氮肥不同施用技术对直播水稻氮素吸收及其产量形成的影响

应用15N示踪技术研究了不同氮肥施用技术对直播水稻氮素吸收及其产量形成的影响。结果表明 ,在氮肥用量相同的情况下 ,采用“一基三追” ,即在施基肥的基础上 ,追施苗肥、蘖肥和穗肥的施用技术能促进直播稻均衡生长 ,增加穗数 ,粒数和粒重 ,是一种适合直播水稻高产栽培的施肥技术。     

冬小麦节水灌溉制度下不同施氮量的氮素平衡

用15N示踪技术研究了节水灌溉条件下冬小麦对不同施氮量的氮素吸收和氮素平衡 ,并比较了两种灌溉制度下小麦对节肥施氮量的吸收动态。结果表明 ,与常规施氮量处理相比 ,节水灌溉条件下节肥施氮量处理的氮肥损失率降低 ,氮肥当季利用率和土壤残留率提高 ;基施氮肥的利用率高于追施氮肥 ;土壤肥料氮的残留率在 2 9%～ 41 %之间 ,分布于 1m土层中 ,其中60 %以上集中在 0～ 2 0cm土层 ;在整个小麦生长季内 ,肥料氮并没有淋洗到 1 30m以下。节肥施氮量在常规灌溉下的当季利用率比在节水灌溉下降低 1 6 6%。     

应用~(15)N研究小麦花生两熟制氮肥分配方式对小麦、花生产量及N肥利用率的影响

在小麦花生两熟制条件下 ,全年氮肥两作 3次施用 (小麦基肥、追肥和花生基肥 )氮素利用率为 3 2 52 % ,一作两次施用 (小麦基肥和追肥 )氮素利用率为 3 7 0 1 % ,但前者土壤残留多 ,损失少 ,氮肥回收率为 69 2 4% ,较后者高 1 2 0 3个百分点。且前者有利于小麦、花生产量的形成 ,是小麦花生两熟制适宜的施肥方式。小麦当茬氮肥利用率为 1 6 80 %～ 3 5 63 %。夏直播花生当茬及前茬小麦基肥和追肥 (拔节期 )的氮肥利用率分别为 2 3 70 %、6 57%～ 7 70 %和 1 0 0 3 %～ 1 2 73 % ;施肥时间和施肥量对氮肥利用率影响较大     

C and N natural abundance of the soil microbial biomass

Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is ¹³C, and especially ¹⁵N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil organic matter. We developed a new approach to determine the natural abundance C and N isotope composition of the microbial biomass across a broad range of soil types, vegetation, and climates. We found consistently that the soil microbial biomass was ¹⁵N-enriched relative to the total (3.2 ‰) and extractable N pools (3.7 ‰), and ¹³C-enriched relative to the extractable C pool (2.5 ‰). The microbial biomass was also ¹³C-enriched relative to total C for soils that exhibited a C3-plant signature (1.6 ‰), but ¹³C-depleted for soils with a C4 signature (−1.1 ‰). The latter was probably associated with an increase of annual C3 forbs in C4 grasslands after an extreme drought. These findings are in agreement with the proposed contribution of microbial products to the stabilized soil organic matter and may help explain the shift in isotope composition during soil organic matter formation.     

中国亚热带红壤旱坡地花生系统尿酸氮素去向

A field experiment was conducted to study the outcome of N using isotope-labeled urea with a peanut cropping system in a Udic Ferrosol on a 7% slope at the Ecological Experimental Station of Red Soil, Chinese Academy of Sciences. The micro-plots were designed in two sets with three replicates and four N treatments. An iron frame with its edge 10 cm above the ground was used to control soil erosion and runoff in set A, but in set B the upper edge of the frame was level with the ground. Randomly positioned ^15N fertilized micro-plots were established along the contour. At harvest on August 13, 2002, which was four months after urea application, the peanuts had absorbed 30.6%-38.0% of the urea, transpired 13.1%-22.4% to the atmosphere, lost 6.4%-8.4% through soil erosion and surface runoff, and maintained 40.7%-48.9% in the 0-60 cm soil layer with 0.5%-5.0% below 60 cm.     

Comparative effects of applying leguminous and non-leguminous green manures and inorganic N on biomass yield and nitrogen uptake in flooded rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The beneficial role of green manures in rice production is generally ascribed to their potential of supplying plant nutrients, particularly nitrogen (N). However, the mechanisms through which green manures enhance the crop productivity are poorly understood. Pot experiments were conducted using a ¹⁵N-tracer technique: (1) to compare the biomass production potential of sesbania (Sesbania aculeata Pers.) and maize (Zea mays L.) as green manuring crops for lowland rice and (2) to compare the effect of the two types of green manure and inorganic N on the dry matter accumulation and N uptake by two rice (Oryza sativa L.) cultivars, viz. IR-6 and Bas-370. Although maize produced three times higher shoot biomass compared with sesbania, the latter showed higher N concentration; and thus the total N yield was similar in the two types of plants. Applying the shoot material of the two plants to flooded rice significantly enhanced the dry matter yield and N uptake by the two rice cultivars, the positive effects generally being more pronounced with sesbania than with maize amendment. The difference in the growth-promoting potential of the two plant residues was related more to an increased uptake of the native soil N rather than to their direct role as a source of plant-available N. A positive added nitrogen interaction (ANI) was observed due to both plant residues, the effect was much more pronounced with the application of sesbania than with maize residues. In both rice cultivars, inorganic N also caused a substantial ANI, particularly at higher application rate. Losses from the applied N were 2–3 times lower from sesbania, compared with maize treatment. Green manuring with sesbania also caused much lower N losses than the inorganic N applied at equivalent or higher rates. The overall benefit of green manuring to rice plants was higher than inorganic N applied at comparable rates. The two rice cultivars differed in their response to green manuring, IR-6 generally being more responsive than Bas-370.     

A survey of symbiotic nitrogen fixation by white clover grown on metal contaminated soils

There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with ¹⁵N isotope dilution in white clover (Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass (Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (N_dff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on N_dff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg⁻¹, 428 mg Cu kg⁻¹ and 10 mg Cd kg⁻¹. The N_dff was significantly reduced by increasing metal concentration in soils from two other sites where N_dff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on N_dff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg⁻¹). The variation of N_dff among all soils (n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g⁻¹ soil)), whereas correlations with total or soil solution metal concentrations were weak (R²<0.25). The is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at even at total Zn concentrations of about 2000 mg Zn kg⁻¹, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor.     

Irrigation practices may affect denitrification more than nitrogen mineralization in warm climatic conditions

Predicting the impact of irrigation practices on soil N mineralization and N balance is an important issue to optimize N fertilization and reduce the N losses towards the environment. The effect of summer irrigation on N dynamics was investigated in two arable fields in Southern France. Net N mineralization was assessed by combining frequent measurements of water and mineral N contents in soil and the use of a calculation model (LIXIM). It was first calculated assuming that denitrification was negligible. This hypothesis led to inconsistent results, apparent net N mineralized being smaller under irrigated than non-irrigated conditions and net mineralization kinetics being erratic. The occurrence of denitrification was confirmed by the use of ¹⁵NO₃ tracing in an experiment carried out in summer, including three irrigated treatments. The average ¹⁵N recovery varied from 45% to 85% and was smallest in the most frequently irrigated treatment. Over the 8-week experiment, the N losses varied from 30 to 38 kg ha⁻¹ in the irrigated treatments. They were satisfactorily simulated by a simple denitrification model (NEMIS). Combining the LIXIM model and the simulated or calculated denitrification allowed to predict satisfactorily the evolution of soil mineral N accounting for the effects of temperature and moisture. The net N mineralized for 8 weeks varied from 34 kg N ha⁻¹ in the un-irrigated to 46 kg N ha⁻¹ in the irrigated treatments. The drying–rewetting cycles did not induce a flush of N mineralization. Our results suggest that denitrification has to be accounted for in irrigated systems, particularly in warm conditions and when the topsoil contains high nitrate contents.     

Dinitrogen and N2O emissions in arable soils: Effect of tillage, N source and soil moisture

A laboratory investigation was performed to compare the fluxes of dinitrogen (N₂), N₂O and carbon dioxide (CO₂) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0-10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with ¹⁵N-labeled fertilizers (100 mg N kg⁻¹ soil). Gas and soil samples were collected at 1-4 day intervals during the incubation period. The N₂O and CO₂ fluxes were measured by a gas chromatography (GC) system while total N₂ and N₂O losses and their ¹⁵N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N₂ and N₂O were significantly affected by tillage, N source and soil moisture. We observed higher (P<0.05) fluxes of N₂+N₂O, N₂O and CO₂ from the NT soils than from the CT soils. Compared with the addition of nitrate (NO₃⁻), the addition of ammonium (NH₄⁺) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH₄⁺ on the N₂ and/or N₂O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N₂O emission under the lower moisture condition. Total and fertilizer-induced emissions of N₂ and/or N₂O were higher (P<0.05) at 75% WFPS than with 60% WFPS, while CO₂ fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N₂O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO₃⁻ form of N fertilizer would reduce potential N₂O emissions from arable soils.     

不同灌溉方法对不同氮肥在温室土壤-植株中的氮素分配影响

以番茄为供试作物,采用田间微区试验的方法研究了不同灌溉方法和不同氮肥种类对氮素在土壤不同层次间的残留以及在番茄植株不同部位之间的分配。结果表明,在番茄整个生育期内,土壤中无机氮主要以NO3--N的形式存在,NH4+-N所占比例很小。0～100cm土层中,滴灌和沟灌各处理土壤中NH4+-N的含量在整个生育期内含量均比较低(低于6mgkg-1),且变化幅度不大,各土层NH4+-N的含量受灌溉方式和施肥的影响较小。无论是滴灌还是沟灌,番茄全生育期内0～20cm土层土壤NO3--N含量始终较高。沟灌易引起土壤中NO3--N向下层迁移,而滴灌对40～60cm土层及其以下各层次土壤的NO3--N分布影响作用不明显。硝态氮肥较铵态氮肥和酰胺态氮肥更易随水向深层土壤迁移。灌溉方式对肥料15N在果实、茎、叶中的分配比例没有明显影响,肥料15N在番茄地上部分各器官所含的量以果实为最高,其次为叶,茎中的含量最少;两种灌溉方法间肥料15N在果实、茎、叶的分配比例差异不大,平均为2.9∶1∶1.6。