摘要:

SUMMARYLabelled urea was applied to monolith lysimeters in the 1st year of a 2‐year experiment at Onne in south‐east Nigeria. On eight lysimeters maize and rice were grown in each of the 2 years. Four lysimeters were similarly cropped in the 2nd year after being uncropped in the 1st year. Measurements were made over the 2‐year period of labelled and unlabelled mineral nitrogen in the drainage water, and labelled and unlabelled nitrogen in the crops. At the end of the experiment, weeds and the soil were also analysed for labelled and unlabelled nitrogen.The total recovery of15N in crop, soil and leachate varied between 70 and 93%. It was lowest when applied to the second season rice crop, which recovered only 15%, and highest when it was leached in the 1st year or was taken up by the maize crop. The highest crop uptake was 31%. The results indicate that, depending on the treatment, between 10 and 30% of the15N was immobilized in the soil, lysimeters cropped in the 1st year lost between 22 and 29% of the15N in drainage water, and between 7 and 30% was lost by denitrification. The accuracy of these figures is disc

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01233.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe effect of lime (CaCO3) and phosphate additions on surface charge characteristics and their effect on the leaching of sulphate were examined for two soils (Patua loam and Tokomaru silt loam) which differed in their adsorption capacities for sulphate.Incubation of soils with either CaCO3(0–600 mmol kg−1) or phosphate (0‐208 mmol kg−1) resulted in a two‐ to five‐fold increase in the net negative charge and a similar decrease in the adsorption of sulphate. The effect of either lime or phosphate addition on both the surface charge and sulphate adsorption was more pronounced for the allophanic Patua soil than for the Tokomaru soil containing mainly vermiculite.In a column experiment, liming induced the leaching of sulphur either by the desorp‐tion of adsorbed sulphate or by the mineralization of organic sulphur. During a miscible displacement study, addition of either CaCO3or phosphate resulted in an early breakthrough of sulphate in the leachate. In a pulse experiment, in which soils were incubated with sulphate (3.12 mmol kg−1) for 1 week and subsequently leached with water, more added sulphate was lost in the leachate of the soils previously incubated with either Ca

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01234.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYCHAOS (Complexation by Humic Acids in Organic Soils) is a quantitative chemical model of organic soils that incorporates complexation by the functional groups of humic substances and non‐specific ion‐exchange reactions. The two types of interaction are linked by the net humic charge, Z, which depends on the extents of proton and metal complexation, and which in turn determines ionic concentrations in the diffuse part of the electrical double layer, by a Donnan equilibrium. CHAOS was found to account satisfactorily for the results of acid‐base titration experiments (pH range 3–5) with soil samples, giving reasonable simultaneous predictions of solution pH and concentration of A13+. Predictive calculations with CHAOS suggest that organic soils acidified by acid rain would respond on a time‐scale of years‐to‐decades to reductions in rain acidity. An associated effect might be an increase in the concentration of dissolved organic matter in the

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01235.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYRoot exudates were collected from maize plants (Zea mays L.), grown under sterile and hydroponic conditions. Exudates of low molecular weight were isolated by filtration and dialysis (MW 1000) of the nutrient solution and analysed. Metal binding properties of the exudates were investigated at 25°C in 0.1mNaCIO4ionic medium, using a potentiometric method. The total acidity of the exudates and the successive stability constants of complexes formed with Cu2+, Pb2+and Zn2+were determined.Sugars and organic acids were the major components of the exudates. Measured total acidity was resolved into strong (5.85meq g−1C), weak (2.10meq g−1C) and very weak (2.20 meq g−1C) acidities. Mono‐complexes were formed with Cu, Pb and Zn and bis‐complexes with Cu. At pH 5, stability constants followed the orde

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01236.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYCarbon, Al and Fe (Cpyr, Alpyrand Fepyr) were extracted with 0.1mNa4P2O7from 26 A horizon samples of tropical Thai and temperate Korean soils (Ultisols, Alfisols, Oxisols and Inceptisols). The soils, except for one Thai Inceptisol, had similar total C (0.35–3.29%) and Cpyr/total C ratios (0.20–0.41). There were approximately linear relationships between total C or Cpyrand clay content; two groups of soils gave different linear relationships. A curvilinear relationship between Cpyrand (Al + Fe)pyr(milli‐atom kg−1) that can be approximated by an equation: Cpyr= 53 (Alpyr+ Fepyr)1/2– 24 was also found for most Thai and Korean soils. The above relationships indicated that total C and Cpyrwould be close to zero at zero clay or zero (Al + Fe)pyr. It was inferred that clay‐humus interaction has a primary importance in the determination of humus content in red and yellow soils in tropical and temperate regions and that the main role of clay is to supply Al and Fe that complex and stabilize humus against microbial

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01237.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYSurface soil samples from seven profiles from the central plains of Sudan were investigated using XRD, chemical analysis and Mössbauer spectroscopy measured at 15K. Dioctahedral montmorillonite was the main constituent with different proportions of kaolinite and chlorite. Goethite was found as fine iron oxyhydroxide in all the samples, with haematite detected in two pedons. Crystallinity of the clays was observed to correlate negatively with the amount of free iron oxide in the soil. The influence of the climatic factors on the soil and its formation is discussed

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01238.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYPrevious investigations had shown that about 80 years of Norway spruce monoculture on an ochreous brown earth of the Belgian Ardennes were sufficient to accentuate the weak podzolization process already present in the climax beechwood soil and to increase the weathering of several minerals, e.g. 2:2 clay minerals. In order to evaluate more accurately mineral weathering and spruce‐induced losses of nutrient elements, an isoquartz assessment method has been applied to a pair of soil profiles, one developed under beech, the other under spruce.Results show a clear decrease of several weatherable minerals in the soil of the spruce stand which was more marked than in the beechwood, especially for chloritic minerals: losses reach about 30% of the initial chlorite content in the cambic horizon and regularly increase up to 70% in the humic layer. There were severe spruce‐induced losses of Mg and Na: 27% of the initial Mg reserve was removed from the whole soil and the losses reached 60% in the upper 20 cm.It is concluded that 86 years of Norway spruce monoculture have appreciably increased weathering processes and removal of eleme

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01239.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYSplash droplet characteristics were studied using cine‐photography and a simple droplet collection method. Two sizes of falling drop, two heights of fall and a number of target materials including soil, sand, water and rotating sandpaper were used. For a 6 mm drop falling at near terminal velocity about 5000 splash droplets were collected ranging in size from 10 um to more than 3 mm in diameter. The amount of soil material carried by splash droplets was much less in the presence of surface water and increased with the size of water stable aggregates. The energy and momentum balance showed a higher proportion of impact energy and momentum in the resulting splash droplets as the impact energy increased. This suggests that kinetic energy is not a reliable indicator of the erosivity of rain drop

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01240.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe compressive‐tensile stress ratio at failure under unidirectional loading of air‐dry samples of 10 soils was compared with their clay and CaCO3contents, and their surface areas. Deviations from the commonly assumed Griffith theory were found for two soils. No special relationships were found between soil constituents and associated compressive tensile stress ratio, even though this ratio tends to decrease slightly with increasing clay percent

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01241.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYWhen stones prevent the measurement of cone resistance, and missing values below the stones are ignored, then averages can be seriously underestimated. Methods are considered for correcting this bias and an algorithm is proposed in which missing observations are replaced by their expected values. A numerical example gives results in close agreement with those obtained using the optimal, but computationally expensive, method of maximum likelihood estimation. It is recommended that data from incomplete penetrations should not be discarded but should be used, preferably with the proposed algorithm, to reduce the bias in estimates of mean values.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01242.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY