摘要:

SummaryA model of solute uptake by a growing root system is discussed in relation to the ability of a soil to support the nutritional requirements of plants. It is quantitative, and should apply to the absorption of nitrate, phosphate, and potassium by grasses and arable crops. The principles, if not the detail, are relevant to all soils.The model was tested in an experiment in which the nitrogen and potassium taken up by a rape plant were measured. The results suggest that the model has identified the significant variables in the absorption process.The principal factors affecting the supply of nutrient to a given plant are the total quantity of diffusible nutrient, the rate at which the nutrient can move, and the distance it has to travel to a root surface. The exact relevance of each factor for the different nutrients is readily determined.The diffusion coefficients of potassium and phosphate are often low. Mass flow contributes little to their supply, and an adequate exploitation of the soil reserves depends on a well‐developed root system. Nitrate, on the other hand, can usually move easily to roots, either by diffusion or mass flow. The whole rooting volume is depleted fairly quickly, and the amount absorbed depends solely on the quantity present in the rooting volume.These ideas have practical significance. In particular, they suggest that the soil properties which influence root growth may deserve as much attention as soil chemical composition in the drawing up of fertilizer recommendation

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01943.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryEffects of acid pre‐treatment and fractionation on the molecular weight distribution of OIM Na4P2O7organic matter extracts were investigated in a chronosequence of weakly weathered soils developed on aeolian sand in New Zealand.Acid pre‐treatment of soils with OIM HCl followed by OIM HCI:03M HF was found to enhance the polydispersion in the nominal molecular weights of the extracts. The same treatment resulted in significant increases in yield and reduction in ash content. However, prolonged standing of extracts in the acids led to acid‐induced polymerization, resulting in a predominance of organic matter in the higher nominal molecular weight ranges.Fractionation of organic matter extracts by acid precipitation into humic and fulvic acids did not separate them according to molecular weight as commonly believed. Instead, fulvic acids from most soils were found to have similar nominal molecular weight distributions to those of their humic acid counterparts. A large proportion of soil fulvic acid compounds was in the>100 000 nominal molecular weight

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01944.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryA soil profile is considered as the result of the interaction of pedogenic and gradational processes. Distinction is made between monopedomorphic, polypedomorphic, and buried soils. Description of these soils often meets with difficulties due to inadequacies in existing profile description systems. A new system is proposed, based on the differentiation between gradational and pedomorphic features. In this system the concept of pedogenetic horizons (A, B, C, etc.) is deliberately abandoned in favour of the recognition or failure to recognize pedomorphic features at a certain depth and over a certain vertical extent. Some examples serve to elucidate the new system.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01945.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe drop‐cone method, in which a 30° cone of mass 80 g is allowed to sink into a soil sample at a selection of moisture contents, is described and examined as a possible alternative to the Casagrande device for liquid limit determination. The methods are compared for 13 arable topsoils. The drop‐cone method, which uses apparatus that is readily available commercially, is shown to have advantages in ease of conduct of the test and in greatly improved reproducibility between opera

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01946.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryPhosphate sorption data for twenty‐nine soils were found to fit the Freundlich adsorption isotherm better if a measure of native labile P was first added to the sorption data, and this sum plotted against intensity. The exponent from the isotherm thus obtained was closely related to exchangeable A1 (in acid soils) and exchangeable Ca (in neutral and calcareous soils), with a mole ratio of one P to 6 A1 or C

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01947.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryA technique to study optically the effects of three different extraction procedures for removing iron from thin sections of soil is described. The distribution of iron in each section is recorded before treatment. Silicone grease is then applied to all parts of the sections except those to be treated. The areas selected for treatment are immersed for 24 hours in one of three beakers containing dithionite‐citrate‐bicarbonate, 02M ammonium oxalate at pH3and 01M K‐pyrophosphate at pH10. After treatment, the sections are degreased and the effects of the various treatments examined opti

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01948.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryPhosphate was adsorbed at a constant pH, on allophane clay samples which had been pre‐treated with selenite to remove adsorbed silicate. The concomitant release of selenium, silicon, and hydroxyl ion on phosphate adsorption was also measured. The results are compared with those obtained from a similar experiment conducted using clay which had not been treated and they substantiate the earlier conclusion that phosphate displaces structural silicon of clays. The amount displaced increases parabolically with increasing levels of phosphate adsorbed over the concentration range studie

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01949.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryPhosphate adsorption isotherms were determined for four synthetic amorphous aluminosilicate gels with A1: A1 + Si molar ratios of 0.29 to 0.88. The concomitant silicate release and acid consumed to maintain the pH of the suspensions constant were also measured.The adsorption isotherms were analysed applying a two‐term Langmuir equation–assuming two types of sites. The experimental points fitted the predicted adsorption curves only up to a certain amount of phosphate adsorbed. The deviation at high phosphate adsorption values suggested the presence of more than two types of adsorption site.A comparison of phosphate adsorbed with the silicate released and acid consumed to maintain the pH constant indicated that, for a 3 h reaction time at concentrations below about 10 μmol cm−3, phosphate exchanges mainly with aquo and hydroxo ligands and with adsorbed silicate. At higher concentrations phosphate is adsorbed (i) on sites arising from the disruption of hydroxy aluminium polymers in the gels and (ii) by the displacement of structural si

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01950.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe apparent bulk phosphate self‐diffusion coefficient, resin extractable and isotopically exchangeable phosphate were measured on an acid Cecil sandy loam soil pre‐treated with calcium carbonate and monocalcium phosphate. Apparent diffusion coefficients increased four‐fold with a five‐fold increase in phosphate addition, but were not increased by liming. Resin extractable phosphate was greater than isotopically exchangeable after large phosphate additions. Calculated porous self‐diffusion coefficients did not change as a result of phosphate additions. The contribution of solid‐phase phosphate to diffusion was small and close to the limits of

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01951.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SummaryThe study was designed to obtain information on flow and salinity of the groundwater, and on moisture regimes above the water table at selected sites near Vegreville, Alberta, and to relate this information to features of soil genesis revealed by soil mapping and analysis. All soils on the lower slopes, unlike those at upper elevations, contained accumulations of salts and gypsum, but the depth of salt accumulation and therefore the kind of soil appeared to be related only partly to current groundwater flow directions and the depth of the water table. The sodium content of the discharging groundwater and past flow conditions also appeared to be important. Lateral flow above the water table is suggested as being of possible importance in desalinization of surface horizons.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1975.tb01952.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY