摘要:

A bioassay procedure is described for diagnosing aluminium toxicity in soils using short term root growth in extracted soil solution. Soil solution is extracted from moist soil which has been incubated at “field capacity”; for 4 days. Soil solution extracted is divided into two portions, each of which is treated with CaCl2and H3BO3to ensure that neither Ca nor B is limiting root growth. One portion is adjusted to pH 5.5 (pH adjusted treatment) with saturated Ca(OH)2solution. Aliquots (11 ml) of each portion are separately dispensed into each of five polypropylene tubes. Seedlings (in our experimentGlycine maxcv. Forrest) of uniform root length are inserted into each tube (one per tube) and grown for 48 h. The increase in root length during the 48 h growth period (root elongation) in the unadjusted solutions is expressed as a percentage of that in the pH adjusted solutions to derive relative root elongation (RRE) ‐ an index of aluminium toxicity.

ISSN:0010-3624    

DOI:10.1080/00103629009368249

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

An experiment was conducted to determine the influence of continuous cropping and K fertilization on plants grown on coarse‐textured soils high in feldspars. The A and C horizons of Elsmere (sandy, mixed, mesic Aquic Haplustoll), Valentine (mixed, mesic Typic Ustipsamment) and Sharpsburg (fine, montmorillonitic, mesic Typic Arguidoll) soils were continuously cropped in the greenhouse with annual ryegrass (Lolium multiflorumLam.). Four K treatments (0, 18.5, 37.5 and 75.0 mg K/kg soil) were applied before planting. At approximately 4 week intervals, above ground plant tissue was harvested and analyzed for K content for a total of 12 cuttings. Potassium deficiency symptoms (marginal necrosis, spotting) eventually appeared in plants grown on all but the A horizon of the Sharpsburg soil. Continuous cropping decreased plant K concentration, averaged across all treatments, from 38 to 10 g/kg dry matter. Potassium fertilization increased K concentration in plant dry matter on the soils initially low in slowly available and exchangeable K, but did not increase biomass. Uptake was higher by plants grown on A horizons. Different K rates resulted in different cumulative K uptake on the soils initially low in available K.

ISSN:0010-3624    

DOI:10.1080/00103629009368250

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

It is commonly assumed that the adverse effect of plant residues on crop yields is largely, or partly, due to phytotoxic compounds leached from these residues or produced by their decomposition, and it has been suggested that the phytotoxic compounds responsible for reduced crop yields are aliphatic acids such as acetic acid, butyric acid, and propionic acid. To test the validity of this hypothesis, we studied the effects of different amounts of acetic acid, butyric acid, and propionic acid on seed germination and seedling growth of corn(Zea maysL.), barley (Hordeum vulgareL.), and wheat(Triticum aestivumL.) in soils. The data obtained showed that the aliphatic acids tested had adverse effects on seed germination and seedling growth only when the amounts applied were much greater than the amounts reported to occur in soils treated with plant residues. We conclude that the adverse effect of plant residues on crop yields is not due to aliphatic acids derived from these residues.

ISSN:0010-3624    

DOI:10.1080/00103629009368251

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A phosphorus sorption curve was developed to evaluate the influence of established levels of soil solution P on the development of vesicular‐arbuscular mycorrhizal (VAM) activity inLeucaena leucocephala(Lam.) de Wit grown on soil:sand mixture. The P sorption curve developed after nutrient amendment and wetting and drying treatments in the greenhouse predicted levels of P established in the soil solution more accurately than P sorption isotherm developed in the laboratory.

ISSN:0010-3624    

DOI:10.1080/00103629009368252

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A greenhouse leaching column study was conducted to compare the effects of surface‐applied langbeinite (LB), phosphogypsum (PG), Ca‐ silicate slag (SS), and calcitic lime (CL) on subsoil Al and growth of alfalfa (Medicago sativaL. ‘Florida 77') in Toula silt loam soil (Typic Fragiudult). Langbeinite was foundtobe more effective than PG in the reduction of subsoil exchangeable Al, apparently through SO42‐‐induced Al precipitation. This study demonstrated that high exchangeable Al levels are not always indicative of Al toxicity in the soil solution phase. The primary factors limiting alfalfa growth in the Toula soil were found to be surface soil pH and Mn toxicity rather than subsoil Al toxicity. The liming materials, SS and CL, effectively corrected the surface soil Mn and pH problems, but had no effect on subsoil chemical properties.

ISSN:0010-3624    

DOI:10.1080/00103629009368253

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The goal was to develop an easy, fast, and economical procedure to produce plant digests that can be accurately analyzed by plasma emission spectrometry for foliar sulfur content. The closed vessel microwave procedure described requires less than 2 hours to produce 12 digested 0.5 gram samples from the point of weighing the samples to applying them to plasma emission spectrometry analysis. The procedure utilizes nitric acid and hydrogen peroxide as a predigestion. The predigested samples are then each microwaved for 2.25 minutes. With this procedure, sulfur levels are within an average of 1.27% of that reported for the NBS Citrus Standard, are within 102.25% to 99.44% of the values determined for wet ash digested materials and display recovery rates of 96 to 98% for known levels of sulfur in the range expected in plant foliage.

ISSN:0010-3624    

DOI:10.1080/00103629009368254

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A logistic equation was used to relate dry matter yield to applied nitrogen for Pensacola bahiagrass. Data from Georgia with 5 N rates and for 5 years were used. Procedures were outlined for evaluation of the 3 parameters. The 2nd order Newton‐Raphson method was used to optimize parameters. The error matrix provided estimates of the standard error for each parameter, which were used for sensitivity analysis. Probability contours were constructed for the nonlinear parameters at 75% and 95% confidence levels. Finally, it was shown by analysis of variance that each parameter had a common value for all 5 years of data. Additional work is underway to relate model parameters to water availability and harvest interval.

ISSN:0010-3624    

DOI:10.1080/00103629009368255

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Nitrification in soil is characterized by a sigmoidal curve with a delay, maximum rate and retarded phase. A model based on the Verhulst equation describes all three phases of the nitrification process excellent. Equations to calculate the maximum nitrification rate (Kmx) and the delay period (t') exist already. Equations to calculate the approximate duration (?t) and termination (ts) of the maximal rate phase were also derived from the Verhulst equation and are reported. The duration of maximal nitrification when NH4+is oxidized at a maximal rate is the period from the end of the delay period until the retarded phase starts. The termination of the maximal rate phase gives an approximate time of when the retarded phase, due to a depletion of HH4+, starts. At this stage in the nitrification process additional NH4+must be applied to prevent the minimum changes in the maximum nitrification rate of a soil. When first‐order kinetics is used, the course of nitrification can in future consequently be described quantitatively by four parameters Kmx, t’, ?t and ts. Similar parameters can also be calculated from experimental data of other biological reactions which are characterized by sigmoidal curves.

ISSN:0010-3624    

DOI:10.1080/00103629009368256

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

DTA (differential thermal analysis) was used on mixtures of allophane and imogolite, and a calibration curve for estimating imogolite was obtained using the height of the endothermic peak near 400°C. This peak occurs between 390°C to 430°C, is distinctive and can be used to estimate imogolite in clay fractions and soils. An endothermic peak near 470°C observed in some Andisols probably arises from dehydroxylation of hydrated glass.

ISSN:0010-3624    

DOI:10.1080/00103629009368257

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Iron applications are sometimes used to enhance the color (darker green) of turfgrass stands even when iron is not deficient. A study was conducted to determine the feasibility of replacing a portion of the total yearly N applied to Kentucky bluegrass (Poa pratensisL.) with iron. Turfgrass response to iron chelate (Sequestrene 330) applications at 2.2 kg Fe ha‐1in combination with three liquid‐applied N sources (urea, Formolene, and FLUF) at 25 kg N ha‐1was compared to turf response from applications of the N sources at 49 kg N ha‐l. Iron was substituted for part of the N in either the first and second, second and third, or third application in a four application per year program. The study was conducted for three years, and the fertilized turf was rated for color weekly during the growing season. Depending on N source and frequency of Fe application, turf treated with N received higher color ratings compared to turf receiving Fe + N on 13 (Formolene + Fe in third application) to 36% (Fluf + Fe in first and second application) of the rating dates. Turf color was judged acceptable on 78 to 85% of the rating dates for turf treated with N and 62 to 85% of the rating dates for turf treated with Fe + N. The results indicate that it is feasible to substitute iron for a portion of the N in a urea or Formolene fertilization program but that caution should be used when replacing N from FLUF with iron.

ISSN:0010-3624    

DOI:10.1080/00103629009368258

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor