不同类型红富士苹果对春季土施~(15)N-尿素的吸收、分配和利用特性研究

以15年生"惠民短枝"(短枝型)和"长富10"(普通型)红富士苹果/平邑甜茶(M.domesticaBorkh.cv.RedFuji/M.hupenensisRhed)为试材,研究其对春季土施15N-尿素的吸收、分配与利用特性。结果表明,盛花期短枝型和普通型红富士均以细根中吸收的氮素来源与肥料的比例(Ndff)值最高,分别为0.407%和0.286%,短枝型显著高于普通型;新梢旺长期和花芽分化期,根部吸收的15N优先向新生营养器官运转,短枝型红富士,除叶片外,其余各器官中Ndff值均高于普通型;果实膨大期和果实采收期,短枝型和普通型红富士均以果实中Ndff值最高,短枝型高于普通型;采收后,短枝型和普通型红富士均以粗根中Ndff值最高,分别为0.902%和0.792%,短枝型高于普通型。不同物候期短枝型和普通型红富士吸收的15N在各器官的分配率存在差异,盛花期贮藏器官15N分配率最高,两品种差异不显著;新梢旺长期和花芽分化期,短枝型和普通型红富士贮藏器官15N的分配率不断下降,15N主要向营养器官分配,短枝型低于普通型;果实膨大期和果实采收期短枝型和普通型红富士生殖器官成为新的分配中心,短枝型显著高于普通型;采收后15N向贮藏器官回流、积累,短枝型红富士贮藏器官能积累更多的营养物质。春季土施15N-尿素,随着物候期的推移,短枝型和普通型红富士对15N尿素的吸收利用率逐渐上升,采收后达到最高,分别为24.643%和16.311%;短枝型红富士氮素利用率普遍高于普通型。     

Organic C and N stabilization in a forest soil: Evidence from sequential density fractionation

In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model).To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm⁻³ and analyzed the six fractions for measures of organic matter and mineral phase properties.All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and ¹⁴C mean residence time (MRT) increased with particle density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, ¹³C and ¹⁵N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an “onion” layering model.X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.     

Bi-directional nitrogen transfer in an intercropping system of peanut with rice cultivated in aerobic soil

Three separate greenhouse experiments were conducted to determine the bi-directional N transfer in a peanut and rice intercropping system using the direct ¹⁵N foliar feeding technique at N application rates of 15, 75 and 150 kg ha^–1. When peanut was used as the ¹⁵N donor plant, the atom % ¹⁵N in the rice shoot was consistently higher than in control rice, indicating that ¹⁵N transfer from peanut to the associated rice crop occurred. The percentage of N transfer (%NT) from peanut to the associated rice was 9.9%, 5.7% and 4.2% at the three N application rates, respectively. The N transferred from peanut to rice was 22.6, 15.5 and 8.2 mg N plant^–1, accounting for 10.9%, 6.4% and 3.1% of the total N accumulated in rice plants at the three N application rates, respectively. When rice functioned as the ¹⁵N donor plant, the %NTs were 4.4%, 2.1% and 1.4% and represented about 5.2%, 3.4% and 2.4% of total N accumulated in peanut shoot at the three N application rates, respectively. The net directional N transfer was from peanut to rice and this was calculated by the difference in the bi-directional transfers and was mainly due to peanut root decomposition. Thus, the %NTs were 10.7%, 6.3%, 5.1% and 3.5% on 28 July (the day on which peanut shoots were cut), 8 August, 28 August and 8 September, respectively, and correspondingly, the N transferred from peanut to rice represented 6.0%, 5.8%, 5.1% and 3.2% of the total N accumulated in the rice plants.     

Denitrification in intact subsoil cores

 Intact, unamended subsoil cores taken from two contrasting field sites were incubated in the laboratory at 12  °C under aerobic (21% O₂) and anaerobic (1.1–5.5% O₂) conditions. Denitrification of ¹⁵N-NO₃ ^– diffusing into the cores across a semi-permeable membrane was estimated by: (1) direct observation of ¹⁵N-labelled N₂ and N₂O, and (2) mass balance following sectioning at the end of the experiment. The in situ denitrification potential (rates where the supply of NO₃ ^– is not limited by diffusion) was estimated using a finite-difference approximation to a diffusion reaction equation based on comparison of time and depth profiles of NO₃ ^– and Br^– in the incubated cores. Potentials between 0.2 and 2.5 mg N kg^–1 day^–1 were obtained under low O₂ and natural C concentrations. These results indicate the potential for denitrification in glacial till subsoils to reduce NO₃ ^– leaching to ground or surface waters to levels unlikely to result in a pollution hazard. The major product of NO₃ ^– reduction in these subsoils was observed to be N₂, rather than the greenhouse gas and catalyst of stratospheric O₃ removal, N₂O. Received: 31 October 1997     

Volatilization losses of surface-applied urea nitrogen from Vertisols in the Indian semi-arid tropics

The N loss from Vertisols was estimated by measuring the loss of ¹⁵N-labelled urea N under conditions that promote NH₃ volatilization. Urea granules were placed on the top of 150-mm deep soil columns (Vertisols) collected from three sites with a range in pH, electrical conductivity, and cation exchange capacity. There were two contrasting moisture treatments, one near field capacity (wet) and another with intermittent wetting of the soil surface before allowing the columns to dry (moist-dry). The results indicated that losses were influenced markedly by pH and moisture treatment, being 29.5, 33.5, and 33% from the wet soils and 37, 42, and 40.5% from the moistdry soils with pH values of 7.7, 8.2, and 9.3, respectively. These observations clearly indicate that broadcasting of urea on the surface of Vertisols may cause substantial N losses.     

稻草和尿素配施时水稻对肥料氮和土壤氮的吸收利用

利用＾１５Ｎ同位素示踪技术,研究了稻草和尿素配施时水稻对肥料和土壤氮的吸收。结果表明,稻草单施导致土壤速效氮的生物固定,氮素供应不足是影响水稻分蘖成穗的限制因子,稻草配合尿素施用,明显改善肥料氮和土壤氮的供应,既有利于当季水稻增产,也有利于培养土壤肥力,还有利于后茬物作产量的提高 。     

Heterotrophic and autotrophic nitrification in two acid pasture soils

Laboratory incubation experiments, using ¹⁵N-labeling techniques and simple analytical models, were conducted to measure heterotrophic and autotrophic nitrification rates in two acid soils (pH 4.8-5.3; 1/5 in H₂O) with high organic carbon contents (6.2-6.8% in top 5 cm soil). The soils were from pastures located near Maindample and Ruffy in the Northeast Victoria, Australia. Gross rates of N mineralization, nitrification and immobilization were measured. The gross rates of autotrophic nitrification were 0.157 and 0.119 μg N g⁻¹ h⁻¹ and heterotrophic nitrification rates were 0.036 and 0.009 μg N g⁻¹ h⁻¹ for the Maindample and Ruffy soils, respectively. Heterotrophic nitrification accounted for 19% and 7% of the total nitrification in the Maindample and Ruffy soils, respectively. The heterotrophic nitrifiers used organic N compounds and no as the substrate for nitrification.     

稀土对碳酸氢铵增效作用的研究

应用15N示踪法研究稀土与碳铵混配的情况下稀土对碳铵氮素的增效作用。结果表明 ,稀土碳铵促进了作物根系生长 ,使根的干物重比不添加稀土的对照提高7 3 4%～ 2 7 8% ,产量提高 4 1 7%～ 6 3 0 %。在谷子和小麦试验中 ,稀土碳铵中的氮素利用率分别比对照提高 8 84%和 5 2 4% ,差异达到显著水平。表明稀土与碳铵混配施用时 ,稀土对碳铵有增效作用     

水稻‘甬优15’分期播种的气象条件适宜性试验研究

研究旨在通过分期播种试验,得到水稻‘甬优15’在本地播种最适宜播期,以提高其产量及品质。根据2016—2020年龙游国家农业气象试验站‘甬优15’分期播种试验数据和2018—2019年水稻品质数据,通过对比试验,得到‘甬优15’的产量与品质和播期的关系。结果表明：（1）播期对‘甬优15’的全生育天数和灌浆期天数有一定影响,主要表现为播期越晚全生育天数减少,灌浆期延长;（2）22℃是灌浆期水稻正常发育阈值,低于22℃的灌浆期平均气温会明显增加水稻灌浆乳熟时间;（3）‘甬优15’水稻直链淀粉含量普遍在10%左右,较易糊化,蛋白质含量接近7%,口感与营养含量较为平衡;（4）当播期推迟至6月中旬之后,‘甬优15’产量有明显降低,品质也有所下降;（5）‘甬优15’播种期控制在5月下旬6月上旬,能明显改善龙游本地单季晚稻产量。     

板蓝根多糖的提取及其对猪细小病毒的体外作用

用水煮醇沉法提取板蓝根多糖,通过观察PK-15细胞病变效应（CPE）来评价板蓝根多糖的不同加药方式体外对猪细小病毒（PPV）的阻断和抑制作用。结果表明板蓝根多糖在对细胞的安全浓度范围内,对猪细小病毒有明显的阻断作用和抑制的作用,最小的阻断浓度为2.09μg/ml,最小的抑制浓度为4.19μg/ml。