摘要:

Abstract.Leaching losses of nitrate‐nitrogen were measured from a set of eight hydrologically isolated plots on a clay loam soil over the period from September 1987 to February 1990. Variable drainflow recovery from the plots hampered accurate estimation of nitrate loading, but results suggest that, when inorganic nitrogen fertilizer is applied up to the recommended amount, there is little influence of the amount applied on the amount leached. We did, however, observe the following effects on nitrate leaching: leguminous green manure incorporated in autumn increased leaching of nitrate‐nitrogen by 10–15 kg per hectare during the winter; autumn cultivation caused some increase in leaching compared with no cultivation in one year; some systematic variations in nitrate leaching occurred between years and between plots, but were unrelated to treatments.From the results we conclude that green manuring does not provide sufficient nitrogen for organically grown crops on this soil but contributes significantly to nitrate leaching, and that growing spring cereals, with the land remaining in stubble as long as possible in autumn, may be the best strategy to minimize nitrate lea

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.During the four consecutive winters between 1984 and 1989 a computer simulation model was used to estimate the amounts of nitrogen in a cereal crop and available from soil to the crop after winter. The model does this by taking account of daily weather and by making simple assumptions about the starting conditions each autumn after the harvest of the previous crop. Some of the information which was given to farmers on viewdata systems is displayed, together with maps showing the average amounts of nitrogen in soil and crop in spring over 10 years in eastern England. This 10‐year average is used as a baseline against which to judge the simulations in each of the four winters of our viewdata servic

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A Land Evaluation System for rainfed agriculture has been developed in Zambia. It is intended for use in reconnaissance and semi‐detailed land evaluation studies, and works with 74 subqualities, 40 crops and four input levels. The subqualities are rated and converted into constraint classes per input level. The most limiting constraints determine the final suitability class. Expected yields per suitability class and input level are then estimated. The system was calibrated by a field study at four locations. Comparisons were made between expected and actual yields and expected and actual constraints. The range of actual yields was wider than that expected, probably because of variation in management between farmers. The average actual and expected yields were strongly correlated, but chi‐squared tests showed that they were significantly different. The system generally works well in assessing land suitability for crops commonly grown in Zam

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Experiments were started in 1967 to investigate the effects of soil mixing on fen peat soil. Peaty topsoil was mixed with mineral subsoil to a maximum depth of 80 cm at two sites, one with a clay subsoil, the other sand. Mixing was done on a commercial scale with a range of implements. After initial increases, yields of arable crops on both mixed soils were subsequently similar to those on unmixed soil. Residual herbicide activity was enhanced on mixed soils, and evidence of peat conservation was obtained at one site. The practice has not been taken up commercially because of the high capital cost of mixing and lack of serious problems which had been predicted following peat wastage.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In 1989–90 over 80% of the erosion on agricultural land in the South Downs was on ploughed or cultivated surfaces prepared for spring planting of cereals. This was in contrast to the pattern in previous years when most erosion was in winter cereal fields. An unusual late winter rainfall peak was the primary cause. Periods of erosion risk associated with other land uses on the South Downs are also discusse

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Various factors of soil erosion (erodibility of the soil, slope of the land and nature of the plant cover) were studied in a representative area of submontane Punjab. In the north‐eastern part of the area, slope steepness, slope length, convexo‐concave and concave slope patterns and sparse vegetation were the dominant factors governing erosion hazard. In the central and lower south‐western part of the area, high soil credibility and sparse vegetation were the most important factors.Rill erosion was positively correlated (r= 0.87) with slope steepness. The erodibility of the soil was strongly correlated (r= 0.98) with amounts of silt + very fine sand.In the area with steeper slopes, the lower segments of transects were prone to more erosion because of high credibility. Slope shapes such as convexo‐concave and concave could result in sloughing and greater erosion hazard if not properly protected. Slopes facing southwest were more prone to erosion than others because of more solar energy, greater aridity, less vegetation and concav

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Linear, exponential and power function regressions were compared for rainfall, runoff and soil loss data. The power function performed better (R2= 0.77) than exponential or linear functions for estimating runoff from daily rainfall. However, this relationship was improved (R2= 0.96) by inclusion of a random component to the deterministic part of the function. A linear relationship between runoff and soil loss data performed better (R2= 0.77) than exponential or power functions. These relationships help in designing soil and water conservation works for supplemental irrigation in the area.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.In arid regions of India, cultivation of marginal areas and overgrazing of pastures have resulted in degradation of land. Accelerated wind erosion on sandy surfaces and water erosion on the shallow soils of piedmont areas are both common. Landsat Thematic Mapper sub‐scenes have been used to map the type, extent and degree of degradation. In an area of over 5000 km2, 42% was affected by wind erosion and 50% by accelerated water erosion. A quarter of the whole area needs urgent attention for soil conservatio

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The essential factors dependent on soil structure that influence plant growth are soil/root contact, adequate air and water, and low mechanical impedance. Bulk density, shear strength and texture arc interrelated closely and permit quantification of these factors. A general relationship between clay content and vane shear strength of soil at field capacity and non‐limiting bulk density provides a rapid means of quantitatively estimating structure. We propose a procedure utilizing vane shear strength and a tactile assessment of clay content as criteria for judging soil structure in the fiel

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Relationships between soil colour patterns and depth and duration of water tables were studied using piezometers in three soil hydrosequences. A colour index was developed to quantify matrix colour, size and colour of mottles, and continuity and colour of clay films. It correlated well with duration of saturation when above 5°C (r= 0.88) and with duration of total saturation (r= 0.87). The colour index is useful to evaluate soils for various land uses

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY