摘要:

Abstract.Soil profiles, first sampled between 1963 and 1973, were resampled in 1991 in an upland area with modertely high deposition of pollutants. One hundred horizons from 32 profiles, representing 10 different soil subgroups were analysed for pH and seven variables related to pH, using the same laboratory methods on both sampling occasions. To allow comparisons to be made with results obtained with these old methods, analysis of the 1991 samples was repeated for some determinands using the methods currently used in the analytical laboratory. Organic and A horizons show a consistent increase in acidity between samplings. Although brown soils and lithomorphic soils have increased in acidity throughout their depth, gleys and podzols have decreased in acidity at depth, probably because of poor water transmission downwards into these horizons. Correlations with other determinands suggest that the dominant process in the soils is leaching of basic cations and their replacement on exchange sites by protons and probably aluminium ions. A cause of the increase in soil acidity is likely to be the deposition of atmospherically transported pollutants.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00959.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Currently there is growing interest in the restoration of drained peatlands in Britain. In order to investigate some of the effects of changes in land management practices on the biogeochemistry of peatlands, a field experiment was designed to manipulate the hydrological conditions in a naturally drained acid gully mire in Mid‐Wales. We report preliminary results of the effects of experimentally rewetting the mire on the hydrochemistry of bromide in the peat‐water. Results show that rewetting had a dramatic effect on the concentrations of bromide, which increased substantially. Peak values approached 1 mg/dm3in some samples following rewetting, compared with typical values<0.05 mg/dm3under the drained conditions. Bromide was positively and significantly correlated with Dissolved Organic Carbon (DOC) in the peat‐water, which suggests that Br‐is derived from breakdown of organic matter in the reducing conditions following rewetting. The bromide mobilized by rewetting may be leached out of the system and/or re‐assimilated by the wetland vegetation. Further monitoring is needed to determine whether the observed hydrochemical response of bromide to rewetting of the mire has any longer‐t

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00960.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Monoculture winter barley was grown for 5 years with 80 or 160 kg/ha of fertilizer nitrogen (N) and established by either shallow cultivation (straw removed) or ploughing (straw incorporated) in a replicated 2 ± 2 split plot experiment. The lower N rate reduced average grain yield from 6.85 t/ha to 5.61 t/ha. The cultivation/straw disposal system had no effect on yield. Halving the N rate reduced the amount of N removed in the crop by an average of 40 kg/ha and reduced the amount of nitrogen leached by 11 kg/ha per year. Using a shallow cultivation system for crop establishment, following the removal of straw, initially reduced N leaching compared to ploughing in the straw, but in the later years of the experiment losses were similar. Over the five years the full N rate with ploughing system resulted in a small positive nitrogen balance of 66 kg/ha, but all other treatment combinations resulted in a negative balance

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00961.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.Nine different techniques were used to record the initial change in the physical and hydrological properties of a freshly tilled soil surface following successive cycles of wetting and drying. The study was made in the field on a sandy clay loam soil ploughed and harrowed and then exposed to three simulated rainfall events of 76 mm/h for 15 minutes. Although the degradation of the soil surface increased with each successive rainfall, the most significant changes were observed after the first rainfall. Qualitative observations of clod size distribution and crust development provide a good indication of the early stages of soil surface degradation. Complementary physical data were quickly obtained using a hand held shear vane. These techniques are simple and robust enough that they can be used in on‐farm research programmes, where resources, both human and technical are at a premium. Tension infiltrometry provided hydrological information that complemented the physical information provided by the above techniques, but is not as simpl

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00962.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.The understanding of nitrogen mineralization is central to providing good advice to ensure that nitrogen (N), from whatever source, is utilized by crops as efficiently as possible to minimize pollution. We have reviewed how mineralization is accounted for in current advice. It is clear that there is at least a qualitative understanding of the effects of soil and crop management on N mineralization and N supply, which has enabled the development of Codes of Good Agricultural Practice and fertilizer recommendations systems, based on sound scientific principles. However, to refine advice there is a need for a better quantitative understanding.Although soil organic matter (SOM) is a major source of N for crops, we are unable adequately to predict fertilizer requirement as affected by mineralization of SOM. Nitrogen returns from crop residues can vary considerably between fields; the provision of better field specific advice is restricted by our inability accurately to quantify this variability. The qualitative controls on the amount and timing of N release from ploughed grass are known, but better quantification of mineralization/immobilization over both the short‐ and long‐term and better understanding of the relationship with sward age, inputs and management are essential. Much N can also be released from pasture and lost to the environment, especially where long‐term leys have been grazed and there is a need to quantify the changing balance of mineralization and immobilization with the age of sward and N input. Whilst the overall principle of cultivation affecting mineralization is well known and appreciated, little is known about the mechanisms and quantification is only possible for a comparison of such extremes as ploughing and direct dri

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00963.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.To study the change in soil organic carbon (SOC) since it was recorded during the Belgian National Soil Survey some 40 years ago, we recently revisited 939 locations still under use as arable land. The study area comprised almost the entire province of West Flanders (about 3000 km2) characterized by profound changes in its arable land management.Taking the increased ploughing depth (by 9.8 cm on average) into account, a significant (P= 0.001) increase of the SOC content by 0.2% on average was found. Expressed as an amount, the SOC in the topsoil rose by 9.3 t/ha on average, representing an increase of 25%. This is comparable with the conversion of arable land into grassland for 2 to 3 decades.Geostatistical tools were used to map the SOC at the two times of observation. These showed that most of the spatial variation occurred within about 4 km. Since the community level is the smallest spatial resolution on which agricultural statistics are gathered officially, a detailed modelling of the change in SOC was impossible. However, by selecting communities with extreme changes in SOC, we found indications that the major source of increase in SOC was due to the large increase in pig breeding.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00964.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract.In response to the European Community Nitrate Directive (91/676) a catchment scale Geographical Information System (GIS) model of nitrate leaching has been developed to map nitrate vulnerability and predict average weekly fluxes of nitrate from agricultural land units to surface water. This paper presents a pilot study which investigated the spatial variability of soil nitrates in order to: (1) define an appropriate pixel size for modelling N leaching; (2) quantify the within‐unit variability of soil nitrate concentrations for pasture and arable fields; and (3) assist in the design of an efficient sampling strategy for estimating mean nitrate concentrations. Soil samples, taken from two 800 m transects in early September 1994, were analysed for water soluble nitrate. The arable soils had a mean nitrate‐nitrogen concentration of 0.693 μg/g (S.E. 0.054 μg/g) and the pasture soils had a higher mean nitrate‐nitrogen concentration of 0.86 μg/g (S.E. 0.085 μg/g). Spatial variability was investigated using variograms. The pasture data had a weak spatial relationship, whereas the arable data exhibited a strong spatial relationship which fitted a spherical variogram model (r20.87), with a range of 40 m. A pixel size of 40 m is suggested for nitrate modelling within the GIS based on the arable variogram and an improved sampling strategy for model validation is suggested, involving bulking sub‐samples over a 40 m grid for estimating mean nitrate concentrations in combined land use and

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00965.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00966.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book Review in this ArticlesSoil Conservation (Third Edition) By N. Hudson.Conserving soil resources: European perspectives. Selected papers from the First International Congress of the European Society for Soil Conservation Edited by R.J. Rickson.Soil and water management systems, 4th edition By G.O. Schwab, D.D. Fangmeier&W.J. Elliot.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1996.tb00967.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY