摘要:

SummaryEarlier studies have shown that the K‐(Ca+Mg) exchange isotherms of field soils are not greatly changed by cropping, by additions of K‐fertilizer, nor by moderate release of K from fixed forms. The present work shows that very prolonged K‐enrichment or depletion in the Broadbalk trials has led to substantial differences between the exchange isotherms of soils from adjacent plots in proportion to the severity of their K‐depletion.It is suggested that the changes result from the removal of inter‐lamellar K and the consequent increases in the inter‐lamellar spacings of parts of the clay crystals, which have increased the extent of the surface areas accessible to K‐(Ca+Mg) exchange. It is possible that increases sufficient to cause substantial changes in the exchange isotherms may not be apparent in X‐ray diffraction diagrams. Treatment of the K‐depleted clays with m CaCl2appears to contract the newly expanded parts of the clay crystals, so that exchange on the occluded surfaces is once again too slow to be observed by th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01549.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryPhysical analyses of 15 Orthic Podzols of south‐eastern Quebec, Canada, showed that the extent of the breakdown of the gravel, sand, and silt and the accumulation of clay was dependent on the porosity of the parent material and the type of rocks in the gravel. There was no clay accumulation in the B horizon when the results were expressed on a percentage weight per unit volume basis. The sand was fractionated into five grades. The specific gravity of the gravel was smaller than that of any sand fraction and that of the sand increased towards the finer fractions. The specific gravity of the gravel also increased down the profile; that of the sand did not. These changes were also related to the type of parent material.A value for each horizon, calculated as follows:was used as an index of weathering to show the degree of weathering intensit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01550.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummarySoil texture was mapped in the immature alluvial soils of the Lower Indus plain. A disadvantage of soil texture as a mapping criterion in such soils is the great complexity of their textural patterns. The geomorphological background of the Lower Indus plains is examined, and a classification of texture and textural profiles is defined. The mapping unit proposed, the‘textural association', comprises a certain range of textural profiles within a given landform, related to each other by the modes of deposition which established that landform. It seems likely that the textural association could, in more detailed surveys, form the basis of a soil series classificatio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01551.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryThe decomposition of grasses and rye labelled with14C was studied using ground material and also fragments cut from intact leaves or roots either placed on the soil surface or buried in the soil incubated under various conditions. Autoradiography was used to observe the changes in the decaying plant tissue with a minimum of disturbance. Autoradiograms prepared before incubation and subsequently at intervals reveal an over‐all fall in density of the images, a complete disappearance of14C in small discrete sites, as well as a dispersion of14C over distances of several cm from the plant residues.A photoelectric technique was devised by which changes in density could be expressed quantitatively. The log density of autoradiographic images of pellets of ground grasses shows a predominantly, though not completely, linear regression on time of incubation. The method has shown that the process of decomposition is very slow, that in the first stages of decomposition ryegrass decays faster than cocksfoot, and that ground material tends to behave in a different manner to fragments cut from intact tissues. Changes in the area of autoradiographic images with time of incubation could be used as an additional but less sensitive measure of the rate of decomposition.The participation of micro‐organisms (especially fungi) in the breakdown of the plant tissues has been demonstrated by the presence of labelled organisms in the vicinity of plant residues. Labelled fungi are more numerous in the first 3 months of incubation, during which a marked fall in image density of the plant residues occurs. A further decrease in image density is frequently associated with the appearance of fungal resting structures with a greater concentration of14C than the surrounding plant fragments. Because of their longevity these structures contribute to the fixing of14C in a different fraction of the biomass. Faecal pellets of soil mesofauna also concentrate14C and resist decomposition for very long periods of t

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01552.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryIt is pointed out with the help of the Independent Domain Theory, that a fraction of the pore‐water constituting a volume ΔVis contained in pores not common to both the wetting and drying states and that this volume in a wetting state is contained in pores whose draining radii are greater than those of the pores containing the water volume ΔVin the drying state.On the above basis it is suggested that hysteresis may affect the hydraulic conductivity: firstly, through differences of the radii of the pores containing the water volume ΔV, which tend to endow a wetting state with a conductivity greater than that of an equally wet but drying state; secondly, through differences of the coordinates of the above‐mentioned pores, which may influence the paths of flow and consequently the hydraulic conductivity, and will have either a similar or opposite effect. It is concluded, therefore, that the conductivity in the wetting state can be greater, equal, or even less than that in the drying state, depending on the particular porou

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01553.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryThe rate of loss of total P and accumulation of organic P were investigated in a chronosequence of weakly weathered soils developed on wind‐blown sand. The net loss of total P during 10 000 years of soil development was 1910 kg/ha m profile. This calculation assumes a constancy in the total P content of the parent material. An approximately straight‐line plot was obtained for the loss of total P between 500 and 10 000 years. The organic P content of the beach sands was very low but increased rapidly in the early stages of soil development. With increasing time, the rate of accumulation of organic P decreased. The net accumulation of organic P during 10 000 years was 1050 kg/ha m profile. A slow rate of formation of organic P, coupled with a rapid mineralization, has probably limited organic P build‐up. It is suggested that loss of phosphorus by leaching is a consequence of the low phosphate retention capacity of these weakly weathered

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01554.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryMost of the Cu previously added to humic acid derived from a sedge fen peat was easily removed by washing with acid, but the strength of binding increased as the Cu content decreased. The capacity to retain firmly bound Cu was reduced to about half by treating the humic acid to block either carboxyl or hydroxyl groups alone or to block both groups together. The retaining sites blocked therefore probably involve both carboxyl and hydroxyl groups acting together, but alternatively could be groups such as hydroxy‐quinone, affected by both types of treatment. Retention of Cu by peat differs from retention by the extracted humic aci

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01555.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryConventional K: Al exchange isotherms for montmorillonite showed that Al3+was strongly preferred to K+in o‐oin solutions. The exchange coefficient,K', calculated using the isotopically exchangeable K, was greater than unity and did not vary with the Al‐saturation or with the initial pH of the AlCl3solutions.Isotherms for vermiculite, illite, and soils in o·oin solutions also showed Al3+‐preference but unlike those for montmorillonite were not asymptotic toqAl/qo= 1,qAlbeing the amount of adsorbed Al andqothe total adsorbed (Al + K), indicating that some of theisotopicallyexchangeable K could not easily be exchanged by Al3+ions; thisdifficultly exchangeableK (DEK) was estimated for each exchanger.K'values for vermiculite, illite, and soils were less than unity and did not vary with Al‐saturation or initial pH if the isotopically exchangeable K was corrected for DEK. This showed that K+was adsorbed more strongly than Al3+. Strengths of K+adsorption referred to Al3+as the counter‐cation were in order: soils>vermiculite, illite>montm

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01556.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryDistinctive channel patterns in the floors of alluvial clay depressions in Iraq and Sudan as well as in other parts of the arid zone have been described as gilgai in the past though their morphology differs from examples of gilgai as originally described in Australia. The soils on which the channels develop vary considerably and do not always contain large proportions of expanding lattice clay. The formation of the micro‐relief may not necessarily involve heaving of the subsoil as in the Australian gilgai. It is formed rather by a process of uneven settling and compaction, the patterns of channelling being controlled by pre‐existing surface irregularities. If the formation of the micro‐relief does not involve heaving, it is probable that the channels will not reform after reclamation. The term‘tabra channels’ is suggested for th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01557.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SummaryMethods used for measuring labile P and assessing the phosphate‐fertility status of soils by isotopic dilution as well as assumptions involved in applying the isotope dilution technique were critically evaluated.In the presence of high phosphate‐fixing compounds, e.g. reactive iron oxide, labile P may be erroneously overestimated; especially when carrier‐free32P is used. At the end of the isotopic‐exchange reaction period, high phosphate‐fixing soils may have a higher specific activity in the solid phase than in the solution phase. Methods involving the use of a 0·2 ppm P carrier solution or the addition of an unlabelled carrier to a labelled soil may give satisfactory labile P measurements in low and in medium phosphate‐fixing soil. All the methods tried (carrier‐free, carrier, and inverse dilution), however, failed to give satisfactory results for the high phosphat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1969.tb01558.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY