摘要:

Abstract.Despite a growing awareness that erosion on arable land in Britain is a potential hazard to long‐term productivity, there is still only limited information on the rates involved, particularly long‐term values. Use of the caesium‐137 (137Cs) technique to study soil erosion within arable fields on various soil types at 13 locations in southern Britain has yielded retrospective measurements of the long‐term (c.30 years) rates of soil loss and the patterns of soil redistribution within the study fields. The range of long‐term rates of net soil loss extends from 0.61 per hectare per year on clay soils in Bedfordshire to 10.5 t per hectare per year on brown sands in Nottinghamshire. The measured rates are compared with other published data for similar soil types and land use, and the implications for long‐term productivity and potential environmental impacts are

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.A method is presented for compiling a manual for the estimation of crop residue cover in the field. The crop residue is a combination of standing stubble and the straw remaining on the ground after harvest. Field assessment of crop residue is important so that management decisions may be made in the field. Such decisions include selection of cultivation or sowing machinery, irrigation scheduling (for crusting materials), soil temperature control and grazing of crop residue. The manual consists of a graded set of colour photographs, taken from an overhead boom, and a sampling rate nomogram to determine the number of 1 m quadrats required in a given field to estimate the cover with a predetermined level of error. Two methods for calibration of the photographs are compared: (a) projection of slides onto a screen with manual counting, and (b) digital image analysis of the photographs. Image analysis is efficient, rapid and gives less error than counting from the projections because many more points are counted. The use of the manual in the field is described. It is an inexpensive piece of equipment for the field agronomist or farmer, and gives a reliable, rapid and semi‐quantitative estimate of residue cove

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00871.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Microbial biomass C and P were monitored in the Oh horizon of an afforested podzol in Mid‐Wales before and after clearfelling. Measurements over a 2‐year period indicated that soil moisture and temperature control the seasonal fluctuations in biomass C in this soil. Clearfelling significantly increased biomass P in the Oh horizon. This was probably caused in part by increased fluxes of organic and inorganic phosphorus from the felling debris and litter horizons of the forest fl

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00872.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Field investigations on loamy sand soil showed that compaction by cattle trampling increased soil bulk density and cone penetrometer resistance. Trampling produced very dense zones at depths of 7–10.5 cm, which impeded drainage, despite the presence of large macropores. Soil structural and hydrological changes caused by hoof compaction can result in serious pasture management problems. Compaction simulation experiments on saturated turf indicated that most severe structural damage occurs on initial compactio

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00873.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Crop growth on strongly weathered soils is often limited by soil compaction in addition to aluminium toxicity and/or calcium deficiency. This study examines the effects of subsoiling, lime and gypsum on penetrometer resistance, acidity, aluminium and calcium levels and cotton (Gossypium hirsutumL.) root growth on soils transitional between Cecil and Appling series (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont region of Georgia, USA. The main plots were subsoiled to depths of 0.35 or 0.80 m or untreated. Dolomitic limestone (0 or 4.03 t per hectare on subplots) and phosphogypsum (0 or 10 t per hectare on sub‐subplots) were incorporated into the surface soil (0.15 m). Deep subsoiling (0.80 m depth) decreased penetrometer resistance at 0.3–0.5 m depth and increased yield in two of three years, but there was no response to shallow subsoiling (0.35 m depth). Lime increased yield when surface soil water pH prior to amendment was less than a Cate‐Nelson critical value of 4.6. Gypsum moved downward much more rapidly than lime, increasing soil solution calcium ion activity to a depth of 0.8 m within 5 months of application. There were differences in clay content between replicate plots and calcium movement was faster where the clay content was less. Yield responses to gypsum in 1986 were attributed to increased root growth below 0.2 m resulting from the increased calcium ion activity. Yield response to gypsum in limed sub‐subplots was significant only

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00874.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Concentrations of soil nitrate were measured in areas of different land use within a small drainage basin. From previous work on nitrate losses from subcatchments, soil nitrate levels were expected in the order arable>grassland>woodland. Although differences were detected, they were not consistent and seasonal variations in soil nitrate for the same land use were greater than those between land uses. Seasonal fluctuations in stream nitrate loads were not strongly related to the seasonal differences in soil nitrate levels but were more closely related to stream discharge and antecedent climatic conditions. Losses of nitrate from the catchment seemed to be transport limited and independent of variations in soil nitrate supply; the implication is that water quality control by land use manipulation will only be successful in supply limited situations when leaching losses are sensitive to variations in soil nitrate supply.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00875.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Geostatistics is basically a technology for estimating the local values of properties that vary in space from sample data. Research and development in the last 15 years has shown it to be eminently suited for soil and ripe for application in soil survey and land management. The basic technique, ordinary kriging, provides unbiased estimates with minimum and known variance. Data for related variables can be incorporated to improve estimates using cokriging. By more elaborate analysis using disjunctive kriging the probabilities of deficiency and excess can be estimated to aid decision.The variogram is crucial in all geostatistics; it must be estimated reliably from sufficient data at a sensible scale and modelled properly. Once obtained it can be used not only in the estimation itself but also to choose additional sampling sites, improve a monitoring network or design an optimal sampling scheme for a survey. It may also be used to control a multivariate classification so that the resulting classes are not too fragmented spatially to manage.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00876.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Experiments were conducted for one year on two different soil types. On a clay soil straw was either (a) burnt, (b) baled leaving the stubble, or (c) chopped and spread. The soil was tine cultivated to depths of 5, 10 or 15 cm or ploughed to 20 or 30 cm before winter wheat was sown conventionally. In addition, a direct‐drilled crop was sown after each straw treatment. On a silt loam soil the direct‐drilled, tine cultivated to 15 cm and ploughed to 30 cm treatments following burning or chopping and spreading straw were repeated.Tine cultivation incorporated less straw than ploughing, decreased plant establishment and early growth but did not decrease yield. Direct‐drilling through chopped straw decreased yield on the silt loam but not on the clay soil. Short straw (<5 cm) was easier to incorporate than longer straw. Ploughing was the most efficient method of straw incorporation because it inverts soil. Early effects on crop growth and nutrient uptake following straw incorporation were transient and associated with large amounts of straw in the seeded layer of

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00877.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Soil has a finite strength to resist permanent volume change and permanent shear deformation. When the stresses imposed on the soil are of a sufficient magnitude to overcome the strength, then the deformation falls into one of two regimes. At low stress ratios (ratio of normal stress to maximum past stress) the soil expands when sheared and at high stress ratios it compresses. The maximum past stress in a field soil is the pre‐consolidation stress. The pre‐consolidation stress is the compressive stress greater than which compression is considerable and permanent.These regimes of soil deformation behaviour are consistent and predictable under a wide range of conditions. They are described by the critical state concept, which can usefully be applied to soil management. Management decisions can be based on whether the stresses imposed by a particular operation result in high or low stress ratios. This governs whether the soil will deform permanently or not (for compaction damage), expand on shear (tillage) or compress on shear (preparation of rice paddy soils). The change in permeability and structure can also be predicted from the deformation reg

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00878.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The influence of three urease inhibitors, hydroquinone (HQ), phenyl phosphorodiamidate (PPDA) and N‐(n‐butyl) phosphorothioic triamide (NBPT) on denitrification of nitrate in soil was studied in an incubation experiment under waterlogged conditions, at 25°C and in the presence of increasing amounts (0.0, 0.1 and 1 %) of ground barley straw. Two hundred milligrams of nitrate‐N (as potassium nitrate) was added with the respective urease inhibitors.Addition of barley straw increased the denitrification rate in the soil. Within 2 days the added nitrate‐N was completely reduced. This result was confirmed by the measurement of nitrous oxide. HQ decreased gaseous nitrogen loss by decreasing the activity of the denitrifiers in the soil. The inhibitory effect was increased by adding increasing amounts of HQ. Because denitrification is stimulated by readily decomposable organic matter, the retardation seems to be a short‐term effect. The other urease inhibitors, PPDA and NBPT, had no significant influence on the denitrification process when they were applied at the rate of 4 mg per kilogr

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1991.tb00879.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY