The effect of an intermittent water-table gradient on soil and xylem nitrate in cotton

Summary Cotton (Gossypium hirsutum cv Deltapine 61) was grown in a sloping plot of soil in the field to examine the effect of a gradient of water-table depth on soil nitrate availability and plant uptake during two periods of the growing season. Before the water-table was imposed NO₃ was less concentrated at the lower end of the sloping plot. This was attributed to slow denitrification at microsites within the soil at the lower end which was wetter than further up the plot. At flooding NO₃ disappeared only slowly due to a carbon substrate limitation to denitrification in the soil. This loss occurred primarily in areas where the water-table was high and oxygen concentration in the soil solution was low. Plant NO₃ uptake, assessed by measuring the concentration in the xylem, parallelled the distribution of NO₃ in the soil solution. Under high water-tables xylem NO₃ levels fell but it was not possible to say whether this was due to impaired root function or to the reduced concentration of NO₃ observed in the soil solution. At intermediate water-table depths where soil NO₃ availability remained high xylem NO₃ concentration fell relative to the well drained control plants, suggesting that flooding had damaged the root system.Manufactured by Merck. Mention of commerical names does not imply endorsement by either CSIRO or USDA.     

The effect of sulphide on nitrate reduction in soil

Summary Soil, amended with sodium sulphide, was incubated anaerobically with added nitrate, and the nitrogenous endoproducts-gaseous-N, nitrate-, nitrite- and ammonium-N—measured.Sulphide depressed gaseous-N production (denitrification), but stimulated the reduction of nitrate to ammonium, and, to a lesser extent, to nitrite.Saskatchewan Institute of Pedology Publication No. R84.     

The impact of crop plant cultivation and peat amendment on soil microbial activity and structure

A rapid means for restoring soil fertility could be addition of peat to the plough layer. The impact of cultivation of eight different crops (the joint impact of plant and the management tailored for each plant), with and without soil amendment by peat treatment on soil microbiological, physical and chemical properties was assessed for two consecutive growing seasons. As a measure of the functional diversity of soil microbial community we estimated the activity of several different extracellular soil enzymes using the ZymProfiler® test kit. ATP content was measured to yield information on the amount of the active microbial biomass, and phospholipid fatty acid (PLFA) profiles were analysed to reveal the microbial community structure. The enzyme activity patterns of the soil samples indicated several differences due to the different crops and years but ATP content and PLFA profiles were rather stable. However, microbial biomass as total amount of PLFAs depended on the plant and peat treatment and ATP content varied between the years. The effects of the peat treatments were less clearly indicated by the biological parameters one or two years after the amendment, as only arylsulphatase and β-xylosidase activities were affected in both the years. Soil moisture, affecting enzyme activities, depended on the year and crop plant and peat addition increased it. Abbreviations: AMC – 7-amino-4-methylcoumarin; AP – aminopeptidase; ATP – adenosine triphosphate; C_mic– microbial biomass carbon; DNA – deoxyribonucleic acid; EC – electrical conductivity; FAME – fatty acid methyl ester; fw – fresh weight; MUF – 4-methylumbelliferyl; na – not added; N_mic– microbial biomass nitrogen; PDE – phosphodiesterase; PLFA – phospholipid fatty acid; PME – phosphomonoesterase; SOM – soil organic matter     

The effect of soil inoculation with microbial pesticide destructors on plant growth and development]

Soil inoculation with liquid cultures of Bacillus megaterium 501 and Exophiala nigrum A-29 capable of degrading several organophosphorus pesticides accelerated growth and development of experimental plants, formation of their generative organs, and improved their productivity. This was particularly observed under stress plant growth conditions on phytotoxic peach substrates. The microorganisms inoculated can probably degrade phytotoxins present in soils, thereby favoring the plant development.     

Effect of phosphoros nutrition in peat on tomato plant growth and fruit development

Summary The effect of P nutrition on the growth of tomato plants in peat was examined. Initially, plants received an adequate supply of P and then received either nil, 0.78 or 2.34 kg superphosphate per m³ in combination with either 50 g N/ml (N₁) or 300 g N/ml (N₂) as ammonium nitrate in a liquid feed. Vegetative growth was restricted in the lower P treatmentsi.e. inhibited shoot growth, reduced duration of leaf expansion phase, thinner stems and reduced vegetative dry wt. Plants receiving N₂ showed a greater restriction in growth compared with N₁ plants when the P supply was limiting. P deficiency disrupted protein metabolism in the leaves, in that soluble leaf protein was reduced and trichloroacetic acid-soluble N accumulated. Flower development was accelerated by low P applications but the final numbers of flowers and the fruit-setting efficiency were reduced. Lowering the N supply reduced the fruit yield by 36 per cent while an intermediate P level reduced yields by about 15 per cent. Maximum fruit yields and good vegetative growth occurred when plants contained 0.4 per cent P or above in the mature leaves, and this value was achieved by adding the highest level (2.34 kg/m³) of superphosphate to the peat.     

The effect of sulfate and nitrate on methane formation in a freshwater sediment

A freshwater sediment from a ditch of a peat grassland near Zegveld (Province of Utrecht, The Netherlands) was investigated for its potential methanogenic and syntrophic activity and the influence of sulfate and nitrate on these potential activities. Methanogenesis started after a 10 days lagphase. After 35–40 days aceticlastic methanogens were sufficiently enriched to cause a net decrease of acetate. In the presence of sulfate methane formation was only slightly affected. The addition of nitrate led to an outcompetion of aceticlastic methanogens by nitrate reducers. When inorganic electron acceptors were absent, substrates like propionate and butyrate were converted by syntrophic methanogenic consortia. Addition of inorganic electron acceptors resulted in an outcompetition of the syntrophic propionate and butyrate degrading consortia by the sulfate and nitrate reducers.     

Distribution and development of nitrate reductase activity in germinating cotton seedlings

Activity of nitrate reductase in roots and cotyledons of cotton seedings (Gossypium hirsutum L. cv. Deltapine 16) increased rapidly on germination, reaching a maximum after 1 day of imbibition. Thereafter, activity declined until emergence and greening of the cotyledons, when it again began to increase steadily. Germinating soybean (Glycine max (L.) Merrill cv. Merit) and sunflower (Helianthus annuus L. cv. Peredovic) seedlings did not show the early peak of activity. The early peak depended on nitrate and was sensitive to cycloheximide, but not to actinomycin D or other inhibitors of RNA synthesis. The second, light-dependent increase was sensitive to actinomycin D. In roots, the early peak of activity occurred before any growth. After emergence of the root tip from the seed coat, activity was localized in the terminal 2 millimeters, whether expressed on a fresh weight, protein, or root basis. The difference in activity between the apical (0-2 millimeter) and subapical (2-4 millimeter) segments did not result from differences in nitrate availability, energy supply, or turnover rates of nitrate reductase. Root activity was similar to that of the cotyledons after emergence, in that both were sensitive to actinomycin D.     

The effect of forestry drainage on vertical distributions of major plant nutrients in peat soils

Vertical distributions of total N, P, K, Ca and Mg in a 0–60 cm surface peat layer were studied at 80 pine mire sites in southern Finland. The sites fell into two categories according to the soil nutrient regime: Meso-oligotrophic and oligo-ombrotrophic, and formed a chronosequence from undrained sites to sites drained 55 years ago. A statistically significant drainage age effect on the gravimetric (mg g-1) concentration profile forms was detected for all nutrients except K. In oligo-ombrotrophic sites the concentration of N increased following drainage in the topmost layer (0–10 cm) and that of P in all layers. In meso-oligotrophic sites the changes in N and P profiles were obscure. The concentration profiles of K remained clearly surface-enriched in both site type groups, but there was a general drop in the concentration values immediately after drainage. Ca and Mg decreased, especially in the 10–20 and 25–35 cm layers in both site type groups. The volumetric (kg m-3) nutrient concentrations clearly reflected the increase in the bulk density of the surface peat occurring after drainage. The compaction of peat had compensated for the effect of the processes removing nutrients from the soil (increased tree stand uptake, leaching); for Ca and Mg to a lesser degree than for the other nutrients. It was concluded that the N, P and K profiles did not show changes that would be likely to affect site productivity, whereas the net loss of Ca and Mg may cause problems in the longer term. As the total K capital of the sites was in general rather small, a disturbance in the biological cycle, such as cutting of the tree stand, may be critical. This revised version was published online in August 2006 with corrections to the Cover Date.     

有机、无机氮肥施用对苜蓿产量、土壤硝态氮和温室气体排放的影响

2012年5月—2014年6月,采用田间小区试验方法,研究了不同氮肥管理对N₂O与CH₄的排放、土壤硝态氮含量以及苜蓿干草产量的影响.试验共设5个处理:对照(CK)、单施尿素处理(100 kg N·hm^-2, CF)、尿素(100 kg N·hm^-2)与腐熟牛粪(60 kg N·hm^-2)混施处理(DM₁)、尿素(100 kg N·hm^-2)与沼液(60 kg N·hm^-2)混施处理(DT)及减量尿素(40 kg N·hm^-2)与牛粪(60 kg N·hm^-2)混施处理(DM₂).结果表明: 与CK相比,CF、DM₁、DT和DM₂处理苜蓿干草产量分别增加44.2%、38.9%、56.3%和30.6%,N₂O排放分别比对照增加52.2%、89.1%、133.7%和59.4%,但各施肥处理对甲烷吸收表现出不同程度的抑制作用.苜蓿生产中,尿素和牛粪处理N₂O-N排放与肥料氮素投入量比值(排放系数)为0.25%～0.28%,而沼液处理N₂O-N排放系数为0.64%,显著高于前者.苜蓿生产中,施用化肥或有机无机混施均能显著增加苜蓿干物质产量,土壤硝态氮深层淋洗风险较小,但增加了CO_2-equivalent净排放量.     

Independent control of fiber development and nitrate reduction in cultured cotton ovules

Several lines of evidence implicate ammonium as an important factor in the growth and development of cotton (Gossypium hirsutum L.) ovules cultured in vitro. For example, ovules cultured at 28 C require indoleacetic acid (IAA) and either ammonium or gibberellic acid (GA₃) in the medium for fiber development, whereas ovules cultured at 34 C require only IAA. Because of this effect of ammonium supply, it seemed possible that hormones or increased temperature were also promoting the availability of reduced nitrogen by induction of increased nitrate reductase activity in the ovules. This possibility was tested.     

Modelling the uptake of nitrate by a growing plant with an adjustable root nitrate uptake capacity

A new model is presented to predict the plant uptake of nitrate supplied by diffusion and mass flow to its roots. Plant growth, root-shoot ratio and the plant's nitrate uptake capacity are all set dependent on the plant's N nutrition state. By thoroughly integrating processes occurring in both plant and soil, the model enables to control the relative importance of both under a wide range of different nutritional scenarios.Soil parameters D₀ diffusion coefficient in water (m² day^-1) - D_e diffusion coefficient in soil (m² day^-1) - C nitrate concentration in soil (mol m^-3) - f tortuosity (-) - volumetric moisture content (-) - R radial distance from root axis (m) Plant parameters b₁, b₂ parameters of biomass partitioning Equation (10) - IR interroot distance (m) - K_mU Michaelis-Menten constant of the uptake system (mol m^-3) - K_mNRA Michaelis-Menten constant of nitrogen reduction system (mol g^-1) - k₁, k₂, k₃ parameters of growth model Equation (9) - L_v Root length density (m m^-3) - NO_{3 set} ^- Set point of the cytoplasmatic nitrate pool (mol g^-1 dw) - NO_{3 c} ^- cytoplasmatic nitrate concentration (mol g^-1 dw) - NO_{3 v} ^- vacuolar nitrate concentration (mol g^-1 dw) - NRA_max maximum nitrate reductase activity (mol g^-1 dw day^-1) - N_re reduced nitrogen content (mol) - N_remax maximum reduced N concentration in the plant (mol g^-1 dw) - P partitioning coefficient of nitrate between cyplasm and vacuole - R(1) root radius (m) - RGR relative growth rate (day^-1) - U uptake rate (mol day^-1 m^-2) - U_max maximum uptake rate (Eq. 6) (day^-1 m^-2) - Vo water flux at root surface (m day^-1) - W_r root dry weight (g) - W_sh shoot dry weight (g) - X model parameter: number of root compartments - Y model parameter: number of nodes     

A rapid method for determination of nitrate in soil and plant extracts

A rapid colourimetric method of determination of nitrate was modified. Proposed modifications eliminated the use of barium sulphate and introduced diazotization of sulphanilamide by the nitrite ion obtained by the reduction of nitrate and subsequent coupling with N-1-naphthyethelenediamine dihydrochloride. Introduction of filtration in place of centrifugation of coloured solution simplified the procedure. Determinations were highly reproducible with coefficient of variation of 2.2 and 2.9% for soil and plant extracts respectively.     

Interferences between Sphagnum and vascular plants: effects on plant community structure and peat formation

The interference between vascular plants and peat mosses with respect to nitrogen and phosphorus was studied in a fertilization experiment and with respect to competition for light in a removal experiment in poor fens with either soligenous or topogenous hydrology using Narthecium ossifragum (L.) Huds. and three species of Sphagnum sect. Sphagnum as targets. Adding fertilizer either on the moss surface or below it confirmed the hypotheses of an asymmetric competition for nutrients, viz. that the Sphagnum mosses relied on the atmospheric supply while Narthecium depended on mineralization in the peat. The results of the removal experiments and the negatively correlated growth of Narthecium and Sphagnum mosses demonstrated a symmetric competition for light. The intensity of the competition for light increased as the availability of N and P increased. The nutrient resources in the total biomass decreased with decreasing standing crop of Narthecium . Only with a considerable amount of mineral nutrients in the biomass has Narthecium the capacity to grow ahead of Sphagnum, because the asymmetric competition for N and P gives Sphagnum the capacity to reduce the performance of vascular plants. The mosses are more efficient in their use of nutrients and produce a decay-resistant litter inducing low mineralization and increasing the peat accumulation rate, and that withdraws N and P from the rhizosphere. The Sphagnum mosses thus act as ecological engineers structuring the plant community and determining the carbon balance of the system. The development of ombrotrophic conditions through peat accumulation seems less probable on soligenous than on topogenous mires owing to the higher mineralization rate there supporting the growth of the vascular plants. Correspondingly, disturbances of the Sphagnum cover, such as through airborne pollutants, increase the productivity of the vascular plants and decrease the capacity for carbon accumulation.