摘要:

Abstract.The erosion susceptibility of the Erosion Research Farm at Kabete Campus was mapped using a qualitative parametric method. A grid soil survey of the 4 ha farm was combined with a map of slope gradients, slope segments being delineated by breaks in slope. Rainfall erosivity and soil erodibility were also measured. Areas with the greatest erosion susceptibility according to this method were those occupying convex slope positions and slopes of more than 30%. Field observations and soil loss measurements generally supported the erosion susceptibility rating map produced by this method. The soil and erosion susceptibility maps were useful for planning erosion control measures and for selecting suitable sites for runoff plot experiments.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00486.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.The decline in topsoil (0–0.1 m) pH (CaCl2) over 11 years (1979–90) was measured in a rotation, tillage, stubble and nitrogen fertilizer experiment on a Chromic Luvisol at Wagga Wagga in S.E. Australia. The rotations consisted of annual wheat cropping (WW) with and without nitrogen fertilizer (100 kg N/ha/year), alternating lupin‐wheat (LW) and subterranean clover‐wheat (CW). The initial mean pH at the site was 4.9 and the experiment was preceded by subterranean clover‐based pasture for most of the previous 19 years. An initial rapid decline in soil pH under all treatments over the first 8–9 years was followed by a 2–3 year period when no further decline was detected. The annual rate of pH decline over the first 8–9 years varied from 0.06 for WW to 0.09 units for WW with added N fertilizer. Apparent steady‐state for WW after 11 years was approximately 0.5 pH units higher than for WW with added N fertilizer. There was no difference between CW and LW in the rate of decline or in the apparent steady‐state reached. Six years’ stubble burning in a LW rotation promoted a slightly higher pH than where stubble was retained. However, there was no significant effect of tillage in either LW or CW rotations. By 1990 the addition of N fertilizer to WW had increased the concentration of exchangeable aluminium by 100% and of manganese by 24%. The inclusion of a legume in the rotation increased the concentration of aluminium but did not affect manganese. However, burning stubble in the LW rotation slightly decreased man

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00487.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.England and Wales have 155 314 1 × 1 km squares, of which 140049 have more than 50% soil cover. The total soil organic carbon content, based on the dominant soil series and dominant land cover type, is estimated to be 2773 × 106t C. Scotland has 84929 1 × 1 km squares, of which 82 420 have a nominated dominant soil series. The total soil organic carbon content is estimated to be 19011 × 106t C, 6.85 times the total organic carbon content of the soil of England and Wales. The total organic carbon content of the soil of Great Britain is estimated to be 21 784 × 106t C, of which 87% is in Scottish soils and 75% is in Scottish peats.A map of the mean soil organic carbon content of 10 × 10 km squares of the National Grid using classes of equal range illustrates the narrow range of organic carbon contents of the soils of England and Wales and the dominance of organic carbon in Scottish soils. A map using the same data, but with classes of unequal ranges increasing in size with increasing carbon content, is better for showing detailed differences within England and

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00488.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.The Agricultural Catchments Research Unit model (ACRU) includes a decision support system (DSS) for estimating the water content of soil at field capacity (θfc) and wilting point (θwp) when these characteristics are not directly measurable. Three methods of estimation are proposed: (a) based on silt and clay content and bulk density, (b) based on clay content only, and (c) based on soil series. These three pedotransfer functions are compared with respect to both the estimation of θfcand θwpand the propagation of errors when the actual evapotranspiration of a wheat crop (E) is predicted over the growing season by the ACRU model.The standard error of estimation was between 0.066 and 0.082 m3/m3for θfc, between 0.056 and 0.069 m3/m3for θwpand between 29.9 and 34.8 mm of water for E. The method based on silt and clay contents and bulk density predicted θfcand θwpfor non‐swelling soils most precisely. The method based on soil series was better than other methods for swelling soils. It also performed better for estimating available water capacity and consequently for predicting E from a conceptual soil water model. The propagated error of estimating θfcand θwpusing the DSS reached 15–18% of the simulated E. The error in the prediction of E can reach 26–30% when spatial variation in soil properties is

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00489.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Land cover data from the June agricultural census of England and Wales have historically been published annually at the parish level. This level of spatial resolution masks heterogeneity of land use within parishes, limiting the value of the data for detailed spatial analyses. However, variation in land characteristics across parishes can be used to model variation in land cover, thereby allowing the spatial basis of the census data to be transformed. This procedure, referred to as areal interpolation, is illustrated using two land classification systems based on soils for a study area in northern England. The results indicate that the spatially transformed data offer a better description of the distribution of land covers than that provided by the raw census data. They also demonstrate the extra value that can be obtained by combining extant data sources within a GIS framework. Potential roles for areal interpolation in environmental modelling and policy formulation are discussed briefly.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00490.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.Finely ground calcium carbonate was applied at six rates (0–7.0 t/ha) to samples from four depths of an acid tropical soil (Oxisol). The mixtures were kept moist and maintained at 18 °C for a period of 30 days. There was a significant increase (>28%) in soil pH at all the sampling depths. Extractable P also increased significantly (>90%). Significant positive correlations between pH, extractable P and liming rate were obtained (r>0.9,P= 0.01). The effect of time was significant only on the 10th day after liming, when soil pH had stabilized. Exchangeable Al was completely eliminated on the 5th day after liming, when most of the soil samples had pH values>5.0. The results clearly indicate that liming, as a management practice, could be used to alleviate or prevent acidification of Oxisols like the soil studi

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00491.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.The disposal of water treatment sludge produced when turbid water is treated with flocculants (alum and polyDADMAC) and filtered for clarification is becoming increasingly expensive in South Australia. The physical and chemical properties of the sludge suggest that it might be used as a plant growth medium, and a glasshouse experiment compared the growth and elemental composition of broad beans in both alum and polyDADMAC sludge applied at different rates.Dry matter production differed significantly between treatments. Poly + Fertilizer (F) and Poly 4%+ F produced the most dry matter. The Alum + F treatment produced significantly less dry matter than the Poly + F treatment but it was not significantly different from the control. The difference in plant growth between the pure poly and pure alum treatments resulted from increased availability of the fertilizer phosphorus in the poly sludge and the supply of some potassium and nitrogen by the poly sludge. Fertilizer was required for optimum plant growth. Greater rates of fertilizer may be required if alum sludge is to be used as a growth medium, than if poly sludge is used.There was no evidence that aluminium toxicity would be a problem if water treatment sludges are used as growth media. The physical properties of the sludges (i.e. water holding capacity, drainage characteristics and structural stability) are probably more important than their inherent nutrient levels, although poly sludge does supply some nitrogen and does not fix phosphorus to the same extent as alum sludge.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00492.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract.The efficiency with which fertilizer nitrogen (N) is used in agricultural systems might be improved if the amounts applied at each top dressing were adjusted to avoid the accumulation of mineral‐N in the soil profile to levels in excess of the growth requirements of the crop. Such tactical application of fertilizer would be feasible if soil mineral‐N could be determined rapidly in the field with sufficient accuracy. This paper describes a rapid field test for both the ammonium and nitrate components of soil mineral‐N based on reading paper test strips with a reflectometer, recalibrated for use with KC1 solution. The new test is volumetric and also accounts for the effects of fluctuations in soil water content by means of a standard dilution procedure to provide an absolute measure of soil mineral‐N in about one hour. Measurements of ammonium and nitrate in a clay loam soil sampled from grazed pasture were compared with those made by conventional laboratory based methods; they generally differed by less than 5%. The proportion of mineral‐N as ammonium averaged about 50% overall and typically exceeded 70% in spring. Ammonium and nitrate were not well correlated. The use of a filter‐press to expel soil solution increased the sensitivity of the test five‐fold to enable application in studies of soil N transformations in unfertilized and semi‐natur

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00493.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Book Reviewed in this article:Estimating fertilizer requirements: a quantitative approach By J. D. Colwell.Soil Science: methods and application By David I. Rowell.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00494.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1995.tb00485.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY