Total soil nitrogen and nitrogen mineralization

Summary The mineralization capacity of 24 different soils was determined from incubation experiments. Relatively rapid mineralization and nitrification was found with soils from cultivated land, and pastures, but soils under natural vegetative covers of conifers and hardwoods were mostly ammonifying. A close relationship could be established between the total nitrogen content of the soil and the amount of mineral nitrogen formed during incubation. Important connections could also be shown between the available nitrogen contents at different times during the incubation period; these suggest that the incubation period can be considerably shortened.     

Changing nitrogen source on the yield and nitrogen content of soybeans

Summary Soybean plants were grown in nutrient culture solutions containing 150 ppm of N either as an equal concentration of NH₄ ⁺ or NO₃ ^–, or all NO₃ ^–. At the R2 stage of growth for some plants, the N form was changed to either all NO₃ ^– or all NH₄ ⁺, but at the same total N concentration as before. Highest seed yield was obtained with all NO₃ ^– over the entire growth period, the poorest when the N form was switched from an equal ratio of NH₄ ⁺ and NO₃ ^– to all NH₄ ⁺ at the R2 stage. Kjeldahl N concentrations in the plant leaves and seed were highest when NH₄ ⁺ was part or all of the N source in the nutrient solution. These results may partially explain why the literature is inconsistent on the effect of added fertilizer N on soybean seed yield, and may pose a problem in using leaf Kjeldahl N concentration to determine plant N sufficiency.     

香蕉苗期氮素亏缺与补偿对植株生长和根系形态的影响

为探究氮素亏缺及亏缺后补偿供氮对蕉苗生长及其根系形态特征的影响,该研究以主要栽培品种基因组类型(AAA型和ABB型)的香蕉品种为材料,通过石英砂基质培养结合氮素亏缺与补偿处理,分析其株高、叶长、叶宽、新增绿叶数、地上部和根系的鲜重和干物质质量、根长和根表面积及根体积等指标的变化。结果表明：(1)亏缺30 d,香蕉苗呈现明显的缺氮表型症状,株高、叶长、叶宽及新增绿叶数均显著降低,根系干物质积累增加,品种Ⅰ、Ⅱ根系干物质分别提高64.71%、87.50%,根冠比增加,总根表面积分别增加4.38%、11.85%,体积分别增加71.78%、66.55%。(2)亏缺68 d,干物质积累受到明显抑制,品种Ⅰ、Ⅱ全株干物质质量降低33.74%、42.04%,根系干物质质量与常规处理无显著差异,根系形态参数变化趋势与轻度亏缺一致。(3)亏缺后补偿供氮,缺氮症状消失,植株生长指标恢复正常水平;品种Ⅰ、Ⅱ根系干物质质量显著增加51.22%、52.38%,根冠比显著高于常规处理,根系趋向正常形态生长,并且总根体积分别增加61.80%、45.92%;轻度氮素亏缺后适时补偿供氮,缺氮蕉苗可恢复正常生长,根系干物...     

追施氮肥当年与翌年对桉树生长及各部位氮贮量的影响

采用田间定位试验方法,研究了追施氮肥当年与翌年对桉树各部位生物量和氮贮量的影响。结果表明:与对照相比,追施氮肥翌年桉树生物量增加幅度显著高于当年,说明氮肥对于提高桉树生物量具有一定累积作用,追肥的增产效果明显;追施氮肥也使全树氮贮量在2007年与2008年分别提高30.2%和73.5%;与2007年相比,2008年对照处理桉树生物量增加35.9%,追施氮肥处理生物量提高1倍以上,而对照处理树木体内氮贮量降低13.1%,追氮处理提高15.7%;这主要是由于3龄桉树树叶生物量的明显降低,对照与追施氮肥处理树叶中氮贮量分别降低46.5%和36.9%,其也是桉树中氮贮量降低最显著的部位。     

Carbon and nitrogen stoichiometry and nitrogen cycling rates in streams

Stoichiometric analyses can be used to investigate the linkages between N and C cycles and how these linkages influence biogeochemistry at many scales, from components of individual ecosystems up to the biosphere. N-specific NH₄⁺ uptake rates were measured in eight streams using short-term ¹⁵N tracer additions, and C to N ratios (C:N) were determined from living and non-living organic matter collected from ten streams. These data were also compared to previously published data compiled from studies of lakes, ponds, wetlands, forests, and tundra. There was a significant negative relationship between C:N and N-specific uptake rate; C:N could account for 41% of the variance in N-specific uptake rate across all streams, and the relationship held in five of eight streams. Most of the variation in N-specific uptake rate was contributed by detrital and primary producer compartments with large values of C:N and small values for N-specific uptake rate. In streams, particulate materials are not as likely to move downstream as dissolved N, so if N is cycling in a particulate compartment, N retention is likely to be greater. Together, these data suggest that N retention may depend in part on C:N of living and non-living organic matter in streams. Factors that alter C:N of stream ecosystem compartments, such as removal of riparian vegetation or N fertilization, may influence the amount of retention attributed to these ecosystem compartments by causing shifts in stoichiometry. Our analysis suggests that C:N of ecosystem compartments can be used to link N-cycling models across streams.     

Uptake of fertilizer nitrogen and soil nitrogen by rice using15N-labelled nitrogen fertilizer

Data from five field experiments using labelled nitrogen fertilizer were used to determine the relative effects of soil nitrogen and fertilizer nitrogen on rice yield. Yield of grain was closely correlated with total aboveground nitrogen uptake (soil+fertilizer), less closely correlated with soil nitrogen uptake and not significantly correlated with fertilizer nitrogen uptake. When yield increase rather than yield was correlated with fertilizer nitrogen uptake, the correlation coefficient was statistically significant.Contribution from the Laboratory for Flooded Soils and Sediments, Agronomy Dept., Louisiana Agri. Exper. Sta., Louisiana State Univ., Baton Rouge, LA 70803, and Univ. of Florida, Agricultural Research and Education Center, Sanford, FL 32771.     

氮肥形态对冬小麦根际土壤氮素生理群活性及无机氮含量的影响

采用大田盆栽方法研究了硝态氮肥、铵态氮肥、酰胺态氮肥3种氮肥形态对冬小麦品种豫麦50生育中后期(拔节期、开花期、花后14 d、花后28 d)根际土壤氮转化相关微生物活性、酶活性和根际土壤NH+4离子、NO-3离子含量的影响。结果表明:随着生育期的推进,除脲酶外,氨化细菌、硝化细菌、亚硝化细菌、反硝化细菌和蛋白酶活性变化的均为"倒V"型变化特征,以花后14 d活性最强;而脲酶活性在拔节期最强,并且其活性远大于其它微生物及酶。氮肥形态对根际土壤氮素生理群及无机氮的影响不同。酰胺态氮肥促进了根际氨化细菌、反硝化细菌、脲酶、蛋白酶的活性,而硝化细菌、亚硝化细菌在硝态氮肥条件下活性较强。除拔节期外,土壤中NH+4离子在铵态氮肥处理下含量较高,NO-3离子在酰氨态氮肥处理下含量较高。因此,酰胺态氮能够促进小麦根际土壤有机氮的分解,硝态氮肥可以促进土壤中氨的转化,以利于小麦根系的吸收与利用。氮肥形态主要是通过影响土壤中氮素生理类群及酶的活性,从而影响土壤中无机氮的含量。     

Modelling and measuring the effect of nitrogen catch crops on the nitrogen supply for succeeding crops

Nitrogen catch crops are grown to absorb nitrogen from the rooting zone during autumn and winter. The uptake of N (N_upt) from the soil inorganic N pool (N_min) to a pool of catch crop nitrogen, will protect the nitrogen against leaching. After incorporation, a fraction (m) of the catch crop nitrogen is mineralized and becomes available again. However, not all available nitrogen present in the soil in the autumn is lost by leaching during winter. A fraction (r) of the nitrogen absorbed by the catch crop would, without a catch crop, have been retained within the rooting zone. The first year nitrogen beneficial effect (N_eff) of a catch crop may then be expressed b N _eff = m*N _upt - r* N _upt The soil-plant simulation model DAISY was evaluated for its ability to simulate the effects of catch crops on spring N_min and N_eff. Based on incubation studies, parameter values were assigned to a number of catch crop materials, and these parameter values were then used to simulate spring Nmin. The model was able to predict much of the vairiation in the measured spring Nmin (r² = 0.48***) and there was good agreement between the measured and the simulated effect of winter precipitation on spring N_min and Neff.Scenarios including variable soil and climate conditions, and variable root depth of the succeeding crop were simulated. It is illustrated that the effect of catch crops on nitrogen availability for the succeeding crop depends strongly on the rooting depth of the succeeding crop. If the succeeding crop is deep rooted and the leaching intensity is low, there is a high risk that a catch crop will have a negative effect on nitrogen availability. The simulations showed that the strategy for the growing of catch crops should be adapted to the actual situation, especially to the expected leaching intensity and to the rooting depth of the succeeding crop.     

The contribution of associative and symbiotic nitrogen fixation to the nitrogen nutrition of non-legumes

During the past 10 years estimates of N₂ fixation associated with sugar cane, forage grasses, cereals and actinorhizal plants grown in soil with and without addition of inoculum have been obtained using the ¹⁵N isotope dilution technique. These experiments are reviewed in this paper with the aim of determining the proportional and absolute contribution of N₂ fixation to the N nutrition of non-legumes, and its role as a source of N in agriculture. The review also identifies deficiencies in both the totality of data which are currently available and the experimental approaches used to quantify N₂ fixation associated with non-legumes.Field data indicate that associative N₂ fixation can potentially contribute agronomically-significant amounts of N (>30–40 kg N ha^-1 y^-1) to the N nutrition of plants of importance in tropical agriculture, including sugar cane (Saccharum sp.) and forage grasses (Panicum maximum, Brachiaria sp. and Leptochloa fusca) when grown in uninoculated, N-deficient soils. Marked variations in proportions of plant N derived from the atmosphere have been measured between species or cultivars within species.Limited pot-culture data indicate that rice can benefit naturally from associative N₂ fixation, and that inoculation responses due to N₂ fixation can occur. Wheat can also respond to inoculation but responses do not appear to be due to associative N₂ fixation. ¹⁵N dilution studies confirm that substantial amounts of N₂ can be fixed by actinorhizal plants.     

The nitrogen requirements and dietary nitrogen utilization for the gecarcinid land crab Gecarcoidea natalis

The nitrogen requirements for tissue maintenance, moulting, and oogenesis were determined experimentally for the herbivorous land crab Gecarcoidea natalis. The maintenance nitrogen requirements for intermoult animals was very low (4.83+/-1.68 mmol N kg-1 dry body wt d-1), but during oogenesis the total requirement was much higher (8. 6 mmol N kg-1 dry body wt d-1). Gecarcoidea natalis could potentially assimilate enough nitrogen from rain forest leaf litter or leaves of Ficus or Erythrina to satisfy not only the maintenance nitrogen requirements but the observed rate of incorporation of nitrogen into the ovaries during oogenesis. The ovaries developed slowly over a period of 2 mo (mid-July to late September) and had a final nitrogen content of 359+/-15.9 (n=18) mmol kg-1 dry body wt. This was equivalent to 9.3%+/-0.4% of the total body nitrogen. A substantial nitrogen debt was incurred during ecdysis (658+/-126 mmol kg-1 dry body wt). This nitrogen debt could be satisfied slowly, from leaf litter, over a period of 1-3 mo. After ecdysis, the majority of the nitrogen and urate within the animal prior to moulting was retained within the soft crab (85.0%+/-1.2% total nitrogen, 82.0%+/-1.2% nonurate nitrogen and 99.56% urate), while only a minority was lost with the exuviae (18.0%+/-1.2% total nitrogen, 14.7%+/-1.2% nonurate nitrogen, and 0.4%+/-0.4% urate). The urate deposits in G. natalis were not mobilized as a source of nitrogen in animals maintained on a nitrogen-free diet.     

The effects of nitrogen application on growth and nitrogen distribution within the potato canopy

The effect of applying nitrogen (N) fertiliser on the growth and distribution of N within the potato canopy was studied in 1983 and 1984. In both years N was applied either in excess of that required to produce maximum tuber yields, or not at all. The large application of N changed the pattern of canopy growth - stimulating growth of leaves at the top of the stem, particularly lateral branches, for longer during the season, and accelerating the death of (shaded) leaves at the base of the canopy. The pattern of canopy senescence was, therefore, changed from a synchronous to a progressive type. Application of nitrogen fertiliser at supra-optimal rates increased the N contents of leaves, stems and tubers. The extra N in the leaves of these plants was present as reduced N in all leaf positions, and as nitrate (NO^-₃) in the lowermost leaves. In addition, substantial quantities of NO^-₃ were also stored in the stems. Part of this extra N in the canopy was redistributed during subsequent growth, especially to the lateral branches as crop N uptake slowed towards the end of the season. In addition, substantial quantities of N were also potentially available for redistribution to the growing tubers. There was little redistribution of N from the leaves of N-deficient plants. It is suggested that redistribution of N in the canopy of N-replete plants allowed the growth of lateral branches towards the end of the season, thereby maintaining photosynthetically active leaves for longer than N-deficient plants.     

不同供氮量对二月兰产量、土壤无机氮残留及氮平衡的影响

研究华北冬绿肥二月兰对不同供氮水平的响应特征,确定实现绿肥高产高效的土壤适宜供氮量,可为华北集约化农田最大化发挥绿肥生态效应和优化春玉米/冬绿肥轮作体系氮素管理提供理论依据和技术参考.选取多年不施肥试验地设置供氮梯度试验,研究了不同供氮水平对冬绿肥二月兰翻压前地上部生物量累积、氮素吸收、土壤无机氮残留和冬绿肥季土壤氮素平衡的影响.结果表明: 在土壤无机氮含量较低(0～90 cm土层15 kg·hm^-2)条件下,施氮显著提高二月兰生物量和吸氮量.其中,施氮90 kg·hm^-2处理表现最高,绿肥生物量(干质量)和吸氮量分别为2031.0和42.0 kg·hm^-2;土壤无机氮残留量随施氮量增加而增加,且在施氮量高于60 kg·hm^-2后呈现快速增加趋势;随施氮量增加二月兰生长季的表观氮平衡表现出由亏缺到盈余的变化特征,在施氮量为60～90 kg·hm^-2条件下氮收支基本平衡.土壤供氮量(绿肥播前0～90 cm土壤无机氮含量与施氮量之和)与二月兰生物量、吸氮量和绿肥翻压前土壤无机氮含量的关系可以分别用二次、线性加平台和指数方程进行模拟,依据模型计算二月兰生物量最高值(2010 kg·hm^-2)时的播前土壤供氮量和绿肥翻压前土壤无机氮残留量分别是136和78 kg·hm^-2;而在二月兰吸氮量最高值40 kg·hm^-2时,二月兰生物量为1919 kg·hm^-2,相当于最高生物量的95%,绿肥翻压前土壤残留无机氮降低至57 kg·hm^-2,与之对应的播前土壤供氮量为105 kg·hm^-2,该值与目前华北地区优化施氮下玉米收获后土壤残留无机氮推荐含量(100 kg·hm^-2)基本相当.综合考虑绿肥的农学和环境效应,春玉米/冬绿肥轮作体系中二月兰播前土壤供氮量应控制在100～105 kg·hm^-2.     

Enzymology and ecology of the nitrogen cycle

The nitrogen cycle describes the processes through which nitrogen is converted between its various chemical forms. These transformations involve both biological and abiotic redox processes. The principal processes involved in the nitrogen cycle are nitrogen fixation, nitrification, nitrate assimilation, respiratory reduction of nitrate to ammonia, anaerobic ammonia oxidation (anammox) and denitrification. All of these are carried out by micro-organisms, including bacteria, archaea and some specialized fungi. In the present article, we provide a brief introduction to both the biochemical and ecological aspects of these processes and consider how human activity over the last 100?years has changed the historic balance of the global nitrogen cycle.     

浮床黑麦草对城市生活污水氮循环细菌繁衍和脱氮效果的影响

通过设施大棚内容积为1.5m3的人工模拟池试验,研究了浮床黑麦草对模拟城市生活污水氮循环细菌繁衍和脱氮效果的影响。通过研究,阐明浮床植物去除污染水体氮素的可能途径。研究结果表明:浮床黑麦草对模拟城市生活污水总氮和氨氮的去除效果分别达到了31.6%和43.0%;浮床黑麦草根际和根系正下方是各类氮循环细菌生长的最佳区域;浮床黑麦草处理有效地提高了系统氮循环细菌的数量,16d的试验结束时细菌总数(A,单位为CFU.mL-1)达到最大值,其lg(A/(CFU.mL-1))增加至8.82,各类氮循环细菌比对照高3-5个数量级;同时,浮床黑麦草处理显著提高了氮循环细菌的群落多样性,系统内氨化菌、硝化菌、亚硝化菌和反硝化菌共存;明确了浮床黑麦草的吸收同化和氮循环细菌的生物脱氮是浮床黑麦草净化水质的两个重要途径。     

The effect of nitrogen fertilization on the release of soil nitrogen

Summary The effect of fertilizer nitrogen on the available amount of soil nitrogen was investigated in a greenhouse experiment. To 9 different soils, 0, 50, 100 and 200 kg N/ha were applied, resp., as (N¹⁵H₄)₂SO₄ with an atom excess N-15 of 1%.No priming effect could be found for any of the treatments. The available amount of soil N, expressed as A_N value, was not affected by rate of N-fertilizer application.     

Atmospheric nitrogen deposition has caused nitrogen enrichment and eutrophication of lakes in the northern hemisphere

We compiled chemical data and phytoplankton biomass (PB) data (chlorophyll a ) from unproductive lakes in 42 different regions in Europe and North America, and compared these data to inorganic nitrogen (N) deposition over these regions. We demonstrate that increased deposition of inorganic N over large areas of Europe and North America has caused elevated concentrations of inorganic N in lakes. In addition, the unproductive lakes in high N deposition areas had clearly higher PB relative to the total phosphorus (P) concentrations illustrating that the elevated inorganic N concentrations has resulted in eutrophication and increased biomass of phytoplankton. The eutrophication caused by inorganic N deposition indicates that PB yield in a majority of lakes in the northern hemisphere is (was) limited by N in their natural state. We, therefore, suggest that P limitation largely concerns lakes where the balance between N and P has been changed because of increased anthropogenic input of N.