摘要:

Abstract.Information on land resources and the capacity of land to support agricultural production is a prerequisite for the formation of sound agricultural policies. This paper summarizes Canadian experiences in developing national and regional land evaluation systems. Potential users expected the system to estimate the degree to which changes in biophysical and socio‐economic conditions would alter options for land use and production, and to provide a context for more detailed analysis.A broad‐scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub‐provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad‐scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system deve

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00884.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.This paper describes the application of prototype Canadian land evaluation systems to selected issues. Two categories of applications are recognized. Routine evaluations employ standardized data sets and provide a backdrop for framing broader land‐related concerns (e.g. assessments of land supply and suitability). Iterative analyses investigate implications of modified conditions (e.g. soil erosion, global climatic warming, altered food demands) on land use and production options, and require additional data and expertise. The paper demonstrates the capacity of land evaluation systems to address a wide range of issues, and illustrates the range of skills required to maintain and apply these system

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00885.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Results of the Representative Soil Sampling Scheme between 1978 and 1988 show that soil acidity remains widespread, particularly in Wales, and suggest that the proportions of grassland with low pH increased during this period in the traditional grassland areas of England and Wales.Average soil nutrient levels changed little over the decade. However, at least one in five grassland fields are likely to suffer yield restrictions because of shortage of soil P or K (index 0). One in four arable fields were found to be at index 1 for K, indicating that many crops are being grown at potassium levels which can be described as borderline. On the other hand, 22% of arable crops were grown at phosphate index levels in excess of 3, so phosphate savings could be made on many crops. Texture and calcium carbonate levels and their relationships with nutrient levels are also examined.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00886.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The accuracy of assays based on galactosidase and the enzyme‐linked immunosorbent assay specific toThanatephorus cucumeriswere compared with techniques based on soil dilution plating and baiting in sterilized field soil. Although soil dilution plating is reasonably quantitative, it requires substantial time, material and labour. Plant baits gave inconsistent results in the estimation ofT. cucumerispopulations in the soil. Enzyme‐linked immunosorbent assay (ELISA) using monoclonal antibodies is suitable for detecting the presence of a range of anastomosis groups (AGs) of 71cucumerisin soil samples, but more quantitative applications seem to be limited to a very narrow range of concentrations of the fungus (0–10 μg/g). Monoclonal antibody ELISA could be used if the soil samples are routinely further diluted, provided the range of concentrations is uniformly low. An assay of β‐galactosidase permits estimation of a more adequate range of concentrations (0–500 μg/g) and may be used in defined experiments using uninoculated

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00887.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Uniform application rates of fertilizers and herbicides may result in over‐treating some soils and under‐treating others; costs may be unnecessarily large and soil, ground water and surface waters may be contaminated. An alternative is site specific treatment, tailored to individual soil types present in agricultural fields of any size. To study the pollution hazards of the herbicide alachlor, leaching and adsorption experiments used disturbed samples and undisturbed soil columns. Adjoining Ves, Normania and Webster soil series (Udic Haplustoll; Aquic Haplustoll; Typic Haplaquoll) were sampled and analysed for various properties. Ring uniformly14C‐labelled alachlor was used to study adsorption and leaching characteristics in these soils. Results show different alachlor behaviour in topsoil and subsoil l

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00888.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The influence of trampling on the soils of the St James Walkway was studied during 1985 by comparing ‘on’‐ and off‐track sites. Trampling increased the average soil bulk density by 0.3 g/cm3at 0–5 cm depth and by 0.1 g/cm3at 10–15 cm depth. Trampling increased the average soil shear strength by 11 kPa at 0–5 cm depth and by 6 kPa at 5–10 cm depth. All mineral soils were compacted to some extent by trampling. The podzolized high country yellow‐brown earths (Dystrochrepts) were the most affected because their organic topsoil was truncated. Their exposed subsoil was however more resistant to further damage than their topsoil. Organic soils (Medihemists) were not compacted but their very low shear strength and high moisture content make them unsuitable for tracks. Untrampled soil bulk density and soil stone content were negatively correlated with the change in bulk density by trampling, and could be used to predict the risk of soil compac

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00889.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The influence of intensively fertilized short‐rotation forest plantations on nitrogen concentrations in groundwater was studied by piezometer readings and water sampling over a two‐year period in a sandy field growing willow (Salixspp.) and other species. The mineral‐N content of the unsaturated zone was measured in soil samples collected to 0.9 m depth. Although piezometer readings suggested that deep groundwater could be affected, the concentrations of nitrate‐N and ammonium‐N were usually less than 1 mg per litre. There was also little mineral‐N in the unsaturated zone, except for occasional peaks in the topsoil (0–30 cm) after application of fertilizer. We conclude that there is little risk of nitrogen contamination of groundwater in intensively cultured tree stands receiving up to 150 kg N/ha/yr as fertilizer. This is probably because willow can take up water and nitrogen from deep parts of the

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00890.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The tolerance of wheat plants to manganese is shown to depend on the magnesium concentration in shoot tissue, such that growth is a function of the ratio of the two ions Mg: Mn. This ratio in the plant (Rp) and in the soil solution (Rs) was related by the equation:ln Rp= 1.45+0.31 ln Rs.Values of Rpnot limiting to growth need to be determined for different crops, but we conclude that corresponding values of Rscan be predicted using solution culture trials. They can then be used to identify remedial treatments in soils where manganese toxicity occurs. In the Eutric Cambisol examined, small amounts of calcium carbonate decreased manganese concentrations in the soil solution such that amounts of magnesium which could easily be applied to a field gave appropriate values of Rsfor wheat.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00891.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Bypass flow and concurrent leaching of nitrogen were studied on a Vertisol in south‐western Kenya under rangeland and bare, manually tilled cropland. Showers of 30 mm/hr were simulated, causing bypass flow of 47–62% in rangeland topsoils and 19–49% in cropland topsoils. Volumetric water contents after experimentation increased from 28 to 35% and from 24 to 38%, respectively, for the two land‐use types.In rangeland samples up to 3.4 kg N/ha was found in the leachate of unfertilized soil. With a fertilizer application of 50 kg N/ha, up to 5.7 kg N/ha was lost from a pre‐wetted soil, and more than 20 kg N/ha from dry soil. In cropland topsoils up to 2.2 kg N/ha was lost from unfertilized soil, and only up to 2.9 kg N/ha from both dry and prewetted fertilized soil. Although Vertisols are often linked with excess water, the phenomenon of bypass flow can cause water stress to crops in their early growth stages. Nitrogen leaching losses were large from dry grassland, but prewetting helped to decrease them. On intensively cultivated cropland there was little nitrogen leaching; the tilled topsoil was able to retain most of the supplied

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00892.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Book review in this ArticleErosion, Transport and Deposition Processes Edited by D.E. Walling, A. Yair and S. Berkowicz.Statistical Methods in Soil and Land Resource Survey. By R. Webster and M.A. Oliver.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00893.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY