摘要:

Drying of soil samples exposed to high fluxes of air ions of both polarity, produced by corona electrodes, were studied by a beta‐ray gauge. The conventional methods of air‐drying and oven‐drying of soil samples were compared with the new technique. Fluxes of 0.94 x 1012positive and 1.83 x 1012negative air ions cm‐2s‐1reduced drying time of samples by at least three times over the air‐drying controls. Although oven‐drying at a high temperature was the fastest drying method, air ions maintained steady‐state soil temperature during the drying process at 4.5° and 7.3°C below that of the control and ambient temperatures, respectively. There was no significant change in pH, electrical conductivity, and organic matter content values of the dried soil samples of Dalhousie clay, Macdonald sandy loam and St. Sophie sand. Electric wind produced by the ionic drag is proposed to be the principal driving force for the enhancement of evaporation rates from the soil samples. Electroconvection and electrostriction that arise due to the interactions of an external electric field with soil dielectrics may also have contributed to the drying enhancement.

ISSN:0010-3624    

DOI:10.1080/00103628909368150

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Rapid, accurate identification of the lime required to attain a desired pH is essential for the coarse‐textured soils of the Atlantic coastal plain to avoid micronutrient deficiencies (Mn, Zn) in sensitive crops and to insure herbicide efficacy. The University of Delaware Soil Testing laboratory is one of only seven of the 25 states in the Northeastern and Southern regions that does not use a buffer solution to make lime requirement determinations. The present method bases lime recommendations on soil pH in water, combined with an estimate of buffering capacity obtained by hand texturing soils. This approach is time‐consuming and includes the potential for considerable operator variability in obtaining the textural estimate. A study was initiated to compare four buffer solutions (Adams‐Evans, Mehlich, SMP‐single buffer, SMP‐double buffer) with the current approach and the actual lime requirement as determined by incubation of 19 Delaware soils with six rates of CaCO3for six months. Soil pH effects on Mn and Zn availability were determined by extraction of all samples from the incubation study with the Mehlich I (.05MHCl + .0125MH2SO4) soil testing solution. Results indicated that organic matter was the primary soil component responsible for pH buffering in Delaware soils, and that the Adams‐Evans or Mehlich buffers were the best predictors of actual lime requirement. The appropriate target pH range for the coarse‐textured soils of Delaware, based on Mn and Zn availability, was determined to be 5.5–6.0. Liming soils to pH values greater than 6.0 is, for most crops, unnecessary and will reduce Mn availability below critical levels for sensitive crops such as soybeans and small grains.

ISSN:0010-3624    

DOI:10.1080/00103628909368151

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Ferrous sulphate added to potting media based on wood wastes is rapidly rendered insoluble in water. The extractability by DTPA of the added Fe declines over about 7 days to a steady value which is maintained for at least 10 months whether plants are growing in the media or not. The sawdusts and barks tested all required at least 100 mg/L Fe, added as ferrous sulphate, to provide an optimum amount of available Fe; peats needed less Fe and were quite variable in their requirements. In several pot trials, excellent correlations (R20.80–0.86) were obtained between quality or growth of shoots and a combination of medium pH and the concentration of Fe in unbuffered DTPA extractants of concentrations in the range 0.001 to 0.005M, or a saturation extract containing DTPA. Fe concentrations in DTPA/TEA/CaCl2, NaHCO3/DTPA, 0.5M ammonium acetate solutions and water were less precise indicators of Fe availability. At media pH values of 5.5–6.0. 0.002M DTPA (1:1.5 volume) extracts need to contain at least 20 mg/L Fe and preferably 30 mg/L Fe for adequate Fe supply if ferrous sulphate is the source of added Fe. Some species need at least 40 mg/L Fe or must be grown at a lower pH. These criteria do not hold if the main source of Fe is FeEDDHA.

ISSN:0010-3624    

DOI:10.1080/00103628909368152

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

There has been strong support for the hypothesis that the adverse effects of plant residues on crop yields are due to phytotoxic compounds derived from these residues. This hypothesis is based largely on studies showing that, when compared with distilled water, aqueous extracts of plant residues have an adverse effect on seed germination and seedling growth. Because seed germination and seedling growth are reduced by a delay in germination resulting from slow uptake of water by seeds, we studied the possibility that the adverse effects of aqueous extracts of plant residues on seed germination and seedling growth might be at least partly due to water uptake by seeds being retarded by water‐soluble constituents of these residues. To test this possibility, we compared the rates of water uptake and germination of seeds of corn(Zea maysL.), soybean[Glycine max.(L.) Merrill], and wheat(Triticum aestivumL.) when these seeds were treated with distilled water and with aqueous extracts of corn, sorghum [Sorghum bicolor(L.) Moench], and wheat residues. We found that the rates of water uptake and germination of seeds treated with aqueous extracts of plant residues were appreciably slower than the corresponding rates for seeds treated with distilled water. This may be due to the water potentials of these extracts (ca. ‐50 kPa) because when seeds of corn, sorghum, and wheat were treated with a solution of polyethylene glycol 8000 having a water potential similar to that of the extracts of plant residues tested, the rates of water uptake and germination were also slower than the corresponding rates for seeds treated with distilled water. These observations suggest that the adverse effects of aqueous extracts of plant residues on seed germination and seedling growth when compared with distilled water may be partly due to constituents of these extracts inducing water potential effects that reduce water uptake by germinating seeds.

ISSN:0010-3624    

DOI:10.1080/00103628909368153

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Previously employed urea hydrolysis method (4) for the determination urease activity on phylloplanes fails if pre‐applied urea is present as a residue from fertilizer, urine or other sources prior to assay. Under such conditions the total urease activity is underestimated and the extracellular component is overestimated. A modified method is proposed that employs an additional measurement where mercuric chloride is a component of the assay incubating medium, which enables a correction to be made to urease activities estimated under such conditions. However, where no urea is present prior to the assay, previously employed methods are acceptable. Using the proposed modifications, urease activities on the phylloplane which had received urea dressings previously were shown to be depressed over the following 2 or 3 days due to the presence of ammonium ions.

ISSN:0010-3624    

DOI:10.1080/00103628909368154

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Five representative soils with contrasting physical, chemical, and mineralogical characteristics from the Chaouia and Gharb regions of northwestern Morocco were selected for a study of the effects of wetting and drying cycles (W‐D), temperature, amount of K+added, and extracting solution on the determination of K‐fixation. With drying at 40°C and the use of of 0.2 M CaCl2for K+extractions, the measured amount of K+fixed increased with increased number of W‐D cycles when high quantities of Kwereadded. The drying, however, caused release of K+when no or small amounts of K+were added even for soils not containing mica (illite). With 2 W‐D cycles, measured K+fixation decreased with increasing drying temperature from 40oC to 100oC regardless of the extracting solution when the calculated fixation was based on the initial extractable K+rather than the quantity extracted from the zero treatment after wetting and drying. Also, significant differences in K+fixation existed between extracting solutions at any given temperature. Because of the different drying temperatures and extracting salts used it is difficult to compare results of K+fixation reported in different studies. Frequent changes in temperature and soil water content during the growing season in Mediterranean climates may have an important influence on K+availability.

ISSN:0010-3624    

DOI:10.1080/00103628909368155

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The acidulation effects of the prolonged use of nitrogenous fertilizers on selected chemical and microbiological properties of a silt loam soil (Typic Ochraqualf) were assessed.

ISSN:0010-3624    

DOI:10.1080/00103628909368156

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Concentration of P in ear leaf samples at silking is widely used to detect P deficiency in maize. Ear leaf P concentration failed to indicate P deficiencies that were indicated by P concentration in shoots at the 4‐ to 6‐leaf stage in a field study in Ontario, Canada. To determine which samples were a better indicator of P deficiency, plant analysis data from Ontario field studies in which grain yield responded to P were interpreted using sufficiency ranges and DRIS methods. Ear leaf P concentration and P index usually failed to detect P deficiency and were only slightly affected by P fertilization. For shoots at the 4‐ to 6‐leaf stage, P concentration and P index usually correctly detected P deficiencies. Concentration of P and P index values for seedling shoots changed rapidly during early growth, resulting in diagnoses that varied with sampling time. The ear leaf at silking should be disregarded as an indicator of P deficiency for maize in Ontario. Reliable methods of assessing P nutrition of maize during early growth need to be developed.

ISSN:0010-3624    

DOI:10.1080/00103628909368157

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Long‐term effects of alternate tillage systems on soil‐test values for Coastal Plain soils were unknown. Therefore, soil pH, organic carbon, and Mehlich I extractable P, K, Ca, and Mg concentrations measured during an eight‐year tillage study on Norfolk loamy sand (fine‐loamy, silicious, thermic, Typic Paleudults) have been summarized. Yields for corn(Zea maysL.), wheat(Triticum aestivumL.), and soybean[Glycine max(L.) Merr.] are also summarized to provide an indication of nutrient removal by the crops. Soil‐test measurements after six years showed no significant differences in Mehlich I extractable nutrient concentrations for the 0‐ to 20‐cm depth between disked (conventional) and nondlsked (conservation) tillage treatments, but for pH, P, Ca, and Mg, the tillage by depth of sampling interaction was significant at P‐0.05. Stratification did not appear to affect crop yield. Soil organic matter concentration in the Ap horizon nearly doubled after eight years of research at this site. This change occurred within both tillage treatments, apparently because high levels of management produced good crop yields, residues were not removed, and even for the disked treatment, surface tillage was not excessive. These results show that long‐term average yields for corn and soybean on Norfolk soil will not be reduced by adopting reduced or conservation tillage practices. They also show that nutrient levels can be maintained at adequate levels for crop production on Coastal Plain soils by using current soil‐test procedures and recommendations for lime and fertilizer application.

ISSN:0010-3624    

DOI:10.1080/00103628909368158

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Lime requirements ordinarily are based on buffer methods but could be based on unbuffered salt‐exchangeable acidity. The relationships between exchangeable acidity (EA) and buffer acidity (BA) were studied across a range of pH levels established through lime trials in four Ultisols and one Histisol in North Carolina Coastal Plain and Piedmont regions. Buffer acidity was proportionately higher than EA in all soils at any pH level. Linear regression slopes between either BA or EA and pH, within each soil, were not significantly different when the latter relationship included samples with pH less than or equal to 5.4. Variations in EA accounted for by BA ranged from 41 to 67% among the soils investigated. Buffer acidity alone accounted for 64% of the variation in EA for samples from all soils with pH less than or equal to 5.4. Including a squared BA term and either HM or CEC increased the R2to 0.79 and 0.86, respectively, but neither equation provided a completely suitable prediction of EA across all five soils investigated.

ISSN:0010-3624    

DOI:10.1080/00103628909368159

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor