不同氮硫浓度及氮硫比对硫酸盐还原厌氧氨氧化脱氮效果的影响

该研究在硫酸盐还原厌氧氨氧化（Sulfate-Reducing Anaerobic Ammonium Oxidation,SRAO）脱氮工艺的基础上,探究了SO42-浓度在100 mg/L的条件下,控制NH4+的投加量在不同N/S（NH4+-N/SO42-）浓度比下ASBR（Anaerobic Sequencing Batch Reactor）反应器的运行效果及其脱氮性能。N/S从1.0增大到3.0时,ASBR中氨氮的平均去除率从78.5%增加到94.4%,但体系内SAD（Sulfur Autotrophic Denitrification）菌的丰度及活性未受到明显抑制,SRAO作用和ANAMMOX（Anaerobic Ammonia Oxidation）作用始终是ASBR脱氮的主要途径。当N/S的浓度比由3.0增至4.0时,ASBR中氨氮的平均去除率由94.4%下降为69.2%。这表明随着N/S的增大,体系内ANAMMOX菌和SRAO菌活性的降低,抑制了体系脱氮性能。这时SAD菌的丰度及活性略有增加。硫的去除率随N/S比的变化趋势和总氮的去除规律类似,在N/S=3.0时达到最大74.2%。结合高通量测序结果,说明不同N/S下的脱氮微生物优势菌群会不断变化,改变体系脱氮除硫性能。     

高等植物GS/GOGAT循环研究进展

高等植物体内 95%以上的NH4+通过GS/GOGAT(谷氨酰胺合成酶 /谷氨酸合成酶 )循环同化。GS、GOGAT在植物叶片、根瘤以及根中均有分布 ,但在不同器官中GS/GOGAT循环的作用不尽相同。在绿色组织中 ,GS/GOGAT循环的主要作用是同化光呼吸产生的NH4+以及硝酸盐在叶中还原产生的NH4+,在根瘤中则主要同化根瘤菌固N产生的NH4+,而在根中则是同化吸收到体内的NH4+以及硝酸盐被吸收后在根中还原产生的NH4+。迄今有关植物GS/GOGAT循环的研究还不太深入 ,但是随着基因工程技术、免疫组织化学技术以及现代植物生理学技术的发展 ,GS/GOGAT循环研究展示广阔前景。对该循环及其调控机制的进一步了解 ,可为合理利用氮肥、提高植物N的利用率提供理论依据。本文综述了近年来对GS/GOGAT循环的研究进展情况     

外源氮添加对湿地土壤N_2O排放量的影响

为搞清湿地土壤驱动N2O排放的关键氮源类型,有效减少湿地N2O的排放,本文通过室内控制温湿度,用气相色谱法分析不同外源氮素对湿地N2O排放的影响。结果表明:外加氮源组总是高于对照组N2O排放量(4.4 mg·m-3)。在设定的剂量范围内,单独添加尿素或尿素与硝酸铵1∶1配合时N2O排放量呈现先增后减的单峰分布趋势,峰值分别为10.6 mg·m-3和229.0 mg·m-3;单独添加硝酸铵时N2O排放量(32.6~111.0 mg·m-3)随着氮素添加量增加呈现持续上升趋势。单独添加尿素或硝酸铵、尿素与硝酸铵1∶1配合均促进N2O的排放,但硝酸铵尿素混合添加对N2O排放量的贡献单独添加硝酸铵单独添加尿素。这为预测内蒙古高原区农牧交错带湿地氮素输入可能带来的温室效应和有效减排提供科学依据。     

外源生物质炭对土壤中铵态氮素滞留效应的影响

以生物质炭和黄棕壤为研究材料,通过阳离子交换量测定、铵态氮等温吸附实验以及模拟土柱淋溶,研究生物质炭对土壤铵态氮素滞留效应的影响。发现生物质炭以1%、3%和5%添加后,土壤CEC值分别增加9.4%、14.7%和19.7%,铵态氮素淋失量分别减少22%、39%和47%,氮素滞留量分别增加15%、5%和14%;同时影响氮素在土层中的分布,其中加生物质炭土壤的氮素集中在土柱上部5～7cm处,而不加生物质炭土壤集中在中部偏下9～11cm处。结果表明,生物质炭能够提高土壤对铵态氮素的吸附能力,显著降低土壤铵态氮素养分的淋失。     

土壤中双氰胺降解及与降解菌的关系

采用灭菌土培、非灭菌土培、田间蔬菜种植、添加外源降解菌土培试验研究了土壤中双氰胺（DCD）降解及与降解菌的关系。结果显示,不论是单施DCD、尿素配施DCD,还是碳酸氢铵配施DCD的土壤,灭菌处理的土壤中DCD半衰期分别比不灭菌处理的长13.56、5.79、14.51d。降解菌生长期间,降解菌总量（x）与DCD降解呈显著正相关,拟合的线性方程为y=3.1841x-2.5452,r=0.9752。外源DCD降解真菌可在灭菌土壤中定殖并有效降解DCD,培养15d后,U＋DCD＋DCD降解菌处理土壤中DCD降解真菌的数量增加至36.40×105cfu,且DCD含量极显著降低。这些结果表明土壤中DCD降解与降解菌关系极为密切,添加外源真菌加速了土壤中DCD降解。     

Earthworm biomass and population structure are negatively associated with changes in organic residue nitrogen concentration during vermicomposting

Vermicomposting is an efficient and environmentally friendly technology to dispose of agricultural organic residues. The efficiency of organic residue decomposition during vermicomposting is directly affected by the biomass and population structure of earthworms. In this study, we investigated how the earthworm biomass and population structure responded to changes in the physicochemical properties of six types of organic residue (cattle dung, herbal waste, rice straw, soybean straw, garden waste, and tea residues) during vermicomposting. Each type of organic residues was placed in a pot with earthworms Eisenia fetida, and the physicochemical properties of the organic residues and earthworm growth dynamics were recorded at 0, 30, 60, and 90 d of vermicomposting. The biomass and population structure of earthworms were stable or increased in rice straw, garden waste, and cattle dung within 60 d of vermicomposting, whereas in tea residues and herb waste, very little earthworm activity (3 adults and 2 cocoons) was recorded on day 30. Among the physicochemical parameters, the substrate C/N ratio was negatively correlated with earthworm growth dynamics. Decomposing organic residues showed higher NH₄⁺-N and NH₃^--N concentrations but a lower total organic carbon content, which negatively affected earthworm growth and reproduction. We recommend that chemical properties of vermicomposting systems should be monitored regularly. At the threshold levels of decomposing organic residue NH₄⁺-N and NH₃^--N concentrations, earthworms should be removed and the vermicompost can be harvested. Small- and large-scale farmers thus need to monitor the physicochemical properties of vermicompost to sustain active earthworm populations.     

温度对酸性草酸-草酸铵溶液浸提土壤无定形铁的影响

以下蜀黄土为试材,研究温度对酸性草酸-草酸铵缓冲溶液浸提土壤无定形铁的影响。结果表明:随着浸提温度的升高,铁的浸提量明显增加。30℃浸提出的铁约为20℃的1.57倍;而50℃浸提出的铁约为20℃的4.43倍。随温度的升高,浸提后土壤残渣的磁化率迅速降低。20℃浸提后残渣的磁化率值比原样略有减少;30℃浸提后残渣的磁化率约为原样的93.6%;50℃浸提后残渣的磁化率只有原样的65.3%。这说明随着温度的升高,以磁性矿物为代表的结晶态铁也被溶解,浸提出的铁其实已不仅是无定形铁。因此,用酸性草酸铵浸提无定形铁时,严格控制20℃的反应温度十分关键。     

Determination of ammonium n and nitrate n in acid permanganate solution used to absorb ammonia,nitric oxide,and nitrogen dioxide evolved from soils

Abstract

Simple steam distillation methods are described for determination of ammonium N and nitrate N in acid KMnO₄ solution used to absorb NH₃, NO and NO₂ evolved from soils. They involve use of MgO for distillation of ammonia and of FeSO₄, Ag₂SO₄, and MgO for reduction of nitrate to ammonia. The methods are rapid and precise, and they permit nitrogen‐15 analysis of NH₃‐N and (NO + NO₂)‐N evolved from soils.     

Clay mineralogical and ammonium fixation characteristics of some tropical upland rice soils

Abstract

In view of the agronomic and economic significance of NH₄ fixation in soils, an attempt has been made to relate this to the most reactive mineral constituents of soils ‐ the clay minerals, under the temperature‐moisture regimes normal to tropical upland rice soils. Laboratory fixation study was done with NH₄, concentrations similar to those common in soils upon N fertilization, and under alternate wetting and drying at ambient temperatures rather than at 100°C as in many published studies.

Results of the investigation show that soil clays with dominant vermiculite and montmorillonite fix the greatest proportion of applied NH₄ (94 and 91%), followed by beidellite (72%) and x‐ray amorphous (45–64%) clays. Fixation is negligible (10%) in the clay with mineral suite consisting of hydrous mica, halloysite, and chlorite. Crystallinity of minerals seems to influence NH₄ fixation appreciably.     

Nitrogen effect on yield and kernel protein content of sweet corn grown on sandy soils

Abstract

Early spring application of N to Iowa sandy, leachable soils results in reduced sweet corn yields and kernel protein content. Normally, split N applications are used to coincide with crop N demand. Our objectives were to determine if nitrapyrin, a nitrification inhibitor, applied with urea would provide high yields and kernel protein levels when applied at planting.

Nitrogen rate increased yield, ear leaf N concentration, and kernel protein content in 1976 and 1978, with the optimum rate dependent on the year and soil N residual. Urea, with or without nitrapyrin, significantly enhanced yield 13%, early leaf N concentration 17%, and kernel protein content 9% as compared with Ca(NO₃)₂ for both years. High leaching loss of NO₃‐N occurred with the Ca(NO₃)₂ source as compared with urea alone. Kernel protein concentration correlated well with ear leaf N concentration (r = .74) and yield (r = .61). Ear leaf K content was not affected by N rate or source, but Ca(NO₃)₂ enhanced uptake of Ca and Mg as compared with the urea sources. Urea, with nitrapyrin, decreased leaf Mg content in 1978, but not in 1976, as compared with urea alone.