摘要:

Flow through the xylem of a complex root system is simulated to measure xylem resistance to water flow, and to determine whether or not this resistance is significant. Equations are set up that model xylem water flow as if it were flow through thin tubes. The root characteristics needed to solve these equations are obtained from an earlier work.Xylem water flow is first considered for a single main root and its laterals. It decreases with age of the root or increase of root length, and it increases with the addition of laterals. The advantage of an increasing number of main roots is also shown. Finally, flow through the plant crown is compared to Thornthwaite and Blaney-Criddle evapotranspirational estimates. Less than 10 millibars of water pressure is needed to overcome xylem resistance, and, therefore, the resistance is considered negligible.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Surface tensions of the following solutions were measured: (a) fulvic acid (FA) and humic acid (HA) at various pH and concentration levels; (b) FAs and HAs from widely differing origins; (c) pyrolyzed FA; (d) leaf extracts; and (e) saturated soil extracts.Both FA and HA solutions lowered the surface tension of water significantly. The surface tension of HA solutions decreased almost linearly with increasing concentration, whereas a surface tension vs. concentration plot for FA had a hyperbolic shape. Surface tensions of HA and FA solutions also decreased with increase in pH. The lowest surface tensions measured were 43.2 and 44.2 dynes/cm for FA (at pH 12.0, 3 percent w/v) and HA (at pH 12.7, 2 percent w/v), respectively. The surface tension of water is 72.0 dynes/cm at the same temperature and pressure. Numbers of molecules per 100Å2of liquid-gas interface were 1.04 and 2.47 for FA and HA, respectively. Surface tensions of FA and HA solutions at pH 7 (0.6 percent w/v), prepared from humic materials from widely differing origins ranged from 46.1 to 69.2 dynes/cm. Pyrolyzed FA, which had lost its functional groups, lowered the surface tension of water only slightly. The total acidity of the FAs and HAs showed a linear, inverse, significant correlation with surface tension. Leaf extracts depressed the surface tension more than did saturated soil extracts. From the results it appears that if there is a deficiency of FA in the soil solution, water repellence will result; but if there is an ample supply of FA, soil wettability increases.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The behavior of sulfate concentration in the leachate of an acid podzolic brown earth was studied, when a slug of neutral salt (KCl + KNO3) passed through the upper sulfate-enriched layers of the soil. The effluent of five undisturbed soil columns was collected daily, and H+, Cl-, and SO4–concentrations were measured. A constant flux of water, either 1.0 cm/day or 0.3 cm/day, was maintained. Sulfate concentration in the leachate showed a decrease when the salt passed the columns. The decrease corresponded with an increase of H+and Cl-concentrations. The behavior of sulfate was almost the same irrespective of the flow rates. At the lower rate, sulfate retention was about twice that at the higher rate. Though precipitation of basic aluminum sulfates cannot be excluded, the behavior of sulfate must be interpreted in terms of specific adsorption.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Soils of two oil palm (Elaeis guineensis) plantations were studied for their bacteria and yeast composition.The pH and moisture and organic matter content of the soils were determined in addition to their mechanical composition. Population counts of the two organisms were done using both the dilution method and the direct-plate-count method at four times of the year (October, December, March, and July).Twelve bacteria and thirteen yeast species were isolated during the investigation. The lowest population figures were obtained during the period of the year with high temperatures and no rainfall. Soil samples from water-logged areas contained low yeast and bacteria populations.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

A study was conducted to determine the status of phytotoxic aluminum in soil by means of titrating reactive soil aluminum with fluoride using a fluoride-ion-selective electrode. Fluoride-titratible aluminum was compared with 1NKCl “exchangeable” aluminum in soil samples from Brazil and kaolin clay with and without added aluminum.Monon wheat plants were grown in soils with different levels of reactive aluminum as characterized by fluoride titration. Plant yield, as determined by dry weight, decreased significantly with increasing quantities of fluoride-titratible aluminum.The fluoride-titratible aluminum was more closely correlated with plant growth than was KCl-extractable aluminum, and the titration procedure has potential for defining the nature and type of phytotoxic aluminum in soil.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

An experiment was conducted on a sandy loam Alagba soil in southern Nigeria to obtain information on the effectiveness of methods of applying P fertilizers on soils of the humid tropics. Phosphorus rates ranging from no phosphate applied to 256 kg P per hectare applied, and percentage of the soil volume fertilized, ranging from banding to 100 percent incorporation in the surface (0–15 cm) soil volume, were tested in factorial combinations using a continuous function experimental design.Response to P fertilization was greatest during early growth and decreased with advanced maturity. External P requirements at 3, 6, and 9 weeks of growth were estimated at about 6, 0.02, and 0.001 μg P/ml, respectively. A rather low soil solution concentration of 0.01 μg P/ml was associated with 95 percent of maximum grain yield, which may be related to the low yield level realized.Advantages of localized P placement were observed only at suboptimal P rates. With an adequate rate of fertilization, the best results were obtained from incorporating P in the entire cultivated soil volume. This study did not support the idea sometimes put forward that major economies in fertilizer use can be achieved as a result of localized placement of phosphate fertilizer.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Trifluralin (α, α, α-trifluoro-2, 4, dinitro-N, N-dipropyl-p-toluidine) was applied in 1973 to Egam loam and Beason clay field plots, which differed in slope and texture of the surface 12 in. of soil. Recommended (1×) and excessive (1.5× and 2×) rates of trifluralin were applied, and the herbicide was incorporated to a depth of 4 in. Movement of trifluralin below the 8-in. depth was essentially nil in both soils, but considerable movement occurred to the 8-in. depth in both. Trifluralin longevity in each soil was essentially the same, although higher rates were applied in the clay soil. On the average, less than 1% of the herbicide remained 5 months after application; an increasing trend of trifluralin residues with 1.5× and 2× rates was discerned, however. No herbicide was found in the soil the following spring (11 months after application). There was some evidence of upward movement of trifluralin in both soils.Trifluralin degradation followed first-order kinetics with half-life values of 35.8 and 25.7 days for Egam and Beason soils, respectively.Five weeks after herbicide application, control of two broad-leaf weeds and one grass weed was poor, being consistent with low herbicide concentrations (0.06 ppm) remaining in the soil at that time. The growth of oats (Avena sativaL.), a species sensitive to trifluralin, was also not significantly affected in the greenhouse at 0.05 ppm of trifluralin concentration.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

The sodium-bicarbonate (NaHCO3) method of Olsen et al. was primarily designed to extract inorganic P (P1) and to correlate this P-pool with plant response. This procedure was used to follow the transformations of organic P (P0) substrates in soil. Various commercial P0substrates were added to a sandy loam soil, and were extracted immediately and after 1 to 18 days of incubation at field capacity. Glycerophosphate and all 3‘ nucleotide components of RNA were completely mineralized and accounted for in the NaHCO3solution after 3 days. While RNA degraded in 18 days, sodium inositol hexaphosphate (Na-phytate) was relatively unaffected during this time and unrecoverable in the NaHCO3solution upon immediate extraction. Thus, the labile compounds, like RNA, its four 3’ nucleotides, and glycerophosphates were recoverable in the 0.5-MNaHCO3-extracting solution (pH 8.5) of Olsen et al., while the Na-phytate, a relatively resistant compound, was not. Native P0was only slightly affected, however. A relatively constant amount of native P0was extracted, irrespective of extraction periods lasting 0.5 to 6 h.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

ZnSO4, Zn EDTA, ZnS, and ZnSO4plus NH4H2PO4were banded in soils, and the solid-phase zinc compounds were identified using x-ray diffraction analysis. Solubility of zinc in soil adjacent to the fertilizer band was determined by measuring the zinc concentration in soil-water extracts.The reaction product in a noncalcareous soil (pH 8.2) treated with ZnSO4was Zn(OH)2, which was metastable and persisted for only a few weeks. ZnSO4was usually precipitated as ZnCO3and Zn5(CO3)2(OH)6in the calcareous soils. No crystalline reaction products were detected in soils treated with Zn EDTA. ZnS was usually identified in soils treated with ZnS. In addition, Zn5(CO3)2(OH)6and Ca[Zn(OH)3]2$2H2O were found in a calcareous soil treated with ZnS and incubated for 32 weeks. Reaction products formed when ZnSO4plus NH4H2PO4was added in a band were Zn3(PO4)2$4H2O in the noncalcareous Newdale soil and Zn3(PO4)2$4H2O, NH4ZnPO4, and ZnCo3in the calcareous Lakeland soil.Concentrations of zinc in water extracts of soils treated with zinc were greater than in untreated soils. Zinc concentration in water extracts of soils was greatest with Zn EDTA and lowest with ZnS. Zinc concentration in water extracts of calcareous soils was less than in noncalcareous soils treated with ZnSO4. Zn EDTA was highly soluble in all soils. Zinc concentration decreased with time of incubation in soils treated with ZnSO4or Zn EDTA, but zinc concentration of water extracts increased with time in soils treated with ZnS. Zinc concentration in water extracts of soils treated with phosphate plus ZnSO4was less than for soils treated only with ZnSO4.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID