕豆固氮量3.1%和1.7%,垅泥土则分别为98.5%和37.9%。     

北方地区滨海盐渍土型稻田土壤供氮能力的研究

采用短期淹水密闭淋洗培养法(恒温30℃),研究北方地区滨海盐渍土型旱地土壤(种植苜蓿草)开垦种植水稻5年和30年稻田土壤供氮能力。结果表明:(1)3种土壤初始矿质氮主要分布在0~20 cm土层,且土壤初始矿质氮含量的高低顺序为旱地土壤>30年稻田土壤>5年稻田土壤;5年稻田土壤与旱地土壤之间初始矿质氮含量差异达5%显著水平。(2)相同土层,土壤矿化氮量高低顺序为30年稻田土壤>旱地土壤>5年稻田土壤;任意2种土壤之间矿化氮量差异均达1%显著水平。(3)相同土层,土壤供氮能力大小为30年稻田土壤>旱地土壤>5年稻田土壤;其中,在0~20 cm和40~60 cm土层,任意2种土壤之间供氮能力差异均达1%显著水平,在20~40 cm土层,30年稻田土壤与旱地土壤、5年稻田土壤之间供氮能力差异均达1%显著水平,而旱地土壤与5年稻田土壤之间供氮能力则无明显差异。这表明滨海盐渍土型旱地土壤开垦种植水稻后,不仅影响了土壤有机质(氮)含量,而且也影响了土壤有机氮品质,种植水稻5年使土壤供氮能力显著下降,而种植30年使土壤供氮能力显著上升。     

水稻根际土壤及根组织内外固氮微生物的遗传多样性分析

利用PCR—RFLP检测了水稻根际土壤及根组织内外固氮微生物的nifH基因。对54个阳性克隆的nifH 限制性内切酶Mnl I的RFLP图谱进行UPGMA聚类分析和最大似然法分析，结果表明了8对相似的带型(相似性> 50%)和2对同源性为100%的带型分别来源于水稻根际土壤及根组织内外，3种特有的带型均来源水稻根际土壤和3种特有带型来源于水稻根组织内外。证明了水稻根际土壤和水稻根组织的固氮微生物具有显著的多样性，也初步显示了土壤中某些固氮微生物能定植于水稻根内或根表。     

种植大豆对土壤氮素盈亏影响的估算

应用15N示踪方法,研究了种植大豆对土壤氮素盈亏的影响,并对土壤氮素盈亏进行了估算。结果表明:大豆成熟期70.4%~88.6%的氮素转移到籽粒中,大豆氮素收获率很高,导致土壤氮素亏损;秸秆还田时土壤氮素亏损量平均为39.2kg/hm2,秸秆不还田时土壤氮素亏损量平均为49.2kg/hm2;大豆根瘤固氮率与土壤氮素盈亏量呈直线相关,根瘤固氮率越高,土壤氮素亏损量越少;秸秆还田条件下,根瘤固氮率71.5%是土壤氮素盈亏平衡点,秸秆不还田时根瘤固氮率要达到80.9%才能保障土壤氮素盈亏平衡。     

Natural N abundances in a tallgrass prairie ecosystem exposed to 8-y of elevated atmospheric CO2

After 8-y of elevated CO₂, we previously detected greater amounts of total soil nitrogen, suggesting that rates of ecosystem N flux into or out of tallgrass prairie had been altered. Denitrification and associative N fixation rates are the two primary biological processes that are known to control N loss and accumulation in tallgrass prairie soil. Therefore, our objective was to assess the natural abundance of plant and soil ¹⁵N isotopes as a cumulative index of potential change in efflux or influx of N into and out of the tallgrass prairie after 8-y of exposure to elevated CO₂. Aboveground plant delta ¹⁵N values of Andropogon gerardii were close to zero and more positive as a result of elevated CO₂, but whole-soil values at the 5-30 cm depth were significantly reduced (6.8 vs 7.3; P<0.05) under elevated CO₂-chamber (EC) relative to ambient CO₂- chamber (AC). Total, aboveground plant biomass, root-in-growth, extractable N, microbial biomass N, and soil pools collectively exhibited a range of delta ¹⁵N values from −2.8 to 7.3. Measurements of surface soil ¹⁵N indicate that a change in N inputs and outputs has occurred as a result of elevated atmospheric CO₂. In addition to possible changes in denitrification and N₂ fixation, other sources of N such as the re-translocation of N to the surface from deeper soil layers are needed to explain how soil N accrues in surface soils as a consequence of elevated CO₂. Our results support the notion that C accrual may promote N accrual, possibly driven by high plant and microbial N demand amplified by soil N limitation.     

Paddy System with a Hybrid Rice Enhances Cyanobacteria Nostoc and Increases N2 Fixation

Biological nitrogen(N) fixation(BNF) plays a significant role in maintaining soil fertility in paddy field ecosystems. Rice variety influences BNF, but how different rice varieties regulate BNF and associated diazotroph communities has not been quantified. Airtight,field-based ~(15)N_2-labelling growth chamber experiments were used to assess the BNF capacity of different rice varieties. In addition,both the 16 S rRNA and nifH genes were sequenced to assess the influence of different rice varieties on bacterial and diazotrophic communities in paddy soils. After subjecting a rice-soil system to 74 d of continuous airtight, field-based ~(15)N_2 labelling in pots in a growth chamber, the amounts of fixed N were 22.3 and 38.9 kg ha~(-1) in inbred japonica(W23) and hybrid indica(IIY) rice cultivars planted in the rice-soil systems, respectively, and only 1%–2.5% of the fixed N was allocated to the rice plants and weeds. A greater abundance of diazotrophs was found in the surface soil(0–1 cm) under IIY than under W23. Sequencing of the 16 S rRNA gene showed significantly greater abundances of the cyanobacterial genera Nostoc, Anabaena, and Cylindrospermum under IIY than under W23.Sequencing of the nifH gene also showed a significantly greater abundance of Nostoc under IIY than under W23. These results indicate that the hybrid rice cultivar(IIY) promoted BNF to a greater extent than the inbred rice cultivar(W23) and that the increase in BNF might have been due to the enhanced heterocystous cyanobacteria Nostoc.     

基于15N同位素示踪盐渍化农田向日葵氮素利用规律

为探明盐渍化农田不同施氮水平下向日葵氮素吸收利用规律,采用¹⁵N同位素示踪技术进行田间微区试验,以不施氮处理(N0)为对照,设计3种施氮水平(N1=150 kg/hm²、N2=225 kg/hm²、N3=300 kg/hm²),于向日葵成熟期测定植株和0—100 cm土层土壤¹⁵N同位素丰度及总氮含量,研究各处理肥料氮素的去向及其利用机制。结果表明:向日葵氮素吸收量随施氮量的增加而增加,成熟期作物氮素吸收量在N2水平较不施氮显著增加38.7%;土壤氮和肥料氮对作物当季氮素吸收的贡献比例为84.9%和15.1%。N2水平下,肥料氮的贡献比例较N1增加35.7%,土壤氮的贡献比例较N1降低4.3%。肥料氮残留量随土层深度增加而减少,土壤中47.4%的残留肥料氮主要集中在0—20 cm土层。不同施氮水平下肥料氮去向均表现为氮肥损失率>氮肥残留率>氮肥利用率,N2施氮水平下氮肥利用率较N1、N3显著提高22.7%和14.6%,土壤残留率较N1、N3减少8.5%和8.6%。综合考虑向日葵氮素吸收利用及土壤中氮素残留情况,225 kg/hm²施氮量下氮肥利用率为27.4%,氮肥残留率为32.3%,氮肥损失率为40.3%,是中度盐渍化农田较适宜的施氮量。     

Evaluation of N2 fixation by applying 15N labeled plant material and ammonium sulfate

Effect of different ¹⁵N labeled sources on the estimation of N₂ fixation was investigated. The combination of ¹⁵N labeled ammonium sulfate, ¹⁵N labeled plant material, and ¹⁵N labeled ammonium sulfate with unlabeled plant material, was examined in pot experiments. Two cultivars of soybean (Glycine max) and one of mungbean (Vigna radiata) were used. No significant difference was observed among the treatments for the estimation of N₂ fixation. This was due to the homogeneity and stability of the ¹⁵N abundance in soil which resulted in a similar N uptake from the soil by the N² fixing and reference crops. The plant yield, total N uptake and amount of N₂ fixed were higher in the Yellow Soil than in the Andosol. The amount of N₂ fixed was strongly influenced by the plant growth and consequently it affected the plant yield. The slow decomposition of plant material in the Andosol resulted in a low yield in both the N₂ fixing and reference crops. Thus, the artificial decrease of the available N content in soil, by application of plant material, did not stimulate N, fixation but suppressed plant growth and N₂ fixation.     

华北平原玉米种植中施入氮肥的去向研究

为了定量研究玉米氮肥利用特性以及肥料氮的去向,设计了~(15) N标记微区控制试验,设置3个施氮水平:不施氮肥(对照)、低氮处理(120kg N/hm~2)和高氮处理(240kg N/hm~2)。结果表明:土壤中残留~(15) N量随施氮量增加而显著增加(P0.05)。在空间分布上,总体呈现出随土壤深度先下降后上升的趋势,高氮处理和低氮处理~(15) N累积量均以40—60cm和60—80cm土层最多,这两层残留~(15) N总量分别占总投入量的37.55%和18.99%。与对照相比,施氮处理均显著提高了玉米地上、地下生物量和籽粒产量以及各部分吸氮量。虽然高氮处理较低氮处理施氮量增加了1倍,但籽粒产量仅增加0.14倍。氮肥农学效率与氮肥表观利用率随着施氮量增加而显著降低。高氮处理和低氮处理中玉米对~(15) N标记氮肥的利用率分别为28.86%和31.15%,土壤氮残留率分别为50.42%和36.52%,当季进入地下水的比率分别为4.27%和0.68%,其他损失率分别为16.45%和32.33%。研究结果表明,施氮量为120kg/hm~2可有效增加玉米产量,同时提高氮肥利用率,减少土壤氮累积,减小氮肥施用产生的环境污染风险。     

移栽叶龄对水稻氮素吸收利用及~(15)N-肥料去向影响

利用15N示踪技术研究了不同叶龄移栽对水稻产量、氮肥吸收利用及其氮素去向的差异。结果表明,随移栽叶龄推迟,水稻产量显著降低,籽粒与秸秆氮肥吸收量、肥料利用率及其残留量也降低,而氮素损失增加。水稻所吸收的氮素约2/3来源于土壤氮,1/3来源于当季肥料施的氮。肥料利用率为20.8%~25.7%,氮肥残留率为17.9%~32.2%,有42.1%~61.3%的肥料损失。无论哪种叶龄移栽条件下,肥料主要残留在0~20cm土层中。研究表明水稻早栽能增加产量、提高肥料利用率,减少肥料损失,降低氮素对环境的污染。     

连续翻压紫云英对福建单季稻产量与化肥氮素吸收、分配及残留的影响

【目的】紫云英翻压后在一定程度上可改善土壤理化性状,并提高后作水稻的产量,但是该机理是由于紫云英翻压矿化后提供的氮素还是由于与翻压紫云英后化肥氮素利用率的提高有关尚不清楚,因此,本项目通过连续4年紫云英翻压还田的定位试验与原状土柱模拟及15N示踪,研究了福建单季稻区紫云英压青回田对水稻产量与化肥15N吸收、 分配及残留的影响。【方法】采用单季稻田间定位试验,设5个处理: 1）对照,不翻压紫云英,不施化肥（CK）;2）不翻压紫云英,常规化肥施用量（100%H）;3）紫云英＋常规化肥用量（Z+100%H）;4）紫云英＋60%的常规化肥（Z+60%H）;5）只翻压紫云英,不施化肥（Z）。常规化肥用量（100%H）为施氮量N 135 kg/hm2,N∶P2O5∶K2O=1∶0.4∶0.7,每年紫云英翻压量为18000 kg/hm2。每个处理3次重复,小区面积15 m2,种植水稻为每小区2015丛。于定位试验的第4年,在田间定位试验小区中,采用15N-尿素（丰度10%）示踪法与原状土柱模拟水稻植株的氮素吸收及分配情况。PVC管直径25 cm,长35 cm,其中压入田面下20 cm,每小区埋两个土柱,每个土柱中种植两株水稻。【结果】紫云英年翻压18000 kg/hm2并结合施用100%化肥（Z+100%H）,水稻子粒4年平均产量比单施100%化肥（100%H）增产6.5%,同时在18000 kg/hm2 的紫云英翻压量下,主作物水稻化肥减量40%（Z+60%H）的产量与100%H的处理基本相当。Z+100%H处理对提高水稻分蘖期植株氮含量最为明显,尤其是茎叶氮含量较100%H提高7.0%,差异显著。虽然不同施肥处理水稻生育期的化肥氮素利用率无明显变化,但Z+100%H处理分蘖期与成熟期植株氮素吸收量分别较100%H提高23.0%与18.0%,说明绿肥与化肥配施有利于水稻植株吸收外源氮素,且植株吸收氮的差异主要来自于紫云英矿化的氮源。Z+60%H 与100%H处理的分蘖期与成熟期植株氮素吸收量则基本相当。不同施肥处理均有提高土壤全氮含量的趋势;Z+60%H 处理的耕层土壤化肥氮素的残留率最高,并显著高于Z+100%H处理。【结论】连续4年翻压紫云英明显提高了福建单季稻区黄泥田的农田生产力,在减少40%常规化肥用量的情况下仍可维持产量稳定。翻压绿肥减肥增效的主要机制之一是紫云英矿化的养分替代了化肥。     

利用15N揭示滴灌区盐旱胁迫对土壤氮素分布与棉花生长的影响

为了探究盐旱胁迫对土壤中氮素分布和棉花生长的影响,通过测坑试验研究滴灌区不同盐分、干旱条件下土壤全氮、硝氮、氨氮的分布和棉花生长情况。试验设置3种盐分梯度的土壤（电导率,EC）：3,6,9 dS/m,分别用T1、T2、T3表示;3个灌水量：2 700,3 600,4 500 m³/hm²,分别用W1、W2、W3表示（4 500 m³/hm²为当地推荐灌水量）。结果表明：当土壤盐分梯度> 3 dS/m时土壤全氮累积量显著高于低盐土壤（P<0.05）,且土壤盐分对棉花花期生长影响较大。土壤的氨氮挥发量和土壤盐分梯度成正比。土壤硝态氮的淋失与灌水量呈正比,与正常灌水量的硝态氮淋失相比,水分胁迫对棉花产量的影响更为严重（P<0.01）。随土层深度的增加,土壤碱解氮以每20 cm土层8%的速度减少。各处理土壤¹⁵N残留率为11%~40%,随土壤盐度增加而增加,随灌水量增加而减少,与土壤全氮含量呈正比,与棉花产量呈反比。综上所述,T1W3处理更有利于棉花对氮肥的利用和产量的提高,推荐滴灌区棉花土壤盐度<3 dS/m,灌水量4 500 m³/hm²,可在花期适当提高施肥量以稳定产量。     

黄绵土与淋溶土含水量与施肥方法对铵固定和肥料氮回收率的影响

Ammonium fixation and the effects of soil moisture and application methods on fertilizer N recovery were investigatedin two soils of Shaanxi Province, China, a Luvisol and an Entisol, through two experiments performed in the laboratoryand in a glass shelter, respectively, by using ammonium bicarbonate (NH4HCO3). The laboratory closed incubationbox experiment was conducted using the Luvisol to study NH fixation rate at soil moisture levels of 10.1%, 22.7% and 35.3% water filled pore space (WFPS). The fixed NH -N increased dramatically to 51% and 66%, 67% and 74%,and 82% and 85% 1, 2 and 36 h after fertilizer incorporation at moisture levels of 10.1% and 22.7% WFPS and 35.3% WFPS, respectively. The rapid NH fixation rates at all moisture levels could help prevent NH losses from ammonia volatilization. In the glass shelter pot experiment, N fertilizer was applied by either banding (in a concentrated strip)or incorporating (thoroughly mixing) with the Entisol and the Luvisol. An average of 74.2% of the added N fertilizerwas recovered 26 days after application to the Luvisol, while only 61.4% could be recovered from the Entisol, due tohigher NH fixation capacity of the Luvisol. The amount of fixed NH decreased with increasing WFPS. The amountof fixed NH in the incorporated fertilizer treatment was, oll average, 10% higher than that in the banded treatment.Higher NH fixation rates could prevent N loss and thus increase N recovery. The results from the Luvisol showed lowernitrogen recovery as soil moisture level increased, which could be explained by the fact that most of the fixed NH wasstill not released when the soil moisture level was low. When the fertilizer was incorporated into the soil, the recovery ofN increased, compared with the banded treatment, by an average of 26.2% in the Luvisol and 11.2% in the Entisol, whichimplied that when farmers applied fertilizer, it would be best to mix it well with the soil.     

15N标记的土壤估测某些豆科植物N2固定的温室实验

Pot experiments were carried out to estimate N2 fixation by vetch,milk vetch,sickle alfalfa and broadbean in pure stand using a ^15N-labelled soil.Winter wheat was used as the non-fixing control.The 15N-labelled soil used was prepared by growing corn-wheat-corn successively on a nearly organic-matter-free Xiashu loess supplemented with adequate amounts of (15NH4)2SO4,P,K and micronutrients,then incorporating these 15N-labelled plant materials into the soil after each havest,and allowing the plant materials to be decomposed aerobically for 410d after incorporation of the plant material of the thire crop.The 15N enrichment of wheat plant-N varied slightly with organs,with a maximum difference of 9.8%,Based on 15N enrichment of soil N inferred from the mean value of the 15N enrichment in different organs of wheat 79%-91% of total N in the tops and 67%-74% of total N in the roots of legumes studied were derived from atmosphere .Estimate by isotope dilution method was in good agreement with that by the conventional difference method provided values obtained by the latter were corrected for seed N,and also with that from the measurement of N accumulated in the tops of the legumes.