摘要:

Chemical analyses of feedlot soil profiles showed the presence of high exchangeable K+in the surface of the feedlot profile, which differs greatly from that of adjacent cropland. The K+originated from plant material being fed to the animals. Potassium comprised more than 75 percent of the exchange capacity in this zone. Evidence suggests that K can cause deterioration of the soil physical properties. Low NO3-N below 15 cm demonstrates the lack of water movement through the feedlot surface, the presence of reduced conditions, or both.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Soils representing six great groups were collected from 11 states and Puerto Rico. These soils were selected to provide a broad range in characteristics normally associated with phosphorus adsorption. Regression analysis indicated that aluminum and organic matter in the soil are primarily responsible for phosphorus adsorption. The pH 4.8 NH4OAc extractable aluminum and HCl-NaOH extractable aluminum were particularly useful in accounting for phosphorus adsorption. From the data obtained, it appears that iron probably occupies a secondary role in phosphorus adsorption by soil, becoming important only in local regions where aluminum and/or organic matter content is relatively constant.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The solution Al and exchangeable Al extracted by 0.01 M CaCl2and 1 M KCl, respectively, from the acidic soils of Trinidad were characterized for the hydrolysis products of aluminum ions. The aluminum hydroxide ion product, pAl(OH)3, was found to be independent of solution pH (≥4.0 ≤6.3) when Al(OH)2+, Al(OH)2+, Ale(OH)153+or possibly some other polymer species, and neutral species Al(OH)30were considered as the hydrolysis products. The monomer species Al(OH)2+and Al(OH)2+, and the polymer species, Al6(OH)153+were present in small amounts. The pAl(OH)3values were 34.86 ± 0.16 and 34.77 ± 0.19 for solution Al and exchangeable Al, respectively.The fraction of the total Al present in each hydrolysis species as a function of solution pH was presented graphically. It was found that the predominant species up to pH 4.5 was Al3+, and from pH 4.5 to 6.3 it was the neutral aluminum species Al(OH)30.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A new technique was recently introduced into humic acid chemistry. This involved reaction with phenol leading to depolymerization, and the replacement of aromatic groups by phenol with the formation of relatively simple compounds. These were considered to be characteristic of the linkages joining the aromatic groups together. There is the possibility that reactive groups, other than aromatic ones, could be responsible for the reaction. In this study, reaction of phenol with a range of model compounds is examined so that a further evaluation may be made of the usefulness of phenol depolymerization and to indicate some of the possible side reactions. It is concluded that the overall side reactions are minor and do not invalidate previous conclusions that the phenol depolymerization reaction is useful for the study of humic acid.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Scions of lemon and orange were grafted on sweet orange rootstocks, Citrus sinensis Osbeck “Bessie” grown in fumigated sandy loam. After the plants were well established, half of their number were inoculated with Phytophthora parasitica Dastur and P. citrophthora (Sm. and Sm.) Leonian. Oxygen supply to the root soil environment was controlled by having sealed containers in which oxygen concentrations over the soil surface could be reduced from atmospheric oxygen (20.93 percent) by mixing nitrogen with air. Total dry weights of leaves, stems, and roots were significantly reduced by the presence of Phytophthora spp. while only dry weight of roots was significantly reduced due to low oxygen supply. Even though the dry weight of the lemon tops was greater than that of orange the vigor of the top had no effect on root growth or root rot due to Phytophthora spp.Plants in infested soil had leaves with significantly lower concentrations of P, Ca, Mn, and Fe and significantly higher concentrations of K, Na, and Cl than those from plants grown in noninfested soil. However, supplying oxygen to the root zone at concentrations less than that in air significantly reduced concentrations of N, P, K, Ca, Mg, B, and Fe in leaves. Concentrations of K, Mg, Na, Cl, Zn, and Mn in roots were decreased in the presence of Phytophthora spp., while concentrations of N, P, K, Mg, Na, and Cl in roots were decreased by low oxygen supply. There were significantly higher concentrations of N, K, Ca, Na, Cl, and B in leaves of orange than in leaves of lemon, while in roots of orange there were significantly lower concentrations of Mg, Zn, Mn, and Fe than in lemon roots.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

An experimental study was carried out to clarify the effects of steady and fluctuating non-isothermal conditions on evaporation of homogeneous and structurally layered soil columns.It was found that there were differences in water losses by evaporation caused by the modes of the nonisothermal conditions and by the depth and aggregate size of the top soil layers. Optimal ranges of aggregate size and depth of the top layer were found.Field applications are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Aggregates of two tropical soils from Western Nigeria were used to investigate the possibility of using the raindrop technique to determine the soil erodibility index as compared with soil behavior towards erosion under natural field conditions. Aggregate size, initial soil moisture potential, and raindrop temperature were tested for their effect on structural stability of the soils. High soil moisture potential (more negative) significantly increased the erodibility of a clayey soil containing expanding lattice clay minerals. The erodibility index of a sandy clay loam soil containing kaolinitic clay minerals and amorphous iron and aluminium oxides was slightly decreased when at high moisture potential. The increase in water temperature increased the erodibility of both soils. Erodibility was found to vary directly with sand and inversely with clay content. A routine laboratory method of evaluating the erodibility of a soil using a rating curve is proposed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Recent contributions by J. Císler and J. R. Philip et al. have extended some of the analytical tools developed in the present series of papers on the theory of water movement in soils. Various corrections are discussed and compared in the case of one-dimensional diffusion. It is shown that the suggestion by Cisler to correct my earlier result by simply multiplying it by a constant numerical factor is a significant improvement, particularly when the diffusivity does not vary too rapidly with water content.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The leaf water potential measured on leaf discs with a Wescor (Spanner-type) psychrometer increases with exposure time of the leaf tissue in the psychrometer chamber. A constant value is obtained after 30 to 45 min. The possibility is investigated that these variations reflect an internal equilibration of water potentials within the leaf disc through water movement from the interior of the tissue where the water potential is relatively high at the time of cutting the disc to the surface where the potential in intact plants is relatively low. The psychrometer registers the water potential at an effective surface of the leaf disc. This hypothesis is supported by substantial potential differences that have been reported in the literature and by the qualitative and quantitative agreement of the equilibration pattern with a theoretical model. Various methods of extraction and measurements yielded comparable values for the osmotic potential component.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The slow reactions between phosphate and soil were studied by incubating, at a range of temperatures, soils to which phosphate had been added in solution. After various intervals, solutions which were 0.01 M with respect to calcium chloride, and which contained phosphate, were shaken briefly with the soils and the concentration in equilibrium with the soils was interpolated.The rate of change of phosphate concentration was described by combining the following equation with an adsorption isotherm:dα/dt = k(l — α)nwhere (1 — α) is the proportion of the added phosphate which remains in a form which equilibrates with the solution, k varies with temperature, and n is a coefficient. The effects of temperature were described by the Arrhenius equation and the value of its coefficients were such that a 10° increase in temperature caused an approximately threefold increase in rate. When the temperature was changed during incubation, the rate of reaction changed to a value appropriate to the new temperature. When repeated applications of phosphate were made, the concentration of phosphate was found to be a little higher than predicted on the assumption that the effects were additive. This was attributed to blocking of some of the adsorption sites by the previous additions.While high temperatures accelerated the changes which followed the initial adsorption and thus favored low solution concentration, the effects of temperature on the equilibrium between adsorbed and solution phosphate was found to be in the opposite direction. High temperatures favored high solution concentration—that is, the adsorption was exothermic.When soil was incubated with phosphate it was possible to separate these opposing effects of temperature, but when soil was shaken with phsophate solutions, both effects of temperature were present. The effects of temperature on the changes in solution concentration were therefore smaller when soil was shaken with phosphate than under incubation conditions. On the other hand, the decrease in concentration tended to be faster at a given temperature. This was attributed to effects of shaking in breaking down soil particles.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID