ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00894.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The production of pigs in outdoor units is gaining in popularity in the United Kingdom and is often concentrated on free‐draining soils over important aquifers. Originally, stocking rates were sufficiently low to ensure the maintenance of a grass crop, but recently they have increased. Pigs are natural ‘rooters’ and wallowers and so cause damage to vegetation and soil structure. With overstocking these natural activities lead to considerable areas of bare, uncropped ground for much of the year. This paper assesses the potential for leaching of nitrate from such land, and makes recommendations for decreasi

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00895.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Two experiments on the same site in different years compared the effects of different intensities of deep loosening on soil properties and crop yield. Both experiments included subsoiling and one experiment, with potatoes, also included double digging and a comparison of conventional and zero traffic. The site was in a moist climate area (S.E. Scotland) on an imperfectly drained Gleysol with a clay loam subsoil. Cone resistance, soil water content and potential, bulk density and crop yield were measured to assess the effects of the treatments. Subsoiling did not loosen the soil very effectively because the subsoil was wetter than the plastic limit at the time of cultivation, even though the growing season prior to subsoiling was drier than average in both years. Double digging was more effective than subsoiling. Zero traffic gave a large yield benefit, especially when combined with double digging. There was no crop response to deep loosening in the presence of conventional traffic. Deep loosening had little effect on the drainage status of the topsoil.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00896.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The water contents of a restored and an undisturbed soil were monitored over two ‘dry’ growing seasons in order to examine the differences in crop water availability from different horizons. Bulk density was approximately 10% greater in the topsoil of restored land than in undisturbed land, and the water holding capacity was less, probably because there was less organic matter. In the subsoil a major problem was the inability of the soil to allow winter rainfall to recharge the water reserves. Bulk density and penetration resistance were greater in the restored subsoil than in the undisturbed subsoil. Increases in penetration resistance on drying may have restricted rooting activity, especially in the restored subsoil.Ripping of the subsoil to a depth greater than the usual 0.5 m, possibly early in the year in a grass crop to allow new root growth to exploit the cracks, may increase water availability for future dry seas

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00897.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Spatial averaging of data before or after modelling has important implications for large area land evaluation studies. Two procedures are evaluated for the spatial averaging of weather and soil moisture data before and after modelling (procedures A and B, respectively). The Thiessen polygon weighting technique is applied to a network of weather stations to derive daily weather values for the period 1955 to 1985 for 12 selected Agroecological Resource Areas (ARAs) on the Canadian prairies. These values are used in the model for procedure A. The components of the soil moisture balance for spring wheat are estimated with a budgeting model, assuming wheat is grown continuously for 30 years on soils with available water‐holding capacities (AWCs) of 150 and 250 mm. In procedure B, the data from individual stations are used as input to the model and the same Thiessen polygon weighting coefficients are applied to the output variables. A comparison of the two procedures shows no significant difference for temperature‐related variables such as frost dates, harvest date and cumulative potential evapotranspiration. The differences for moisture‐related variables (soil moisture content at sowing, cumulative actual evapotranspiration, runoff and deep drainage) are often statistically significant, but the absolute differences are less than 10 mm at probability levels ranging from 10 to 90%. For many practical applications the two procedures give similar re

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00898.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Qualitative and quantitative physical land evaluations differ in their technical procedures, i.e. use of expert knowledge versus process‐orientated simulation models. This paper compares the results of both procedures using the growth potential for sugar‐beet in the European Community. Qualitative procedures give suitability expressions, such as land being well suited or moderately suited for a given land use. Less than 30% of EC land was found to be well suited or moderately suited under water‐limited conditions. No quantitative expressions for the crop yield potential are, however, produced. The quantitative procedure describes suitability in terms of average crop yield and its temporal variability. Water‐limited and potential dry matter yields of sugar‐beet were estimated to range from 3.5 to 20 t/ha, and from 6 to 25 t/ha, respectively.Comparison of results of the qualitative and quantitative procedures for regions showed that the suitability classes obtained by the former can be characterized by different yield distributions derived from the latter. These yield assessments showed that results of qualitative land evaluation procedures aimed at assessing yield potential are meaningful only when they are linked to agroclimatic zones. The comparison also showed that some moderate restrictions, which often can be counteracted by adequate farm management, are not incorporated into the quantitative

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00899.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.A computer‐based land evaluation information system (MicroLEIS) was developed for optimal use of agricultural and forestry land systems under Mediterranean conditions. Through an interactive procedure several land capability, suitability and yield prediction methods may be applied. The system addresses land evaluation at reconnaissance, semi‐detailed and detailed scales in an interrelated manner. Biophysical land evaluation methods are incorporated using empirical, scale‐appropriate models, which range from purely qualitative (reconnaissance) through semi‐quantitative (semi‐detailed) to quantitative (detailed). This software is helpful for teaching, research and development, predicting appropriate agroforestry land uses. Its use is illustrated by an example.MicroLEIS runs on IBM PC, XT, AT, or a compatible microcomputer with at least 128 kilobytes of RAM and a PC‐DOS or MS‐DOS version 2.0 or later operating system. The software package on double or high density diskettes can be obtained from the

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00900.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.Changes in chemical and physical properties and erodibility of a vertisol were studied in relation to land use. The vertisol, which occurs extensively in the semi‐arid south‐east of Zimbabwe, is derived from basalt and has a self mulching surface layer. Irrigated crops show static yields despite introduction of improved varieties. Four uncultivated sites were selected as controls and compared with five irrigated and four dryland sites. Surface soils were analysed for a range of chemical and physical properties, and laboratory rainfall simulation was used to measure soil erodibility under high intensity rain. The irrigated soils had greater exchangeable sodium and available phosphorus than the uncultivated soils. In contrast, dryland soils showed no such changes apart from a decrease in the amount of small water‐stable aggregates. The soils are very erodible under high intensity rain but no significant differences were found between sites. We conclude that, although soil chemical changes have taken place in the irrigated soils, significant soil degradation has not occurred at the sites examined. The static yields probably result from management problems. However, immediate measures should be taken to improve drainage and irrigation management in the irrigated soils to avoid further sodium incr

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00901.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The area covered per unit mass (Am) of a mulch material is an important factor for controlling erosion, especially in the humid tropics. Values of Am for mulching materials commonly available in S.E. Nigeria ‐ guinea grass, banana leaves and palm leaves ‐ were found to be 0.00035, 0.00038 and 0.00020 haAg, respectively. These values are within the range (0.0001–0.0007 ha/kg) reported for other mulching materials elsewhere. They can be fitted into existing equations to determine the amount of mulches required to achieve any predetermined ground cover perce

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00902.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract.The soil water regime was monitored at a forested experimental site in Cumbria, UK. Over an 83‐week period following the clearfelling of 35‐year‐old Sitka spruce, soil water level measurements were related to total weekly rainfall in drainage treatment plots (10, 20 and 40 m ditch spacing) in three replicate blocks. Analysis showed a block × treatment interaction which might be related to soil differences between blocks. Significantly deeper soil water levels were measured in the most intensively drained plots of the two gently sloping blocks on a peaty gley soil. Drainage intensity had no effect on soil water level in the third block situated on a surface‐water gley soil on a ste

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1992.tb00903.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY