Comparison of the efficiency of urea,aqueous ammonia and ammonium sulphate as nitrogen fertilizers

Summary Nitrogen-15 labelled urea, aqueous NH₃ and (NH₄)₂SO₄ were applied to soils contained in pots. The fertilizers were injected in 5 cm³ of solution, 3.5 cm below the soil surface, to simulate a fertilizer band in the field. Ryegrass (Lolium perenne) was planted, and several cuttings and roots were harvested. Efficiency was determined as the recovery of fertilizer-N in the plant tissues and soil.Total recovery varied from 94 to 100%. There was no significant difference between the total recovery of the 3 fertilizer forms, although recovery in the soil component was lower for (NH₄)₂SO₄ than for urea or NH₃. There was a significant difference in total recovery between soils due to the soil component. Only small amounts of¹⁵N were not recovered, whereas laboratory experiments reported elsewhere had demonstrated that substantial gaseous losses of N as N₂, N₂O and NO +NO₂ occurred in these soils during nitrification of added NH₃ fertilizer.     

Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Summary Soil pH, NH ₄ ⁺ and NO ₃ ⁻ concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH₄NO₃, (NH₄)₂SO₄, NH₄Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO ₃ ⁻ . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha⁻¹ with spring NH₄NO₃ at soil pH 6.0 to 7.65 Mgha⁻¹ with spring NH₄Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis. Oregon Agric. Exp. Stn. technical paper no. 7707.     

Replacement of nitrate by ammonium as the nitrogen source increases the salt sensitivity of pea plants. I. Ion concentrations in roots and leaves

Pea seedlings (Pisum sativum L. cv ‘Kleine Rheinlän-derin’) were grown hydroponically in solutions containing either nitrate (3 or 14 mol m⁻³) or ammonium (3 mol m⁻³) as the nitrogen source. Ammonium nutrition as such had no negative effect on plant biomass production, but drastically increased the sensitivity to moderate salinity (50 mol m⁻³ NaCl). The reasons for this effect are investigated here and in a subsequent paper. The appearance of visible symptoms of salt damage (wilting of marginal leaf areas followed by progressive necrosis) was paralleled by the development of several characteristic modifications in the solute and metabolite contents. Major changes were: (i) high salt (NaCl) accumulation in leaves; (ii) accumulation of ammonium (up to 20 mol m⁻³) and amino acids (up to 110 mol m⁻³) in leaves, but at decreased ammonium uptake rates; and (iii) decreased protein content. In a comparison paper we report on the subcellular distribution of salts, ammonium and metabolites under the above conditions.     

Variations in the natural abundance of 15N in ryegrass/white clover shoot material as influenced by cattle grazing

Biological N2 fixation in clover is an important source of N in low external-N input farming systems. Using the natural 15N-abundance method, variations in N2 fixation were investigated in grazed and mowed plots of a ryegrass/white clover field. Ryegrass 15N varied considerably, from 0.2 to 5.6 under mowed conditions and from –3.3 to 11.6 under grazed conditions. Variations in 15N white clover were lower than in ryegrass, especially in the mowed plots (SE = 0.05, n = 20). The variations in the percentage of nitrogen derived from the atmosphere (%Ndfa) in white clover were highest in the grazed plots where it ranged from 12 to 96% (mean = 64%) compared with the mowed plots where it ranged from 64 to 92% (mean = 79%). Thus, the N2 fixation per unit white clover DM in the grazed ley was lower and more variable than under mowing conditions.Urine from dairy cows equivalent to 0, 200, 400 and 800 kg N ha-1 was applied to a ryegrass/white clover plot 6, 4 or 2 weeks before harvest. Without urine application 15N of ryegrass was positive. By increasing urine application (15N = –1) two weeks before sampling, the 15N of ryegrass decreased strongly to about –7 (P < 0.001). However, this effect was only observed when urine was applied two weeks before sampling. When applying 800 kg N four and six weeks before sampling, 15N in ryegrass was not significantly different from the treatment without urine application. White clover 15N was unaffected by whatever changes occurred in 15N of the plant-available soil N pool (reflected in 15N of ryegrass). This indicates that within the time span of this experiment, N2 fixation per unit DM was not affected by urine. Therefore, newly deposited urine may not be the main contributing factor to the variation in %Ndfa found in the grazed fields. This experiment suggested that the natural abundance method can be applied for estimating %Ndfa without disturbance in natural animal-grazed systems.     

Protein secretion in Bacillus subtilis as influenced by the combination of signal sequence and the following mature portion

Abstract We have constructed secretion vector plasmids that have the signal sequence of the Bacillus licheniformis penicillinase gene ( penP ) or the Bacillus stearothermophilus α-amylase gene ( amyT ). We have also constructed penP, amyT and hsa (human salivary α-amylase gene) cartridges. Each of these cartridges was cloned on secretion vectors in Bacillus subtilis , and enzyme production was examined. When amyT vector was used, nearly the same efficiency of enzyme secretion was observed for amyT and penP cartridges. When penP vector was used, enzyme secretion for amyT decreased to about 3% of that for penP cartridges. The eukaryotic gene hsa was hardly expressed in any secretion vectors in B. subtilis .     

控释尿素条施深度对鲜食玉米田间氨挥发和氮肥利用率的影响

为提高鲜食玉米一次性施肥的氮肥利用率并降低氮肥的环境影响,通过田间试验,以不施氮处理为对照(CK),研究了控释尿素不同条施深度(0、5、10、15、20 cm)对鲜食玉米田间土壤氨挥发特征、鲜穗产量和氮肥利用率的影响. 结果表明: 玉米种植带和宽行非施肥带的土壤氨挥发主要发生在施肥后的前2周,而窄行施肥带的土壤氨挥发在施肥后持续约1个月. 与CK相比,控释尿素表施(0 cm)处理不仅大幅度地提高了窄行施肥带的氨挥发损失量,同时也显著增加了玉米种植带和宽行非施肥带的氨挥发损失量. 不同深度施肥处理全生育期土壤氨挥发损失总量差异较大,为3.1～25.5 kg N·hm^-2,占施氮量的1.7%～14.2%.其中控释尿素条施10、15和20 cm深度处理的全生育期土壤氨挥发损失总量相差不大,分别较表施(0 cm)和浅施(5 cm)处理显著降低了85.9%～87.8%和67.0%～71.6%. 在一定范围内增加控释尿素条施深度有利于提高鲜穗产量、植株氮积累量以及氮肥偏生产力、氮肥农学利用率和氮肥表观利用率,各指标均以15 cm深度处理最高. 综上所述,控释尿素合理深施可以显著降低氨挥发损失,提高鲜穗产量和氮肥利用效率,本研究条件下控释尿素的最适宜施用深度为15 cm.     

Regulation of growth, water use efficiency and δ13C by the nitrogen source in Casuarina equisetifolia Forst. & Forst.

Carbon isotope composition (δ¹³C) was measured in a glasshouse experiment with N₂-fixing and NO₃^–- or NH₄⁺-fed Casuarina equisetifolia Forst. & Forst plants, both under well-watered and drought conditions. The abundance of ¹³C was higher (more positive δ¹³C) for NH₄⁺- than for NO₃^– -grown plants and was lowest for N₂-fixing plants. NH₄⁺-fed plants had more leaf area and dry weight and higher water use efficiency (on a biomass basis) than N₂- and NO₃^–-grown plants and had lower water consumption than plants supplied with NO₃^–, either with high or low water supply. Specific leaf areas and leaf area ratios were higher with NH₄⁺ than with NO₃^– or N₂ as the N source. The difference observed in δ¹³C between plants grown with different N sources was higher than that predicted by theory and was not in the right direction (NH₄⁺-grown plants with a more negative δ¹³C) to be explained by differences in plant composition and engagement of the various carboxylation reactions. The more positive δ¹³C in NH₄⁺- than in NO₃^–-grown plants is probably due to a decreased ratio of stomatal to carboxylation conductances, which accounts for the lower water cost of C assimilation in NH₄⁺-grown plants.     

CAM activity and day/night changes in the ultrastructure of stem chlorenchyma of Cissus quadrangularis L. as influenced by drought

Abstract Stem chlorenchymatous cells from well-watered and water-stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52-58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress.     

Spontaneous aggregation of the mitochondrial natural ATPase inhibitor in salt solutions as demonstrated by gel filtration and neutron scattering. Application to the concomitant purification of the ATPase inhibitor and F1-ATPase

(1) The natural ATPase inhibitor (IF₁) from beef heart mitochondria has a tendency to form aggregates in aqueous solutions. The extent of aggregation and the structure of the aggregates were assessed by gel filtration and small-angle neutron scattering. IF₁ polymerization was found to depend on the salt concentrations, pH of the medium and concentration of IF₁. The higher the salt concentration, the lower the aggregation state. Aggregation of IF₁ was decreased at slightly acidic pH. It increased with the concentration of IF₁ as expected from the law of mass action. (2) Neutron scattering showed the aggregation of IF₁ in 2 M ammonium sulfate solutions. The predominant species is the dimer which has a somewhat elongated shape. (3) The Sephadex G-50 chromatography that is supposed to deprive beef heart submitochondrial particles of loosely bound IF₁ (Racker, E. and Horstman, L.L. (1967) J. Biol. Chem. 242, 2547–2551) was shown to have a limited effectiveness as a trap for IF₁. The reason was that IF₁ released from the particles formed high molecular weight aggregates that were not separated from the membrane vesicles by Sephadex G-50 chromatography. (4) The above observations provide the basis for a simple method of purification of beef heart IF₁ which combines the recovery of the supernatant from submitochondrial particles with the last three steps of the IF₁ preparation described by Horstman and Racker (J. Biol. Chem. (1970) 265, 1336–1344). The particles recovered in the sediment were deprived of IF₁ and could therefore be used for preparation of F₁-ATPase. The advantage of this method is that both IF₁ and F₁-ATPase can be prepared from the same batch of mitochondria.     

Evidence for H2O2 as the product of reduction of oxygen by alternative oxidase in mitochondria from potato tubers

Oxygen consumption by alternative oxidase (AOX), present in mitochondria of many angiosperms, is known to be cyanide-resistant in contrast to cytochrome oxidase. Its activity in potato tuber (Solanum tuberosum L.) was induced following chilling treatment at 4 °C. About half of the total O₂ consumption of succinate oxidation in such mitochondria was found to be sensitive to SHAM, a known inhibitor of AOX activity. Addition of catalase to the reaction mixture of AOX during the reaction decreased the rate of SHAM-sensitive oxygen consumption by nearly half, and addition at the end of the reaction released nearly half of the consumed oxygen by AOX, both typical of catalase action on H₂O₂. These findings with catalase suggest that the product of reduction of AOX is H₂O₂ and not H₂O, as previously surmised. In potatoes subjected to chill stress (4 °C) for periods of 3, 5 and ?8 days the activity of AOX in mitochondria increased progressively with a corresponding increase in the AOX protein detected by immunoblot of the protein.