ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00475.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00476.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Dryland salinity in the Mt Lofty Ranges, South Australia has developed as a result of native vegetation being replaced with pastures that use less water. Groundwaters have risen and mobilized ions (sodium, chloride, sulphate and iron) stored within deeply weathered micaceous sandstones and schists. Salinity resulting from sodium chloride is common in agricultural catchments around Australia, but saline sulphidic soils (with sulphate and iron) have only been studied in South Australia. Salinity is also associated with waterlogging and secondary sodicity. The amelioration of dryland salinity and waterlogging involves management of whole catchments, not just the area that is currently saline. It is imperative that all processes operating in saline catchments and their interactions are clearly understood.Salinity, waterlogging, sodicity, sulphidization and water erosion were studied in four saline sub‐catchments in the Mt Lofty Ranges. Grey (bleached) and yellow mottles (iron depletions) or black and red stains (iron concentrations) develop under certain conditions of water saturation, salinization, sulphidization, sodification and water erosion in surface and subsurface horizons. The amounts of these diagnostic features were used to develop a farm planning key for managing saline catchments in the Mt Lofty Ranges. Using soil diagnostic features, soil‐water processes in saline catchments are easily identified by farmers and land managers. Management options (e.g. fencing, tree planting and drainage) are then targeted to specific soils and can be easily incorporated by agricultural advisers into farm management plans. We recommend that soil diagnostic features which help predict the onset of land degradation be used in the production of land capability maps for farm planning purpo

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Soils and land use in the Atlantic Zone of Costa Rica were mapped independently at a scale of 1: 100000. At this scale, mapping units are often composite, both in terms of soil type and land utilization type. Combinations of given soil and land utilization types were produced by overlaying the soil and land use maps, on which there was 63% coincidence of unit boundaries. Each combination of land unit and land use was evaluated in terms of bio‐physical potentials. From expert judgement land use was shown to be (a) in balance with the use potential, (b) exceeding the use potential (‘over‐use’) or (c) less than the use potential (‘under‐use’). 18% of the area is over‐used, in non‐sustainable forms of land use, but 51% is under‐used and could be put to more demandin

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The influence of conventional and soil‐specific management on leaching and runoff losses of soil‐applied alachlor (2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl) acetanilide) was studied across a soil catena (landscape) with varied slope and drainage characteristics. The catena consisted of: a well‐drained Ves (fine‐loamy, mixed, mesic Udic Haplustoll) soil on the backslope (1–4%), a Ves soil on the sideslope (6–12%), and a poorly drained Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soil on the toeslope (0–3%). In general, the concentration of alachlor in runoff water was greater in the Ves soil than in the Webster. In 1992 alachlor concentrations in runoff (water, sediment + water) were less for soil‐specific rates (2.20 or 2.80 kg/ha) than for a uniform rate (3.36 kg/ha) in both Ves soils. There was no significant difference in alachlor concentration related to application rates (soil‐specific rate 3.66 kg/ha) in the runoff from the Webster soil. Averaged across soils and events, the concentrations of alachlor in runoff (water, sediments + water) were less for soil‐specific rates than for the uniform rate. Alachlor was not detected in soil samples obtained from depths greater than 15 cm in any soil or treatment after the first sampling. At the first sampling in 1992 (7 days after application) alachlor was detected down to 45 and 90 cm in the Ves and Webster soils, respectively. Detectable amounts (≥0.1 μg/1) of alachlor were observed in soil water samples extracted from all three soils during some sampling dates. No particular trends were ob

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00479.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.The effect of ploughing on the vertical and horizontal distribution of137Cs was investigated at two fields in Bavaria from 1987 to 1991. Soil samples from four layers in eight plots along a transect were taken in each field after each ploughing and harrowing. Total activities and activity concentrations were evaluated separately for137Cs derived from Chernobyl and from global fallout of weapon testing. In 1987137Cs from global fallout was already well mixed in both fields because of the long residence time in the soil.137Cs derived from Chernobyl, however, was distributed rather inhomogeneously in vertical as well as in horizontal directions. The coefficient of variation of the vertical activity concentrations within the Ap horizon decreased continuously from the first to the fourth ploughing, in one field by a factor of five. The number of ploughings necessary to attain a uniform vertical distribution of Chernobyl‐derived caesium was three and four in the two fields. Along the transects inhomogeneities caused by the spatial variability of the deposition of radiocaesium during the Chernobyl fallout were not removed by ploughin

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00480.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Little is known about thein situhydrological properties of Zimbabwean soils. This paper describes the water retention and transmission properties of two agriculturally important Zimbabwean fersiallitic soils measuredin situby the instantaneous profile method. The first soil, typical of those used by small scale farmers, is a deep coarse grained granitic sand. The second is a silty clay loam derived from mafic rocks, typical of the red clays associated with Zimbabwe's commercial farming areas. TheK‐θ functions for each layer of the sand were very similar and the profile could be described by a single function, with permeability increasing with depth. In contrast, the silty clay loam could not be described by a single function, as permeability decreased with depth. However, in both soils water movement became negligible below a matric potential of—0.01 MPa; this is thought to be a more appropriate field approximation of the upper limit of plant available water than—0.033 MPa which is often used for tropical

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00481.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Studies have been made of the effects of 15 g N/m2as urea in two dressings during April and June on annual nutrient fluxes in runoff from reseeded blanket bog also receiving annually 6 g P/m2as granular superphosphate and 6 kg K/m2as potassium chloride. Urea applications increased significantly (P<0.05) the mean annual ammonium‐N flux from 17 mg/m2for the P + K plots to 245 mg/m2for the N + P + K plots. Annual fluxes of total P, K and Ca were also increased (P<0.05) by the addition of urea. This was attributed to the effects of increased acidity around grass roots following N uptake as ammonium‐N. In contrast, nitrate‐N was removed from rainwater throughout the year and concentrations in runoff were at the limit of detection (<0.01 mg/1) on many occasions. Concentrations of organic‐N in runoff exceeded those of ammonium‐N, but were not significantly changed by fert

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00482.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abstract.Biophysical and economic data from numerous sources are integrated using the ALES expert system. A systematic approach to data collection and evaluation procedure is presented. The collection of management data is emphasized if management and crop yield data are to be adequately correlated. Different land utilization types are evaluated for numerous land mapping units. The results show that direct comparison of land mapping units is possible both within and between different land utilization types. Use of the model enabled objective relationships to be developed between biophysical criteria, crop productivity and management, allowing economic measures of performance to be routinely determined for large databases. The study shows that land mapping units with the most favourable physical suitability class may not necessarily have the largest net return and that the best lands are determined not only by their ability to produce high yields but also their ability to achieve them at the least cost.

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00483.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0266-0032    

DOI:10.1111/j.1475-2743.1994.tb00484.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY