Humic Acid Effects on Reducing Corn Leaf Burn Caused by Foliar Spray of Urea-Ammonium Nitrate at Different Humic Acid/Urea-Ammonium Nitrate Ratios

Technologies for reducing corn leaf burn caused by foliar spray of urea-ammonium nitrate (UAN) during the early growing season are limited. A field experiment was carried out to evaluate the effects of humic acid on corn leaf burn caused by foliar spray of undiluted UAN solution on corn canopy at Jackson, TN in 2018. Thirteen treatments of the mixtures of UAN and humic acid were evaluated at V6 of corn with different UAN application rates and different UAN/humic acid ratios. Leaf burn during 1 2, 3, 4, 5, 6, 7, and 14 days after UAN foliar spray significantly differed between with or without humic acid addition. The addition of humic acid to UAN significantly reduced leaf burn at each UAN application rate (15, 25, and 35 gal/acre). The reduction of leaf burn was enhanced as the humic acid/UAN ratio went up from 10% to 30%. Leaf burn due to foliar application of UAN became severer with higher UAN rates. The linear regression of leaf burn 14 days after application with humic acid/UAN ratio was highly significant and negative. However, the linear regression of leaf burn 14 days after application with the UAN application rate was highly significant and positive. In conclusion, adding humic acid to foliar-applied UAN is beneficial for reducing corn leaf burn during the early growing season.

In situ Detection of Amide A Bands of Proteins in Water by Raman Ratio Spectrum

The amide A band of protein is sensitive to the hydrogen bands of amide groups of proteins. However, it is hard to distinguish the amide A band of aqueous protein in situ directly, since it overlaps with O-H stretching vibration of water. In this work, we presented a new analytical method of Raman ratio spectrum, which can extract the amide A band of proteins in water. To obtain the Raman ratio spectrum, the Raman spectrum of aqueous protein was divided by that of pure water. A mathematical simulation was employed to examine whether Raman ratio spectrum is effective. Two kinds of protein, lysozyme and （^-chymotrypsin were employed. The amide A bands of them in water were extracted from Raman ratio spectra. Additionally, the process of thermal denaturation of lysozyme was detected from Raman ratio spectrum. These results demonstrated the Raman ratio spectra could be employed to study the amide A modes of proteins in water.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

INTERACTIONS BETWEEN AMMONIUM UPTAKE AND NITRATE UPTAKE BY NATURAL PHYTOPLANKTONASSEMBLAGES

Measurements of ammonium and nitrate uptakes by natural phytoplankton assemblages from Jiaozhou Bay at various combinations of ammonium and nitrate concentrations with 15N trace techniques showed that uptake rate of either nitrogen was influenced by the presence of the other but that the influence of ammonium on nitrate uptake was much greater than, that of nitrate on ammonium uptake. The influence mechanism of ammonium on nitrate uptake manifested as competition at lower concentrations and as inhibition at higher concentrations (ammonium concentration 】0.6 umol/L), but no total inhibition appeared within the concentration.range of the experiments (0-10umol/L). The influence of nitrate on ammonium uptake seems to be a result of competition for uptake sites on the cell surface. In view of the in situ nutrient concentration in the given marine . environment, it is believed that both nitrogen sources are utilized by phytoplankton. Nitrate uptake in the presence of ammonium and ammonium uptake in the

Packaging category and its influencing factors of potassium nitrate

To understand the combustion characteristics of potassium nitrate and evaluate the magnitude of combustion risk, ox-idation solid test apparatus is used and the updated experimental criterion of the United Nations is adopted to measure the pack-aging category of potassium nitrate. The new criterion puts calcium peroxide and microcrystalline cellulose as references and burning rate as evaluation index. Effects of mixing ratio and insert medium on burning rate are reached. Test results show that pure potassium nitrate doesn＇t burn under normal temperature and pressure, however, its oxidation is very strong and the packaging category should choose the class I. As the mass fraction of potassium nitrate reduces, the burning rate first increases and then decreases. When the ratio is 2 ： 1,the combustion rate reaches the maximum, and the effect of combustion is the best. When 1 ： 3, the combustion rate is the minimum. The mixture combustion can be suppressed by silicon dioxide and hy-drogen phosphate, which is not fired when silica concentration is 40% or ammonium hydrogen potassium phosphate is 55%, their effects are very obvious.

Effects of Co-Existing Ions on the Phosphorus Potassium Ratio of the Precipitate Formed in the Potassium Phosphate Crystallization Process

Livestock wastewater is mainly treated with activated sludge, but ions such as phosphorus, potassium, ammonium, nitrate and sulfate remain in the effluent. In this study, the effects of residual ions on phosphorus recovery using the magnesium potassium phosphate crystallization method were investigated when magnesium was added to increase the pH. If co-existing ions affect the products, the phosphorus to potassium molar ratio (K/P ratio) of the precipitate will deviate from being equimolar. Artificial wastewater test solutions containing 5.6 - 20.3 mM ammonium, 25.6 mM potassium, 6.5 mM phosphorus, 0 - 7.35 mM nitrate, and 0 - 3.06 mM sulfate were used. First, the optimum operating pH and amount of magnesium added to give a high phosphorus removal rate and recovery rate were determined. The experimental setup was a 10 L aerated and stirred reactor, and a 5 L settling tank. The K/P ratio in precipitate was approximately 1 using the optimum conditions. Continuous 2 h treatment allowed a white precipitate containing about 30 g of needle-like crystals to be obtained. Next, the effects of varying the ammonium, nitrate, and sulfate ion concentrations in the artificial effluent were investigated. Ammonium and sulfate ion concentrations of 8 mM or more and 3 mM or more, respectively, caused the K/P ratio to decrease to about 0.7 and 0.5, respectively. Varying the nitrate concentration did not affect the K/P ratio, even at a nitrate concentration of 7.35 mM.

硝态氮对设施番茄产量与品质的影响

为探究硝态氮合理替代酰胺态氮对提高设施蔬菜氮素利用率、产量及品质的作用,本试验以设施番茄(Solanum lycopersicum L.)为研究对象,在等氮条件下,设置不同比例的硝态氮替代酰胺态氮处理,NO_(3)^(-)-N∶CO(NH_(2))_(2)-N依次为0∶100(T1)、25∶75(T2)、50∶50(T3)、75∶25(T4)、100∶0(T5),分析不同比例硝态氮处理对设施番茄氮素积累量、产量和品质等的影响,以及氮相关转化酶活性的响应规律。结果表明,与T1和T5处理相比,硝态氮替代50%~75%酰胺态氮(T3~T4)处理的各生育期硝酸还原酶(NR)和谷氨酰胺合成酶(GS)活性较高,促进了设施番茄全生育期氮素转化和叶绿素合成,提高了净光合速率,使氮素积累量增加12.82%~20.98%,地上部干物质量增加6.51%~24.16%,产量提高9.41%~26.62%。二次拟合曲线结果表明,硝态氮替代酰胺态氮比例为60.37%时的设施番茄产量达到最高,为77.95 t·hm^(-2)。与T1和T5处理相比,硝态氮替代50%~75%时,设施番茄可溶性固形物、维生素C、还原糖、可溶性糖含量和糖酸比分别提高7.96%~13.51%、10.81%~14.27%、11.11%~16.38%、26.25%~35.67%和27.37%~49.06%,硝酸盐和有机酸含量分别降低21.72%~33.75%和10.73%~22.22%,番茄品质达到最佳。相关性分析结果表明,净光合速率、产量、果实可溶性糖和还原糖含量等与氮素积累量、NR、GS活性呈显著或极显著正相关关系,说明施用硝态氮可通过提高氮转化关键酶活性而提高番茄氮素利用率,进而达到增产提质的目的。综上所述,硝态氮替代60.37%酰胺态氮是设施番茄生产的最佳施肥模式,可有效提高设施番茄产量及品质。本研究结果为实现设施番茄高产优质栽培提供了理论依据和技术参考。

硝铵供应比对油菜光合作用的影响

【目的】油菜是我国重要的油料作物,当铵态氮(NH_(4)^(+)-N)作为唯一氮源时,油菜的光合作用受到显著抑制,添加硝态氮(NO_(3)^(−)-N)能显著缓解NH_(4)^(+)-N的抑制效应。探究不同硝铵配比对油菜叶片光合能力的影响,明确硝态氮调控油菜光合能力的生理机制,对优化施用氮肥形态,保障冬油菜扩面增产有重要意义。【方法】利用水培试验方法,在高氮(8 mmol/L,HN)和低氮(1 mmol/L,LN)处理下,设置全硝、硝铵3∶1、硝铵1∶1、硝铵1∶3、全铵5个配合比例,在处理15、20、25天时,取油菜样品,测定光合能力参数和生物量。利用光合限制模型分析硝铵比对光合速率的限制。【结果】全铵处理的油菜在HN处理下第5天和LN处理下第7天开始出现枯黄症状,直至18天全部死亡,在处理15天后,植株生物量差异显著。与硝铵3∶1相比,硝铵1∶1处理生物量降低了5.6%~61.3%,硝铵1∶3处理下降了6.9%~110.6%。同一氮水平下,不同硝铵比例叶片全氮含量无显著差异,然而硝态氮和铵态氮含量差异显著,硝铵3∶1处理叶片硝态氮含量显著高于硝铵1∶1和1∶3处理,分别高出91.7%~292.7%和130.0%~1255.0%;而叶片铵态氮含量在生长后期以硝铵1∶3配比显著高于硝铵3∶1和全硝处理,分别高出52.6%~53.3%和61.1%~76.9%。硝态氮添加显著提高叶片净光合速率(A),硝铵3∶1配比的A最高,较硝铵1∶1和1∶3配比的A显著提高了16.7%~50.3%;硝铵3∶1处理显著提高了最大净光合速率(Amax)、最大羧化速率(Vcmax)、最大电子传递速率(Jmax)和叶肉导度(gm),分别提高了6.8%~107.4%、9.2%~79.5%、50.5%~115.8%和8.6%~134.8%。A随叶片硝态氮浓度和硝态铵态氮含量比值增加而增加,在硝态氮含量超过120.2~151.2μg/g,比值超过2.6~3.2后,不再显著变化。通过光合限制模型分析,硝态氮添加提高油菜光合速率是通过降低生化限制和叶肉导度限制。【结论】适当提高油菜氮肥的硝铵比可促进叶片的gm、Vcmax,从而提高叶片光合能力和植株生物量。氮源中铵超过一半后抑制油菜的光合作用,甚至导致油菜不能完成生命周期,而100%硝态氮也不利于油菜的光合作用。

高原鼢鼠驱动高寒草甸土壤碳氮含量变化的时效性

为明确小型地下啮齿动物鼠丘效应和边缘效应影响土壤碳氮含量的时效性,本研究采用分区取样法研究青藏高原东北缘高寒草甸0~20 cm土层有机碳和氮随高原鼢鼠(Eospalax baileyi)鼠丘恢复年限的变化特征。结果表明:鼠丘效应影响土壤有机碳、全氮、铵态氮、硝态氮含量及C∶N和铵态氮/硝态氮(ANR),具有明显的时效性。其中,鼠丘不同土层的有机碳含量、0~10 cm土层的铵态氮含量和C∶N在第4年时恢复至对照区水平,鼠丘0~10 cm土层的全氮、硝态氮含量和ANR在第3年时恢复至对照区水平;10~20 cm土层,鼠丘土壤硝态氮和铵态氮含量在第5年恢复至对照区水平,土壤全氮在第1年恢复至对照区水平。边缘效应影响土壤有机碳、全氮、铵态氮和硝态氮含量及C∶N,亦表现出明显的时效性。其中,边缘区不同土层的铵态氮含量在第4年时恢复至对照区水平;0~10 cm土层,边缘区的土壤硝态氮、有机碳含量在第3年时恢复至对照区水平,土壤全氮含量和C∶N在第5年恢复至对照区水平;边缘区10~20 cm土层的硝态氮含量在第2年恢复至对照区水平。

多形态氮和硝化抑制剂协同供应对土壤氮素转化的影响

氮养分增效对提高作物产量、品质具有重要意义,其中铵硝协同的养分形态调控策略是手段之一。为探究有机氮无机氮源配施、施用硝化抑制剂两种养分动态调控手段对土壤铵硝动态的影响,采用室内土壤培养试验,设置不同比例的硫硝酸铵和草酰胺配施处理5个,硫硝酸铵:草酰胺比例分别为100%:0%、0%:100%、25%:75%、50%:50%、75%:25%,每组处理另设置添加硝化抑制剂3,4-二甲基吡唑磷酸盐(DMPP)处理,用以探究不同氮源配施抑制剂DMPP处理对潮土(pH8.25)和水稻土(pH5.48)氮素转化的影响。结果表明,缓释氮肥草酰胺与硫硝酸铵配施显著影响土壤铵硝养分供应形式和速率。直至第10d培养结束,缓释氮肥草酰胺在土壤中的铵、硝态氮仍呈现一个较高水平。抑制剂DMPP的添加可提高所有处理的铵态氮含量,降低硝态氮含量,提高土壤铵硝比,降低土壤表观硝化率。综上所述,草酰胺与硫硝酸铵的不同比例以及配施抑制剂DMPP的方式可以实现对土壤中铵硝比例的改变,提高肥料利用率。

Combined effects of volume ratio and nitrate recycling ratio on nutrient removal,sludge characteristic and microbial evolution for DPR optimization

The optimization of volume ratio(V_(An)/V_(A)/V_(0))and nitrate recycling ratio(R)in a two-sludge denitrifying phosphorus removal(DPR)process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor(A^(2)/O-MBBR)was investigated.The results showed that prolonged anaerobic retention time(HRT An:1.25→3.75 hr)exerted favorable effect on chemical oxygen demand(COD)removal(57.26%→73.54%),poly-β-hydroxyalkanoates(PHA)synthesis(105.70→138.12 mg COD/L)and PO_(4)^(3-)release(22.3→38.9 mg/L).However,anoxic retention time(HRT A)and R exhibited positive correlation with PHA utilization(43.87%-81.34%)and denitrifying phosphorus removal(DPR)potential(NO_(3)-/PO^(3-)_(4):0.57-1.34 mg/mg),leading to dramatical TN removal variations from 68.86%to 81.28%.Under the V An/V A/V O ratio of 2:6:0,sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered.The sludge characteristic and microstructure gradually transformed under the dissolved oxygen(DO)control(1.0-1.5→1.5-2.0 mg/L),in terms of sludge volume index(SVI:194→57 m L/g VSS),median-particle-size(D 50:99.6→300.5μm),extracellular polymeric substances(EPS)(105.62→226.18 mg/g VSS)and proteins/polysaccharides(PN/PS)ratio(1.52→3.46).Fluorescence in situ hybridization(FISH)results showed that phosphorus accumulation organisms(PAOs)(mainly Cluster I of Accumulibacter,contribution ratio:91.79%-94.10%)dominated the superior DPR performance,while glycogen accumulating organisms(GAOs)(mainly Competibacter,contribution ratio:82.61%-86.89%)was responsible for deteriorative TN and PO_(4)^(3-)removals.The optimal HRT A and R assembled around 5-6.5 hr and 300%-400%based on the PHA utilization and DRP performance,and the oxic zones also contributed to PO_(4)^(3-)removal although it showed low dependence on DO concentration and oxic retention time(HRT_(0)).

Effects of C/N ratio on nitrate removal and floc morphology of autohydrogenotrophic bacteria in a nitrate-containing wastewater treatment process

The effects of C/N ratio of a nitrate-containing wastewater on nitrate removal performed by autohydrogenotrophic bacteria as well as on the morphological parameters of floc such as floc morphology, floc number distribution, mean particle size（MPS）, aspect ratio and transparency were examined in this study. The results showed that the nitrate reduction rate increased with increasing C/N ratio from 0.5 to 10 and that the nitrogen removal of up to 95% was found at the C/N ratios of higher than 5（between 0.5–10）. Besides, high C/N ratio values reflected a corresponding high nitrite accumulation after 12-hr operation, and a fast decreasing rate of nitrite in the rest of operational time. The final p H values increased with the C/N ratio increasing from 0.5 to 2.5, but decreased with the C/N ratio increasing from2.5 to 10. There were no significant changes in floc morphology with the MPSs ranging from35 to 40 μm. Small and medium-sized flocs were dominant in the sludge suspension, and the number of flocs increased with the increasing C/N ratios. Furthermore, the highest apparent frequency of 10% was observed at aspect ratios of 0.5 and 0.6, while the transparency of flocs changed from 0.1 to 0.7.

Optimization of denitrifying phosphorus removal in a predenitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system:Nitrate recycling,carbon/nitrogen ratio and carbon source type

Because the efficiency of biological nutrient removal is always limited by the deficient carbon source for the low carbon/nitrogen(C/N)ratio in real domestic sewage,the denitrifying phosphorus removal(DNPR)was developed as a simple and efficient method to remove nitrogen and phosphorous.In addition,this method has the advantage of saving aeration energy while reducing the sludge production.In this context,a pre-denitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system,which could also reduce high ammonia effluent concentration in the traditional two-sludge DNPR process,is proposed in this work.The pre-A_(2)NSBR process was mainly composed of a DNPR SBR and a nitrifying SBR,operating as alternating anaerobic/anoxic/post-aeration+nitrification sequence.Herein,the long-term performance of different nitrate recycling ratios(0-300%)and C/N ratios(2.5-8.8),carbon source type,and functional microbial community were studied.The results showed that the removal efficiency of total inorganic nitrogen(TIN,including NH4^(+)-N,NO_(2)^(-)-N,and NO_(3)^(-)-N)gradually increased with the nitrate recycling ratios,and the system reached the highest DNPR efficiency of 94.45% at the nitrate recycling ratio of 300%.The optimum C/N ratio was around 3.9-7.3 with a nitrogen and phosphorus removal efficiency of 80.15%and 93.57%,respectively.The acetate was proved to be a high-quality carbon source for DNPR process.The results of fluorescence in situ hybridization(FISH)analysis indicated that nitrifiers and phosphorus accumulating organisms(PAOs)were accumulated with a proportion of 19.41%and 26.48%,respectively.

“离子交换法”测定硝酸盐氧同位素组成方法的改进

硝酸盐氮、氧同位素组成(δ^(15)N、δ^(18)O)被广泛应用于识别水体中硝酸盐的来源及其生化转化过程.离子交换技术作为主要分析方法之一,被大量应用于测定硝酸盐的氮同位素组成,然而在测定氧同位素组成时,由于该方法的样品处理过程复杂繁琐、耗时长(3~5天)等缺点限制了它的广泛应用.通过对原技术路线进行改进:将定量的BaCl_(2)直接加入到野外采集的水样中,消除含氧阴离子(SO_(4)^(2-)和PO_(4)^(3-))对测定NO_(3)^(-)离子δ^(18)O的干扰,然后再通过阴离子交换树脂吸附富集、HCl洗脱NO_(3)^(-)、Ag_(2)O中和,得到用于测试δ^(18)O的AgNO_(3)样品.与原路线相比,改进后方法的优势在于:(1)样品处理步骤由原来的5步缩短到了3步;(2)样品处理时长由3~5天缩短至1~2天;(3)减少了昂贵的化学试剂的用量;(4)减少了同位素的分馏.

栽培基质pH和铵硝氮比对杉木木荷氮代谢酶及氮含量的影响

【目的】探究栽培基质pH和铵硝态氮配比对亚热带主要针叶树杉木和阔叶树木荷幼苗叶片氮代谢酶活性及植株氮含量的影响。【方法】设置栽培基质为2个pH水平(pH_(1)=4.5和pH_(2)=6.5)和3个铵硝态氮配比(NH_(4)^(+)-N∶NO_(3)^(-)-N分别为10∶0、0∶10、5∶5),分析和比较2个树种幼苗叶片的谷氨酰胺合成酶(GS)、谷氨酸合成酶(GOGAT)、硝酸还原酶(NR)和亚硝酸还原酶(NiR)活性及各器官氮含量差异。【结果】(1)与基质pH=6.5相比,pH=4.5抑制了杉木和木荷叶中氮代谢酶GS、GOGAT、NR和NiR的活性,增加了杉木根、茎、叶中的铵态氮含量,降低了杉木各器官中的硝态氮含量和总氮素积累量,降低了0∶10配比下木荷叶的氮素积累量。(2)10∶0配比显著增加杉木叶中的氮代谢酶活性和pH=4.5处理下木荷叶中的氮代谢酶活性、增加pH=6.5处理下木荷根和叶中的铵态氮含量、木荷根的硝态氮含量及杉木茎叶及总的氮素积累量。5∶5配比显著增加pH=4.5处理下木荷根中硝态氮含量。0∶10配比显著增加pH=4.5处理下杉木叶中的铵态氮含量,增加pH=6.5处理下木荷叶的NiR活性,木荷茎叶和总氮积累量。(3)在同一处理下,杉木叶中的氮代谢酶活性均低于木荷,表明木荷具有比杉木更强的同化氮素的能力。(4)相关性分析表明,杉木总氮素积累量与氮代谢酶活性、根的硝态氮含量呈显著正相关,与器官铵态氮含量呈显著负相关,木荷总氮素积累量与叶铵态氮含量呈显著负相关。【结论】栽培基质pH为4.5的栽培环境不利于杉木和木荷幼苗对氮素的吸收,铵态氮添加可促进杉木的氮素积累,而硝态氮添加可促进木荷的氮素积累。故在生产中应综合考虑栽培基质的pH和树种特性等因素选择适宜的铵硝态氮比例进行杉木和木荷幼苗及林地的氮素营养管理。

磷对小麦利用土壤深层累积硝态氮的影响

【目的】在粮食主产区华北平原,研究磷对小麦利用土壤深层累积硝态氮的影响。【方法】采用15N微区注射技术,布置田间微区试验,将15N标记于110cm土层处。【结果】在本试验条件下,小麦能够利用注射并扩散于100～120cm土壤层次的标记硝态氮,3种磷水平的利用率分别为6.8%、16.4%和11.2%;耕层施用磷肥有利于小麦地下部根系发育,根长密度及根干重较不施磷均有增加,提高了小麦对深层硝态氮的利用,耕层适量供磷有利于小麦对土壤剖面深层标记硝态氮的吸收利用。【结论】磷促进小麦根系发育,提高小麦对土壤深层累积硝态氮的利用,过量施磷起抑制作用。

氮素形态对菠菜可食部分硝酸盐和草酸累积的影响

采用溶液培养试验研究了营养液中硝态氮／铵态氮比例对菠菜地上部可食部分不同器官硝酸盐以及不同形态草酸累积的影响。结果表明，菠菜地上部生物量随供铵比例从0％提高到50％呈增加趋势而后显著下降。叶片和地上部可食部分的硝酸盐含量和累积量均随供铵比例增加而显著下降；叶柄的硝酸盐含量随供铵比例提高而降低，而硝酸盐积累量则先升高后显著下降。叶片是菠菜积累草酸的主要器官，可溶态草酸与草酸总量分别占地上部的56．3％～89．8％和76．6％～87．4％。可溶态草酸是菠菜体内草酸的主要形态，在叶片、叶柄及地上部中所占草酸总量的比例分别在36．7％～83．5％，79．0％～93．3％以及50．0％～83．0％之间。地上部各器官的可溶态草酸含量、难溶态草酸含量和草酸总量以及积累量均随着供铵比例的增加而显著下降，叶片和地上部的草酸含量和积累量的下降幅度均高于叶柄。可见，调节营养液中硝态氮／铵态氮比例可以有效降低菠菜地上部可食部分硝酸盐和草酸的含量和积累量，50／50是营养液中适宜的硝态氮／铵态氮比例，不仅菠菜的生物量最高，而且硝酸盐和各形态草酸的含量以及累积量较低，从而大大减轻了硝酸盐和草酸对人体健康产生的负面影响。

耕层水氮调控对小麦利用土壤深层累积硝态氮的影响

【目的】研究华北平原耕层水氮调控对小麦利用土壤深层累积硝态氮的影响。【方法】设置0、150kgN·hm-22个氮水平和传统灌溉、优化灌溉2种灌水方式,共4个处理:不施氮传统灌溉(N0W1)、不施氮优化灌溉(N0W2)、施氮传统灌溉(N150W1)、施氮优化灌溉(N150W2)。采用15N微区注射技术,布置田间微区试验,将15N标记于110cm土层处。【结果】在本试验条件下,小麦能够吸收注射在110cm处的标记硝态氮;不施氮的传统及优化灌溉、施氮的传统及优化灌溉对深层标记氮的吸收量分别为336.7、900.3、497.4和657.1mg·m-2,利用率分别是8.4%、22.4%、12.4%和16.3%,适当的水氮胁迫有利于小麦对土壤剖面深层标记硝态氮的吸收利用。4个处理80—150cm土层根长密度占总根长密度(0—150cm)的24.4%、32.3%、26.4%和28.2%,氮素不足优化灌溉有利于小麦中下层根系发育。【结论】耕层氮素养分不足及水分适度胁迫促进小麦中下层根系发育,提高小麦对土壤深层硝态氮的利用。

氮素形态对菠菜硝酸盐及草酸含量的影响

采用水培试验,研究了不同铵硝配比对菠菜体内硝酸盐和各形态草酸含量及分布的影响。结果表明,生物量随供铵比例的增加先显著升高,后显著下降,在铵硝比为25/75和50/50时具有最高生物量。各器官的硝酸盐含量随着供铵比例的升高而显著下降,叶片的草酸总量和可溶态草酸随营养液中铵态氮比例的升高显著降低,而叶柄和侧根的草酸含量在铵硝比为50/50时最低,主根的草酸含量也随铵态氮比例的增加而下降。草酸在菠菜各器官的含量为叶片>主根>叶柄>侧根,并且叶片含量要远远高于其它器官。菠菜体内的草酸以可溶态为主,除在单独供铵处理的叶片中仅占总草酸含量的38%以外,其它处理的均占草酸总量的69%以上。可见,调节营养液中铵硝比例可以调控菠菜体内各形态的草酸含量。铵硝比为25/75和50/50时不仅有利于菠菜生长,而且可降低菠菜体内的可溶态草酸和草酸总量。

粒径对冻融过程中加氮灌溉土壤N_2O排放的影响

通过室内模拟的方法,研究了冻融过程潮土两种粒径(1cm和0.25mm)在加氮灌溉条件下N2O的排放通量,并且分析比较了3种氮素形态(铵态氮、硝态氮和酰胺态氮)和3种浓度(40、200和800mg/L)对土壤N2O的排放通量的影响。结果表明:冻结前,除硝态氮浓度在大于200mg/L时,细土N2O排放通量小于粗粒径土壤,其他氮素形态和浓度得到相反结果;冻结过程细土达到N2O稳定排放通量的时间要早于粗粒径土壤;融化后细土比粗粒径土壤早出现N2O排放峰,并且该峰值总体比粗粒径土壤小;随氮素浓度增加,粗粒径土壤3种氮素形态平均N2O累积排放量分别比细粒径土壤多45.46%、7.81%和46.87%。建议土壤在加氮灌溉时应尽量避免施加硝态氮肥,铵态氮肥的施用应尽量考虑降低浓度,并建议在灌溉越冬水且土壤冻结后耙碎大土块以减少N2O排放。