摘要:

The induced periodic changes in &thetas; at the various soil depths, and the analogy of the soil water regime during infiltration under a pulsed water application to a wave propagation phenomenon was formulated and experimentally tested. The time changes in &thetas; at a number of depths in soil columns receiving water under two pulsation regimes were well represented by a Fourier series. The computed amplitudes of the &thetas; time changes,Cn,z,were damped exponentially with depth, and the computed phase shifts &phis;n,z,increased linearly with depth, as expected by theory. A similar behavior was observed with the experimentally determined amplitudes. Under the higherRiandRavvalues, however, no damping of the amplitude was observed at a soil depth range of 0.5–3.5 cm.Representative damping depths of 4–5 cm and 9–11 cm were obtained for the soil columns receiving water atRavvalues of 1.0 mm/hr, respectively, for a period of 60 min. When periodic water pulses are applied at the soil surface, the induced time fluctuations in &thetas; andqare exponentially damped with depth. Below the damping depth the water pulses applied at the soil surface are stretched almost evenly throughout the period. As a result the volumetric soil water content is constant with time and depth at a value determined by the time-averaged application rate,Rav.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Soil air pressure and surface water head were measured at a single field site during eight irrigations of alfalfa during the 1972 growing season. Soil air pressurehsand surface water headhware presented as functions of elapsed irrigation time to illustrate the short-term and seasonal variation of these parameters. It is shown thathavaries directly withhw,and that the head imbalanceha-hwincreased at a decreasing rate during each irrigation, until it reached a plateau ranging between 4 and 7 cm, and therefore, it remained nearly constant until headgate closure. Small differences inha–hwbetween irrigations may have had a significant effect on infiltration because total field application decreased asha–hwincreased. Soil air pressure increased under simulated rain when ponding began where airflow was restricted by an impermeable barrier at a 20-cm depth. This air pressure increase had little apparent effect on infiltration. Soil air pressure created and maintained from the onset of infiltration reduced infiltration by about 20 percent.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

A numerical method for the simulation of unsteady ground-water flow is presented. In order to treat soils that are both saturated and unsaturated, stiffly stable, multiple-value methods with automatic control of order and step size are used. Numerical results from some model calculations are given.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

In a greenhouse experiment corn plants were harvested 24 and 31 days following emergence from pots containing Bloomfield loamy sand (Psammentic Hapladalf). The soil CEC was 2.3 meq/100 g. The soil had 140 kg/ha of P determined with the Bray P1extractant, and 220 kg/ha of 1Nneutral ammonium acetate extractable K. Calcium, Mg, K, and P concentrations in plant tissue were determined by emission spectroscopy. Treatment combinations were a factorial arrangement of 0, 2.5, and 5 ±/g of Cd and 0, 125, and 250 ±/g of Pb.At 24 days following emergence, there were significant main effects of Cd and Pb upon the Ca, Mg, K, and P concentration in corn plants. The Cd linear × Pb linear interaction significantly (α = .05) affected P concentration and uptake of each element.At 31 days following emergence, Cd and Pb main effects influenced the Ca, Mg, and K status of the plant, but had no significant effect upon P content. At this stage of development, there were three significant Cd-Pb interactions that affected nutrient concentration and four interactions that affected nutrient uptake.Results observed in this study suggest that the statistical significance of various effects depends upon stage of development of the corn plant, and that certain Cd-Pb interactions influenced nutrient concentration in the plant.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Nondestructive neutron activation analyses were made of 43 samples representing different Bulgarian soils. As many as 19 trace elements were determined by nondestructive, high-resolution, gamma ray spectrometry of the nurtron-irradiated samples. The use of a low-energy photon spectrometer detector “LEPS” permitted the determination of some elements that cannot be detected with a standard type GeLi detector.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Seventy-one aseptically collected soil samples from Australia, Fiji, Moorea, Malaysia, New-Zealand, American Samoa, and Tahiti were assayed for the occurrence of soil algae by the technique of enrichment culture. Representatives of 5 genera of blue-green algae and of 24 genera of green algae together withEuglenaand 4 Xanthophycean algae were encountered. Species ofChlamydomonasandChlorococcumproved to be the most ubiquitous, withTetracystisandChlorosarcinopsisoccurring in approximately half as many samples. The morphology and reproduction ofPseudotetraëdron polymorphum(Chlorophycophyta, Chlorococcales, Chlorococcaceae), a genus and species new to science, are described and illustrated.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The addition of montmorillonite accelerated CO2production and O2consumption of soils enriched with various aldehydes (benzaldehyde, syringaldehyde, vanillin,p-dimethylaminobenzaldehyde, heptaldehyde, acetaldehyde). This acceleration was observed both in freshly prepared soil-montmorillonite mixtures and in mixtures prepared more than 3 yr before use. The addition of kaolinite or mica-vermiculite did not affect the rate of aldehyde degradation in soil. Possible mechanisms whereby montmorillonite influences the decomposition of aldehydes in soil are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The design, construction, and application of an inexpensive, mercury-pressure control device, designed for use in combination with the constant vacuum, porous cup, soil-solution sampler, are given. This unit has the capability to shut off the constant pressure source when a predetermined volume of water has been collected. The newly designed assembly inherits all the advantages of the original design, and eliminates the contamination resulting from overfilling of sample bottles and the influence of soil volume.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Weight loss, reduction of tensile strength, and carbon dioxide evolution indicate that polybutene film-mulch, partially photodegraded by sunlight, is slowly degraded and mineralized by microorganisms in soil. As judged by weight loss, no biodegradation of film-mulch previously unexposed to sunlight occurred under similar conditions, although tensile strength eventually declined. These findings are consistent with the theory that free radical reactions promoted by sunlight create short polybutene chains with polar end and side groups that are susceptible to subsequent microbial attack. No microbial growth on the partially photodegraded polybutene film as a sole source of carbon could be demonstrated, and degradation is believed to occur by cometabolism. Controlled photodegradation and subsequent biodegradation lead to postharvest disintegration and recycling of the film-mulch, thus eliminating an environmental pollution problem without costly collection and disposal processes.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Discontinuous boundary or initial conditions introduce singularities in the solution of the diffusion equation. Numerical techniques cannot describe such singularities exactly. Hence, it is important to be able to evaluate a priori the error of the numerical approximation near singularities. It is proposed here that an exact solution with both spatial and temporal singularities can be used to assess the precision of the numerical approach. This assessment carried out for a particular case can be used to give an indication of the validity of the numerical technique for more general problems when no exact solution is available.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID