摘要:

An accurate, two-term solution of Richards' equation for one-dimensional, vertical infiltration was obtained by a finite difference, iterative method (FINDIT). Wetting distances and soil water content distributions closely resemble those obtained by Philip with his series solution, which is extremely accurate at short times but fails to converge for long times. Solutions appear to be equally accurate for all times using the proposed procedure. Hence, the proposed procedure does not require additional approximations or matching factors to link separate analyses for short or long infiltration times. Because the solution equation consists of only two terms, the inflow is logically partitioned into matric and gravitational components. The matric component is expressed in a constant sorptivity termS, conceptually identical to the sorptivitySof Philip. The gravitational component is time-dependent and increases to a maximum value equal to the hydraulic conductivity at the soil surface as time approaches infinity. After appropriate coefficients have been determined, both matric and gravitational components of cumulative infiltration may be expressed independently by a logarithmic relationship that avoids the use ofDandKfunctions and iterative computer procedures.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

This study was conducted to characterize the extractability and solubility of phosphate in soils amended with anaerobically digested sewage sludges that resulted from treatment of sewage with Ca(OH)2, Al2(SO4)3, or FeCl3. The sludges were applied annually to field plots situated on a loamy sand (pH 7.3) and a loam (pH 7.4) and cropped to corn (Zea maysL.) or bromegrass (Bromus inermissLeyess) for 7 years. Extractability of soil P by NaHCO3was in the order Ca-sludge ≫ Fe-sludge ≥ Alsludge. Equilibrium P concentration was highest in the loam treated with Ca-sludge and in the loamy sand treated with Fe-sludge. The solubility of P in Ca-sludge-amended soil appears to be limited by the precipitation of octacalcium phosphate. The Fe-sludge decreased soil pH, and this increased P solubility. Soil Fe and Al oxide content was increased by sludge application; this increased P retention in soil through sorption and occlusion by the oxides. Calcite in the Ca-sludge-amended soil provided additional sorption sites. Fractionation of soil P showed that just over 50 percent of inorganic P in the Ca-sludge treatment and about 70 percent in the Al- and Fe-sludge treatments were Al- plus Fe-P. The relatively high Al- plus Fe-P in the Ca-sludge treatment resulted from the use in 1977 of a sludge treated with Ca and Fe. More P was present as loosely bound P (NH4Cl-extractable) and as a Ca-P in the Ca-sludge treatment than in Al- and Fe-sludge treatments.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Columns of three sandy soils were leached with water after surface applications of diammonium phosphate (DAP) or with solutions containing DAP. Final concentrations of Bray and Kurtz extractable P and, for two soils, exchangeable K were measured. Substantial amounts of P and K were leached downward. Where large amounts of water were applied and DAP was added in dry form, some native P was removed from all soils. For the most part, the P distribution patterns were similar for the three soils, but the magnitude of effects of P and water (solution) rate varied. Generally, the amount of P extracted was linearly related to the amount of applied P, whereas it was curvilinearly related to the amount of applied water. Large amounts of K were leached through columns of one soil. The amount of extractable K remaining in the column was linearly related to P applied and logarithmically related to the amount of water (solution) applied.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We grew wheat in sand culture to evaluate the effects and interactions among levels of δ-MnO2, CaCO3, and added Mn2+and Fe2+on yield and chemical composition of the crop. The experimental variables, at five levels each, were arranged in an incomplete factorial combination for response surface evaluation.Treatment effects on yield were not statistically significant, although the plants growing in unlimed pots were stunted and presented symptoms of Mn toxicity.The concentration of Mn in plant tops varied from 78 to 6140 ppm. Over 90% of the variation in Mn uptake was explained by the levels of Mn2+, CaCO3, and δ-MnO2, and by some of their quadratic and interaction terms. Calcium carbonate had a strong negative effect on the uptake of Mn, attributable to immobilization of the divalent cation through adsorption and precipitation, or formation of manganocalcite. Although δ-MnO2was a source of Mn to plants at low levels of added Mn2+, it presented a negative influence at high Mn2+levels because of adsorption and oxidation of Mn2+on its surface. Added Fe2+did not significantly influence Mn uptake. The significant interactions, δ-MnO2X Mn2+and CaCO3X Mn2+, were negative, indicating that the response to added Mn2+was depressed by the presence of δ-MnO2and CaCO3, both buffers of Mn2+concentration.None of the factors studied influenced plant uptake of Fe. The concentration of Fe in plant tissues varied from 34 to 54 ppm, except for those of the no-line treatment, which contained 108 ppm. These results were attributed to sorption and oxidation of Fe2+on the δ-MnO2surface at all levels of added oxide, both reactions being favored by high pH.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

We conducted experiments designed to determine if soil aeration could be improved and if the oxygen stress brought about by flooding could be reduced by addition of peroxide to the soil-root medium. Tomato plants (Lycopersicon esculentumMill.) growing in containers filled with a potting mix of peat moss and sand were subjected to combinations of treatments with and without flooding and peroxide additions. Aeration status of soil mixes during the study was measured with platinum microelectrodes for redox potentials (EH7) and oxygen diffusion rates (ODR). Plant heights were measured at weekly intervals, and shoots were harvested for fresh and dry weights. The growth of tomato plants watered as required was not increased by peroxide fertilization. Plants that were flooded, however, did grow significantly better when peroxide was included in either the flooding solution or the watering solution after flooding. Redox potential measurements, taken after 48 hours flooding, were below the value of 320 to 340 mV, at which point oxygen becomes depleted from soil. The high ODR values indicated good oxygen availability in the mix prior to the first flooding and prior to harvesting.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Rhizobia inoculated on leguminous seeds are often exposed to adverse environmental conditions, which affects survival and subsequent effectiveness. Studies were performed to examine the effects of temperature-moisture stress on rhizobia inoculated on seeds in peat-base and oil-base inoculants. Plate count and most-probable-number analyses were used to determine the survival of rhizobia on seeds planted in dry sand at specific sampling times. Plants were grown from inoculated seeds after exposure to 16 days of temperature-moisture stress to assess nodulation and plant growth. For bean seeds that were inoculated with 107cells ofRhizobium phaseoli931A, 3.0 X 106cells/seed (plate counts) were recovered from seeds inoculated with the oil-base carrier, compared with 8.0 X 102/seed with peat-base inoculant. Oil-base inoculants, in this instance, promoted higher survival of rhizobia on seed than did peat-base inoculants. Plants inoculated with oil-base inoculants had higher nodule numbers and weights than plants inoculated with peat-base inoculants. Shoot dry weights and total nitrogen content were likewise increased with oil-base inoculants. Results suggest that oil-base inoculants may provide more protection than peat-base inoculants when rhizobia are inoculated on seeds and exposed to conditions of drought and high temperature.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

In this study, we sought to determine the effect of low-level nitrogen fertilization in the rejuvenation of old stands of crested wheatgrass [Agropyron desertorum(Fisch. ex Link) Schult.] to increase dry matter production. Spring and fall applications of 0, 22, and 34 kilograms N/hectare were evaluated for their effect on total dry matter (TDM) production, crude protein concentration, and water use efficiency (WUE). Fertilizer treatment effects on the TDM and crude protein of the forage were very erratic and inconsistent. Nitrogen analysis of plant litter and soil showed significantly more residual N on the fertilizer treatments, compared with the control, but the N was apparently immobilized. These low-level fertilizer applications of 22 and 34 kg N/ha appeared to be too low for crested wheatgrass rejuvenation under the conditions of this study.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

In a field study, we investigated the effect of seed-bed preparation methods and mulch materials on soil temperature. Seed-bed preparation methods involved ridges and flat surfaces, and mulch materials were rice straw and clear plastic sheets used on flat surfaces.In ridges 1 cm deep, the maximum soil temperature was 6°C higher and the minimum was 2.5°C lower than that observed in a flat plot. Plastic mulch on a flat surface lowered the maximum temperature at the 1-cm depth by 5°C, and rice straw mulch lowered it by 16°C, compared with bare flat. These differences decreased with depth. Regression equations between soil depth and the differential of the maximum or the minimum soil temperature at any depth and corresponding air temperature 1 m above ground level were developed. The correlation coefficients varied between 0.98 and 0.99. The soil temperature computed from the regression equations utilizing air temperature was in good agreement with the observed. Fourier series analyses of soil temperature showed that the first two harmonics could describe the temperature at the 5-cm depth satisfactorily and that the first harmonic alone could do so at the 35-cm depth.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Water desorption and mercury intrusion methods were used to characterize the pore size distribution of a sand, and the hydraulic conductivity-water content function,K(ø), was calculated therefrom. When used as input to an infiltration simulation model, theK(ø) function obtained from the water desorption method resulted in a better prediction of the actual wetting profiles than did theK(ø) from mercury intrusion. However, the results of the latter method could be made to match those of the former by use of an empirical correction factor. It appears, therefore, that the mercury intrusion method, which offers the advantage of rapidity, can be helpful in characterizing soil hydraulic behavior only if its results are appropriately adjusted.

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1982

数据来源: OVID