摘要:

SummaryThe activity ratio aK/√(aCa±Mg) had the same value for all solutions in equilibrium with a chosen soil, regardless of their concentration (up to 0.06 M), or of the proportion of Ca to Mg.The activity ratio may be expected to provide a satisfactory measure of the ruling chemical potential of labile K in a soil, provided it is not used to compare soils of widely different Ca (and Mg) status, or a few soils of which the activity ratio is not independent of the concentration of the soil soluti

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00239.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryThe Q/I relations of labile soil K relate its availability or intensity (I) to the amount (Q) present. The activity ratio aK/√(aCa±Mg) has already been proposed as a measure of the intensity factor (part I). The ability of a soil to maintain the activity ratio against depletion by plant roots is governed partly by the character of the pool of labile K and also by the rate of release of fixed K, and by the diffusion and transport of K ions in the soil solution. We may isolate the Potential Buffering Capacity of the pool of labile K by determining theQ/Irelation over short periods. Suchimmediate Q/I relationshave been determined for a number of soils. They are all linear over the range of activity ratios commonly encountered in agricultural soils and approximate to familiar ion‐exchange equations. At low values of the activity ratio theQ/Irelations are all curved and asymptotic to the Q‐axis.The effects of drying, pH, the addition of lime or K fertilizers, and changes in temperature on the form of theQ/Irelations are reported.Oven‐drying a soil, particularly if repeated, appears to cause proportionately more K than Ca to be fixed in the fine clay

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00240.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryThe method of determining the activity ratio(AR) described by Beckett in Part II of this series was applied to a range of moderately to intensely acid Nigerian soils. With the highly acid soils it was necessary to add aluminium ions to the solution to obtain equilibrium. A method for obtaining the true equilibrium solution composition for K, (Ca±Mg), and A1 is described, and a series of typical results given. It was necessary to add benzene to prevent biological activity during sedimentation at 33° C. Altering the total concentration of the solution did not affect the activity ratio. A minority of soils showed evidence of transfer of potassium to non‐exchangeable forms during equilibrium. The slopes of the (exchangeable K)‐AR curves in a single soil were dependent on the amounts of soil Ca±Mg present. In comparisons between several soils, exchange capacity also had an effect. The Gapon equation was approximately correct for these soils over limited

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00241.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryThe composition of the topsoil in Nigerian oil palm plantations is expected to be closely related to the potassium status of the palms. K‐(Ca±Mg) activity ratios obtained from the equilibrium solution data presented in Part III of this series were not related to potassium yield response in field experiments on highly acid soils. This conclusion is supported by the failure of liming to affect potassium response, though the equilibrium activity ratios of acid soils are strongly affected by it.A relationship was found between yield response and the K‐(Ca±Mg) activity ratios of the soils determined in presence of sufficient lime water to remove soluble aluminium.A better relationship was obtained between yield response and a ‘unified activity (K±) ratio’, called ARu, the activities being those found in the true equilibrium solutions. ARuwas found to be far less dependent on exchangeable Ca±Mg than the K‐(Ca±Mg)

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00242.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryThe causes and mechanisms of phytotoxicity that can bring about poor or adverse crop responses to applications of solid urea to soil are reviewed. Compounds which may cause phytotoxicity are urea, transformation products of urea formed during manufacture (biuret), and transformation products produced in the soil or in plants (cyanate, carbamate, ammonia, and nitrite). Of these, ammonia and nitrite are considered to be the most likely causes of phytotoxicity when urea of low biuret content is used.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00243.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryPlant damage and reduced yields were associated with delayed ammonification or nitrification of added urea‐nitrogen. In a neutral sandy loam, the adverse effects of urea application were associated with the accumulation of toxic levels of first ammonia and later nitrite. Addition of hydrogen‐ion as phosphoric or sulphuric acid alleviated the damage thereby supporting the conclusion that ammonia and nitrite accumulation were the causes of phytotoxicity. In an acid sand, toxicity was associated first with the presence of large quantities of urea remaining in the soil though the evidence was insufficient to show in what way the urea was toxic. There was then a second phase of toxicity associated with the presence of considerable quantities of ammonium‐nitrogen under conditions where toxic levels of ammonia were likely to have occurred. The later phase (nitrite toxicity) did not occur. Phytotoxicity arising from urea addition to the soil could be due apparently to the persistence of urea as such in the soil and also to the accumulation of significant quantities of free ammonia and nitrite. The occurrence of one or more of these phases of urea toxicity depended on differences in soil condi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryA broad group of pedological features has been recognized by their occurrence as three‐dimensional entities embedded in the matrix of soil materials. They have been namedglaebulesand are divided into sub‐groups on their internal fabric, mineralogy, distinctness as a unit, and shape. These features include nodules, concretions, and septaria which have all been recognized by the petrologist, and pedodes, papules, and glaebular haloes which are newly recognized features. An attempt is made to interpret the origin of these features in terms of processes of formation and inheritance versus formation in situ. This is based on interpretation of the characteristics used for their classificat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryAn exchange equation based on positively adsorbed cations is derived using the double layer model. Some calculations using this equation are compared with calculations using the original Eriksson equation as written by Bolt.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryExamination of data on North Wales soils shows that a good correlation exists between loss‐on‐ignition and organic C values, determined by Tinsley's method. Ignition for half an hour at 850° C, and for 16 hours at 375 ±5° C have both been employed. The latter has advantages over the former procedure. Regression lines and prediction limits for organic C from loss‐on‐ignition are given from the data obtained. Although these regressions are not necessarily expected to be generally applicable, examination of some published data suggests that closely similar expressions may be. The method, because of its simplicity, can be usefully applied in a wide range of survey, analytical and ecological studies, in spite of the known source

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SummaryExchangeable manganese extracted from soil with calcium nitrate solutions shows some increase as the period of extraction is prolonged. For a given time of extraction the exhangeable manganese of soil behaves as a typical divalent cation obeying simple exchange theory, contrary to a previous report in the literature. Soil particles discriminate between calcium and manganese ions, calcium ions being held more firmly.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1964.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY