棉花蕾花铃生物量、氮累积特征及临界氮浓度稀释模型

在大田栽培条件下，于河南安阳（黄河流域黄淮棉区）和江苏南京（长江流域下游棉区）设置了棉花氮素水平试验，对不同氮素水平条件下棉花蕾花铃的生物量、氮素累积及氮浓度的动态变化进行分析，并依据Justes的临界氮浓度稀释模型确定方法，研究棉花蕾花铃临界氮浓度稀释模型。结果表明：棉花蕾花铃的生物量增长和氮吸收累积均受氮素水平的影响，其动态变化符合S型曲线，氮累积的快速起始时间较生物量早1～5d；氮浓度过高或过低均不利于产量形成，蕾花铃等器官存在氮奢侈消费现象；氮浓度随施氮量的增加而升高、随生育进程的推移而降低，其生物量累积量与氮浓度间符合幂函数关系，两试点蕾花铃氮稀释曲线模型形式相同，但模型参数a不同，不同生态区存在独立的临界氮稀释曲线模型。由于临界稀释模型具有明确的生物学意义，可以作为定量诊断蕾花铃氮营养动态变化的指标之一。     

氮素水平对初花后棉株生物量、氮素累积特征及氮素利用率动态变化的影响

在大田栽培条件下,分别在长江流域下游棉区(江苏南京)和黄河流域黄淮棉区(河南安阳)设置棉花氮素水平试验,定量研究氮素水平对花后棉株生物量、氮素累积特征及氮素累积利用率动态变化的影响,结果表明:棉株总生物量和氮素累积量随花后棉株生育进程的动态变化符合S型曲线,安阳、南京试点分别以360kg.hm-2、240kg.hm-2氮素水平的总生物量、氮素累积最多,其动态累积模型的特征参数值最为协调,皮棉产量最高。因此,可以通过改变施肥量来调节初花后棉株生长特征值,从而获得高产。棉株氮素累积利用率随初花后棉花生育进程的推进,呈现为不规则的S型曲线变化趋势,计算两试点的氮素累积利用率、瞬时利用率,安阳试点以360 kg.hm-2的施氮水平为最优,南京以240 kg.hm-2最高;施肥过多不仅利用率低,而且易造成营养器官比例加大,棉株虽可获得较大的干物质和氮素累积,但不能适时向生殖器官转移,皮棉产量降低。     

施氮量和种植密度对东北特早熟棉区棉花生物量和氮素累积的影响

以辽棉19号和美棉33B为材料,于2008年在东北特早熟棉区设置不同的棉花种植密度(每公顷75000、97500、120000株)和施氮量(0、240、480 kg·hm-2),研究了施氮量和种植密度对东北特早熟棉区棉花生物量、氮素累积特征和氮素累积利用率的影响.结果表明:两个品种的棉花生物量和氮素累积量随棉花生育进程的动态变化均符合Logistic模型;种植密度和施氮量显著影响棉花氮素累积动态特征以及棉花产量和品质;氮素的快速累积起始日较生物量早13 d左右.在种植密度为每公顷97500株、240 kg·hm-2施氮量处理下,两个品种棉花的生物量和氮素动态累积模型的特征参数最为协调,皮棉产量最高,纤维品质最优,氮素利用效率最高.在东北特早熟棉区,较早的生物量和氮素快速累积及较高的累积速率有利于棉花较高产量的形成.     

施氮量和种植密度对东北特早熟棉区棉铃生物量和氮素累积的影响

以辽棉19号和美棉33B为材料,研究了不同施氮量(0、240、480 kg·hm-2)和不同种植密度(75000、97500、120000 plants·hm-2)对东北特早熟棉区棉花棉铃生物量和氮素累积特征的影响.结果表明:棉花单铃、棉籽和纤维的生物量及其氮素累积随棉花生育进程的动态变化均符合“S”型曲线,种植密度和施氮量可以显著影响棉铃各部分生物量和氮素累积的动态特征,以及棉花产量与品质;在施氮量240 kg· hm-2和种植密度97500 plants·hm-2处理下,单铃、棉籽和纤维的生物量均达到最大,生物量和氮素累积的快速累积起始时间和终止时间较早但持续时间较短,生物量快速累积速率最大,生物量和氮素在铃壳中的分配系数最低,在棉籽和纤维中分配系数最高.     

施氮量对花铃期棉花果枝生物量累积时空变异特征的影响

试验在黄河流域黄淮棉区的河南安阳和长江流域下游棉区的江苏南京棉花大田进行， 氮素设0（N₀）、120（N₁）、240（N₂）、360（N₃）、480（N₄） kg·hm^-2 5个水平，定量分析了不同施氮量对美棉33B花铃期棉花果枝生物量累积时空变异特征的影响.结果表明： 不同施氮量下，两试验点棉株不同果枝部位营养器官、生殖器官、生物量累积时间变异特征均表现为Logistic曲线，空间变异特征存在明显差异.安阳点360 kg·hm^-2施氮量、南京点240 kg·hm^-2施氮量处理具有快速增长期起始时间早、持续时间短、最大速率大等特征，说明该施氮量水平有利于棉花生物量的快速累积，以形成较高的产量与品质；而施氮量过多或不足均不利于棉株不同果枝部位生物量的累积.可以通过不同的施氮量来调节棉株不同果枝部位快速生长期的生长特征值，以提高棉花的产量和品质.     

棉花临界需氮量动态定量模型

在大田栽培条件下,于江苏南京和河南安阳两个生态区设置棉花氮素水平试验,基于作物临界氮浓度稀释模型和干物质动态累积模型,建立了棉花花后动态临界氮吸收速率、临界氮需求量的定量化模型.结果表明,两生态区的临界最大氮吸收速率均出现在花后42 d,分别为5.3和4.4 kg·hm^-2·d^-1,临界快速氮累积期分别在花后的23～59 d和23～61 d,安阳的最大临界日需氮量明显大于南京.根据模型得到：安阳生态区适宜施氮量在240～360 kg·hm^-2 之间,且360 kg·hm^-2 条件下其氮累积接近临界需求,南京生态区240 kg·hm^-2施氮量的氮累积与临界值相近.两区域基肥施用量分别占总施肥量的26%和27%,且适宜的追肥时间应在花后22 d左右.由于模型的建立是基于不同氮处理试验,有合理可靠的生理依据,为定量确定不同气候区域的动态施肥量提供了理论依据.     

施氮量对麦后直播棉氮素吸收利用的影响

以早熟棉中棉所50为材料进行麦后直播棉花试验,研究施氮量(0、60、120、150、180、240kg N·hm~(-2))对棉株氮素吸收、利用和分配的影响.结果表明:增施氮肥提高了麦后直播棉不同生育阶段的氮吸收量,以盛花到见絮期的氮积累增量最大,并且改变了不同生育期间氮吸收比例,使棉花出苗到盛花期的氮吸收比例降低,盛花到吐絮期的氮吸收比例升高;增施氮肥还降低了生育后期中上部位果枝氮浓度的下降速率.麦后直播棉氮素和生物量累积以中下部果枝为主,在150-180 kg N·hm~(-2)施氮量下棉花产量、氮肥表观利用率、各果枝部位干物质和氮在生殖器官中的分配比例较高,氮浓度和氮累积量动态特征参数比较协调.高于180kg N·hm~(-2)的施氮量导致棉花中部和下部果枝生殖器官生物量和氮素累积量、产量增幅和氮肥利用率降低,而低于150 kg N·hm~(-2)施氮量降低棉花整株干物质和氮经济系数,不利于高产形成.综合分析,150~180kg N·hm~(-2)施氮量可作为长江流域下游棉区麦后直播棉的推荐施氮量.     

水氮运筹对棉花花后生物量和氮素利用率的影响

在池栽和大田条件下,以‘美棉33B’为材料,研究不同水分(自然降水、自然降水 灌水)和氮素(0、240、480kgN/hm2)运筹下棉花花后生物量和养分累积及氮素利用率动态变化特征。结果表明:施氮使棉花(整株、营养器官、生殖器官)生物量和养分快速累积期持续时间缩短、最大累积速率增大且出现时间提前、累积量及皮棉产量增加。灌水使240 kgN/hm2处理棉花(整株、营养器官、生殖器官)生物量和养分快速累积期持续时间缩短、最大累积速率出现时间提前、最大累积速率和累积量增大、氮素累积利用率和产量提高;而使480 kgN/hm2处理棉花营养器官生物量和养分快速累积期持续时间延长、最大累积速率出现时间推迟、生物量和养分最大累积速率及累积量增大、氮素累积利用率提高,而生殖器官相应指标呈降低趋势;灌水对不施氮处理棉花生物量和养分累积各项特征参数影响较小。营养器官生物量和氮磷钾最大累积速率出现时间较生殖器官早23 d左右,而快速累积期持续时间长于生殖器官11 d左右。研究发现,水分和氮素运筹可通过影响棉花生物量和养分累积的动态特征参数来影响棉花生长,进而影响最终产量品质形成;在本实验条件下,以灌水的240 kgN/hm2处理棉花的生长特征参数最为协调,皮棉产量和氮素利用率最高,品质较优。     

棉花花铃期短期干旱下氮素对干物质及氮素累积分配的影响

通过盆栽试验进行水分(正常灌水和干旱后复水)和施氮处理(0、240、480kgN·hm-2),研究花铃期短期干旱再复水后氮素对棉花各器官干物质重、氮素累积与分配及产量与品质的影响.结果表明:花铃期土壤干旱显著降低了棉株各器官的干物质重与氮素累积量,而增大了棉株各器官的氮素含量,同时亦降低了棉株干物质与氮素在叶片中的分配指数,但提高了在根系的分配指数,从而增大了根冠比;增施氮肥可以提高干旱条件下棉株的干物质重与氮素累积量,但亦增大水分胁迫指数.复水对干旱处理棉株生长具有明显的补偿效应,尤其是根系的干物质重与氮素累积量显著高于相应正常灌水处理,且增施氮肥可以提高棉株的补偿效应.花铃期干旱结束时与复水后第10天,干旱处理棉株均以240kgN·hm-2水平下的生殖器官干物质重与分配指数最高,而根冠比最小,地上部与地下部生长最为协调,最终籽棉产量最高、纤维品质最优;而施氮不足(0kgN·hm-2)或过量(480kgN·hm-2)均不利于棉花产量的提高与纤维品质的改善.     

减量施氮与大豆间作对蔗田氮平衡的影响

通过2010—2013年的大田试验,探讨了2个施氮水平(300和525 kg·hm-2)和3种种植模式(甘蔗、大豆单作及甘蔗-大豆1∶2间作)对蔗田大豆固氮、甘蔗和大豆氮素累积及氨挥发和氮淋溶的影响.结果表明:与大豆单作相比,甘蔗-大豆间作的大豆固氮效率下降,但不同施氮水平间作模式之间无显著差异.不同施氮水平和种植模式对甘蔗、大豆氮素累积无显著影响.减量施氮水平下氨挥发量低于常规施氮处理,不同施氮水平和种植模式对氮淋溶量无显著影响.除2011年甘蔗单作减量施氮水平下出现蔗田氮素亏缺(-66.22 kg·hm-2)外,其余不同年份不同种植模式下氮素都处于盈余状态(73.10~400.03 kg·hm-2),施氮水平显著影响了蔗田的氮素盈亏,且常规施氮水平下氮素盈余量显著高于减量施氮处理,过高的氮素盈余增加了氮素污染农田环境的风险.从培肥地力、降低氮素污染环境的风险和节约生产成本等方面考虑,减量施氮水平下甘蔗-大豆间作模式具有一定的生态合理性.     

The nitrogen status of Austrian forest ecosystems as influenced by atmospheric deposition,biomass harvesting and lateral organomass exchange

Measurements of the deposition rates of atmospheric trace constituents to forest ecosystems in Austria have shown that the deposition of plant utilizable nitrogen compounds is in the range from 12 kg N to more than 30 kg N ha^-1 a^-1. Locally, even higher deposition rates are encountered as a consequence of point sources or special deposition mechanisms such as fog interception, hoar frost formation, and accumulation in snow drifts. In order to place these values into perspective, they are compared with the nitrogen demand of past and present forest land use and with natural processes of nitrogen depletion and accumulation in forest ecosystems. During wind erosion of forest litter, woody material with a wide C/N-ratio remains on the windward side of ridges, while nutrient-rich material with a narrow C/N-ratio is deposited on the leeward side. As a result, total nitrogen storage in the forest soil as well as overall C/N-ratios change dramatically along a transect over a ridge, thus indicating a strong influence of litter C/N ratio on nitrogen retention in the forest soil. A study of nitrogen stores in the soil of beech ecosystems of the same yield class in the Vienna Woods showed a significant correlation of total N-content with base saturation. These results suggest that nitrogen storage capacity of forest soils may be managed by liming and tree species selection. As knowledge is still meagre, a special study on factors which determine nitrogen storage in forest soils is proposed within the FERN-programme.     

Nitrogen yields from undisturbed watersheds in the Americas

Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha^–1 y^–1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r²=0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.     

The impact of humans on the nitrogen cycle,with focus on temperate arable agriculture

The 6 billion people alive today consume about 25 million tonnes of protein nitrogen each year, a requirement that could well increase to 40–45 million tonnes by 2050. Most of them ultimately depend on the Haber-Bosch process to fix the atmospheric N₂ needed to grow at least part of their protein and, over the earth as a whole, this dependency is likely to increase. Humans now fix some 160 million tonnes of nitrogen per year, of which 98 are fixed industrially by the Haber-Bosch process (83 for use as agricultural fertilizer, 15 for industry), 22 during combustion and the rest is fixed during the cultivation of leguminous crops and fodders. These 160 million tonnes have markedly increased the burden of combined nitrogen entering rivers, lakes and shallow seas, as well as increasing the input of NH₃, N₂O, NO and NO₂ to the atmosphere. Nitrogen fertilizers give large economic gains in modern farming systems and under favourable conditions can be used very efficiently. Losses of nitrogen occur from all systems of agriculture, with organic manures being particularly difficult to use efficiently. Although nitrate leaching has received much attention as an economic loss, a cause of eutrophication and a health hazard, gaseous emissions may eventually prove to be the most serious environmentally. Scientists working on the use and fate of nitrogen fertilizers must be careful, clear headed and vigilant in looking for unexpected side effects.     

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg^–1 dry soil)=(N_min×0.672)+(N_inc×0.840)+(N_mom×0.227)–5.12 was found to account for 91% of the variance in available soil N, where N_min=mineral N, N_inc=N mineralized on incubation and N_mom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (N_ao) the closest relationship with other soil characteristics was: N_ao=[N_inc×(1.395–0.0347×CN_mom]+[N_mom×0.1416], where CN_mom=CN ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.     

Yield of nitrogen from minimally disturbed watersheds of the United States

Watersheds of the US Geological Survey's Hydrologic Benchmark Network program were used in estimating annual yield of total nitrogen and nitrogen fractions (ammonium, nitrate, dissolved organic N, particulate N) in relation to amount of runoff, elevation, and watershed area. Only watersheds minimally disturbed with respect to the nitrogen cycle were used in the analysis (mostly natural vegetation cover, no point sources of N, atmospheric deposition of inorganic N < 10 kg ha^–1 y^–1). Statistical analysis of the yields of total nitrogen and nitrogen fractions showed that elevation and watershed area bear no significant relationship to nitrogen yield for these watersheds. The yields of total nitrogen and nitrogen fractions are, however, strongly related to runoff (r ² = 0.91 for total N). Annual yield increases as runoff increases, but at a rate lower than runoff; annual discharge-weighted mean concentrations decline as annual runoff increases. Yields of total nitrogen and most nitrogen fractions bear a relationship to runoff that is nearly indistinguishable from a relationship that was documented previously for minimally disturbed watersheds of the American tropics. Overall, the results suggest strong interlatitudinal convergence of yields and percent fractionation for nitrogen in relation to runoff.     

Nitrogen outputs from fecal and urine deposition of small mammals: implications for nitrogen cycling

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9–1.1) and 2.7 (2.6–2.9) kg Nha⁻¹ year⁻¹ from feces and urine, respectively, for a total contribution of 3.7 (3.5–4.0) kg Nha⁻¹ year⁻¹. Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.     

Nitrogen inputs to a marine embayment: the importance of groundwater

We examined the importance of nitrogen inputs from groundwater and runoff in a small coastal marine cove on Cape Cod, MA, USA. We evaluated groundwater inputs by three different methods: a water budget, assuming discharge equals recharge; direct measurements of discharge using bell jars; and a budget of water and salt at the mouth of the Cove over several tidal cycles. The lowest estimates were obtained by using a water budget and the highest estimates were obtained using a budget of water and salt at the Cove mouth. Overall there was more than a five fold difference in the freshwater inputs calculated by using these methods. Nitrogen in groundwater appears to be largely derived from on site septic systems. Average nitrate concentrations were highest in the region where building density was greatest. Nitrate in groundwater appeared to behave conservatively in sandy sediments where groundwater flow rates were high (> 11/m²/h), indicating that denitrification was not substantially reducing external nitrogen loading to the Cove. Nitrogen inputs from groundwater were approximately 300 mmol-N/m³/y of Cove water. Road runoff contributed an additional 60 mmol/m³/y. Total nitrogen inputs from groundwater and road runoff to this cove were similar in magnitude to river dominated estuaries in urbanized areas in the United States.     

嫁接与施氮对甜瓜产量和氮素吸收、利用的影响

通过裂区设计田间试验,主区为2种栽培方式(嫁接栽培和自根栽培),副区为4个施氮水平(0、120、240、360 kg N·hm^-2),研究了栽培方式和施氮量对甜瓜产量和品质、氮素运移和分配,以及氮素利用率的影响.结果表明: 嫁接栽培的甜瓜商品瓜产量较自根甜瓜提高了7.3%,可溶性固形物含量降低了0.16%～3.28%;生长前期嫁接栽培甜瓜氮素累积量较自根栽培低,结果后嫁接栽培氮素累积量显著升高,收获时植株氮素累积量较自根栽培增加了5.2%,果实中的氮素累积量提高了10.3%;嫁接栽培植株氮素向果实的转移量较自根栽培提高了20.9%,嫁接栽培果实中的氮素分配率在80%以上,自根栽培的分配率在80%以下;在同一施氮水平下,嫁接栽培的甜瓜氮素吸收利用率较自根栽培提高了1.3%～4.2%,氮素农学效率提高了2.73～5.56 kg·kg^-1,氮素生理利用率提高了7.39～16.18 kg·kg^-1;从商品瓜产量、氮素吸收量和氮素利用率综合考虑,施氮量240 kg·hm^-2为本区域嫁接甜瓜较适宜的氮素用量.     

Time course of N2 fixation in common bean (Phaseolus vulgaris L.)

Field and greenhouse experiments were conducted to assess the nitrogen fixation rates of four cultivars of common bean (Phaseolus vulgaris L.) at different growth stages. The ¹⁵N isotope dilution technique was used to quantify biological nitrogen fixation. In the greenhouse, cultivars M4403 and Kallmet accumulated 301 and 189 mg N plant^–1, respectively, up to 63 days after planting (DAP) of which 57 and 43% was derived from atmosphere. Under field conditions, cultivars Bayocel and Flor de Mayo RMC accumulated in 77 DAP, 147 and 135 kg N ha^–1, respectively, of which approximately one-half was derived from the atmosphere. The rates of N₂ fixation determined at different growth stages increased as the plants developed, and reached a maximum during the reproductive stage both under field and greenhouse conditions. Differences in translocation of N were observed between the cultivars tested, particularly under field conditions. Thus, the fixed N harvest index was 93 and 60 for cultivars Flor de Mayo and Bayocel, respectively. In early stages of growth, the total content of ureides in the plants correlated with the N fixation rates. The findings reported in the present paper can be used to build a strategy for enhancing biological N₂ fixation in common bean.     

The cycling of organic nitrogen through the atmosphere

Atmospheric organic nitrogen (ON) appears to be a ubiquitous but poorly understood component of the atmospheric nitrogen deposition flux. Here, we focus on the ON components that dominate deposition and do not consider reactive atmospheric gases containing ON such as peroxyacyl nitrates that are important in atmospheric nitrogen transport, but are probably not particularly important in deposition. We first review the approaches to the analysis and characterization of atmospheric ON. We then briefly summarize the available data on the concentrations of ON in both aerosols and rainwater from around the world, and the limited information available on its chemical characterization. This evidence clearly shows that atmospheric aerosol and rainwater ON is a complex mixture of material from multiple sources. This synthesis of available information is then used to try and identify some of the important sources of this material, in particular, if it is of predominantly natural or anthropogenic origin. Finally, we suggest that the flux of ON is about 25 per cent of the total nitrogen deposition flux.