The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium-137 (137Cs) was used to quantify net erosion and net deposition within the landscape over a 3-yr period. Uneroded (native) sites were used to establish the mean background level of 137Cs in each of the study areas. The results indicate significant degradation of the non-renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a "bare' state and repeatedly tilled every second or third year. -from Author
Many of the soils in Santa Cruz Department, Bolivia, are degraded by serious weed infestation, subsoil compaction, and low organic matter and nitrogen contents. Fallow periods with cover crops are frequently used to recuperate the fertility of degraded soils, but little information exists on the desired characteristics of cover crops for this purpose. The aim of this study was to describe those characteristics, believed to be most relevant to the rehabilitation of degraded soils in Santa Cruz, of 14 cover crops, which included three grasses, nine legumes, and two winter cover crops sown after summer soybean (Glycine max). The cover crop characteristics, evaluated over two years, were ease of establishment, competitiveness against weeds, tolerance to drought, dry matter production and nutrient contents of the above-and below-ground residues, nodulation, rooting density and root diameters. The three grasses Tobiata (Panicum maximum var. Tobiatd), Centenario (Panicum maximum var. Centenario) and Brizantha (Brachiaria brizantha) appeared to be the most promising for increasing soil organic matter contents, and the three grasses and groundnuts (Arachis hypogaea)/pigeon pea (Cajanus cajan) for the recuperation of subsoil structure. Mucuna deeringiana and Lablab (Dolichos lablab) were the most promising for increasing soil N status. All of these cover crops competed successfully with weeds.
Australia's environments have been dramatically transformed by immigrant communities who were impelled by a simple utilitarian dream and obliged by geographical and historical circumstance to contend with accumulating uncertainties, including those connected with the operation of Nature's own independent dynamic. With the exception of a few critical junctures and significant but highly localized settings which are reasonably well supplied with primary material, the historical records are scarcely satisfactory for fine-textured reconstructions of changing physical landscapes. There is certainly some potential for very broad ‘indicative’ stocktaking, but unavoidable imprecisions and the irritating problem of discontinuities rule out the most ambitious of International Geosphere-Biosphere Programme (IGBP) style studies. Therefore a major premise of this discussion is the acceptance that we are obviously better placed to offer a range of underpinning social, political and economic analyses than to launch into the production of confident, large-scale reconstructions of the past ‘faces’ of Australia. The bulk of this paper explores that proposition and is confined to such analyses. On the other hand, it also suggests that the time is ripe for tailoring novel co-operative research into landscape change in the ‘European’ era, especially by combining physical and documentary evidence in the investigation of carefully selected sites and situations.
Concern for the better management of environmental resources grew during the 1980s. While this concern encompassed the misuse of the Third World's resources, those nations' governments and their peoples showed less awareness of the environmental damage being done in their quest for development. Environmental degradation has reached serious proportions in Algeria where oil wealth has masked failings of agricultural production and, together with industrialization, has provided a ‘veneer’ of economic development.
The vulnerability of Algeria's natural environment and the fragility of its ecosystems have been stressed by Cǒte (1983). Once cleared, Algeria's woodlands and forests are slow to re-establish and surface deposits are easily erodable. Soils were largely formed under past climatic conditions, and so cannot be restored naturally by present pedogenetic processes. Such an environment is difficult and delicate to exploit to any high degree of agricultural intensification and is under increasing demographic pressure. Culturally and organizationally the agricultural system is far from ideal if agriculture is to be sustained. Often in Algeria the highest rainfall falls on the steeper slopes while the gentler slopes receive insufficient for agriculture. Only 500 000 hectares out of Northern Algeria's 38–40 million hectares receive more than 600 mm of rainfall and have slopes of less than three per cent (Cǒte, 1983). As much as 20 million hectares of Northern Algeria were identified by Dregne (1983) as … ‘vulnerable to desertification’ with large areas falling into his ‘severe’ risk category.
This study seeks to demonstrate the dimensions of environmental degradation through observations and the monitoring (during the 1980s) of Algeria's media: largely newspaper and television reports. Particular emphasis is placed on the growing environmental ‘crisis’ since 1988. It should be stressed that the Algerian Government uses a controlled media to disseminate official information. Misuse and overuse of environmental resources have combined with inadequate government economic policies and a neglect of ecological issues to cause the ‘crisis’.
This paper examines soil amelioration by planting 15 leguminous and graminaceous plant species, including herbaceous annuals, perennials and biennials, and woody perennials and biennials. Disturbed and undisturbed natural regrowth were planted with leguminous species, in some cases with fertilizer applied at planting (400 kg ha−1 of 15:15:15 NPK). The studies were made on two highly degraded sites in southwestern Nigeria which had been subjected to intensive mechanized cropping for a period of 10 years. Changes in soil physical and chemical properties were monitored from 1989 to 1991. Acacia difficilis, Brachiaria lata and Mucuna utilis had the lowest survival rates by the following growing season. Soil fertility and compaction levels differed between sites. Planting had no effect on the latter. The decreases in compaction (i.e. macroporosity) between 0.00 and 0.10 m depth at both sites one month before and five and 17 months after planting were 43, 59 and 61 per cent, respectively were attributed to exclusion of heavy machinery from the sites. Large decreases in fertility occurred at both sites and were attributed to a combination of nutrient extraction and to leaching. Between fallow species, exchangeable Ca, pH and the cation-exchange capacity (CEC) were greater and total acids lower for herbaceous cover compared with woody perennials, and was attributed to a higher Ca demand by the latter. Highest and lowest values of Ca, CEC and pH occurred in plots where plant material was returned to the soil (i.e. by cutting or die-back) and in cropped plots, respectively. Natural regrowth was as effective or better than planted species in improving soil physical and chemical properties. Therefore the use of exotic plant species for ameliorating highly degraded alfisols is unnecessary. Amelioration of highly degraded alfisols may be best effected by allowing natural regrowth to occur while excluding all mechanized traffic from the site.
It is suggested that stopping liming on agricultural land could lead to a potential chemical time bomb (CTB). the sequence of interrelated events leading to the CTB include the end of liming, perhaps caused by a change in land use, a progressive decrease in soil pH and increased solubility of potentially toxic contaminants that accumulate in soils as a result of agricultural practices. Data are presented on rates of long-term soil acidification and modelled changes in the solubility of some trace metals in soil as a result of acidification. Soil acidification rates depend primarily on acid input rates and the soil's acid neutralizing capacity, possibly limited by neutralization kinetics. Experimental data illustrating this point show that the pH decreased rapidly in a field soil receiving ammonium rather than nitrate fertilizer treatment. on a limed agricultural field that was later abandoned and converted to deciduous woodland, The pH of the 0-23 cm soil layers decreased over 100 years from pH 7 to 4.2. Deeper layers acidified at a slower rate. Thermodynamic model calculations simulating the solubilities of metals in a sandy topsoil showed zinc, cadmium and aluminium solubilities increasing exponentially with decreasing pH, resulting in several-fold solubility increases between pH 5 and 4. These results suggest how metal solubility increases after liming stops. the model pH-solubility relationships depended on the type of metal, The solid phase controlling the solubility, and the amount of metal in the soil if adsorption controlled the solubility. Decreasing pH and the resultant increase in metal solubility expected on abandoned farmland might be managed through techniques such as liming or planting forests of selected tree species.
In the Gadarif Region of Sudan, destruction of the natural vegetation for agricultural expansion is one of the major causes of the degradation of renewable resources and the environment. This study identifies and analyses the farmers' attitudes and perceptions towards agricultural land degradation and abandonment. The cross-sectional data collected from ten key informants and 41 large-scale farmers focussed on the degradation and abandonment of mechanized agricultural land. The results of the study show that the respondents are well aware that soil degradation is in various forms are taking place on their cultivated agricultural land. This is based on their perception and interpretation of indicators such as weed infestation, poor soil fertility and soil compaction. Continuous cropping, mono-cropping, rainfall shortage and the use of inferior seeds are the main reasons of land degradation as indicated by farmers. The main measures acknowledged to maintain and improve land productivity are repeated soil ploughing, abandonment/fallow periods and crop rotation.
The study adduces evidence of widespread land degradation. The mitigation measures followed by the farmers may though not be sufficient to restore the soil fertility. The application of appropriate chemical fertilizers, sound crop rotation and long fallow periods can be recommended. Any management and research intervention regarding the problem of land degradation should; however, be concerted with the farmers' knowledge. Copyright
The environmental impact of recent changes in land use is assessed in a part of Andalucia, southern Spain, where the deintensification and abandonment of low productivity upland areas is taking place. In the uplands of the Alpujarra, the traditional landscape most at risk is that of the irrigated cultivation terraces. These have often been established centuries ago and rely on water abstracted from streams draining the southern slopes of the Sierra Nevada. The causes of this deintensification include labour shortages, with many Alpujarra municipios reporting population decreases of up to 50 per cent since 1950. Landsat Thematic Mapper digital data from May and August 1992 have been used to identify the various land cover components of the Alpujarra. Ground verification undertaken in September 1992 and April 1993 has confirmed that deintensification of terraced areas around the villages of Trevélez (at 1500m, the highest village in Spain) and Pórtugos (1300 m) can be identified as either grassland or matorral. It is recognized that many classes of land cover are mosaics with several elements at a subpixel scale (e.g. terrace risers with fruit trees). However, the output from image processing has allowed areal estimates of the main land covers representing deintensification within the terraced zone. The pattern of deintensification of terraced land is fairly complex. It can be assumed that all terraces were irrigated and cropped at some stage. Land which is no longer cropped is usually grazed and the invasion of matorral species is common, particularly when irrigation ceases. Unirrigated tree crops and vines are sometimes planted on terraces no longer used for cropping. A model of deintensification of farming on terraced land in the Alpujarra is presented.
This study aimed to determine microbial biomass carbon and microbial abundance immediately after, and two years after, forest soil erosion, so as to estimate the degree of damage, including the rate of recovery of microorganisms, in each area. It also aimed to determine the community diversity, and to establish relationships between microbial biomass, microbial abundance and the physico-chemical properties of the soil.
Three different study areas in Hiroshima Prefecture, Japan, were used. One undisturbed area and two eroded areas (one immediately after and one two years after erosion). The analysis of variance showed a highly significant difference in microbial biomass carbon and abundance between the study areas. The undisturbed area showed the highest value, followed by the area eroded two years ago, then lastly the area studied immediately after the erosion. The biomass carbon was highly correlated with gram positive bacteria with r2 = 0·983, p < 0·01. The biomass carbon and microbial population were shown to be significantly correlated to the soil's physico-chemical properties, such as pH, moisture content, water-holding capacity and CN ratio. However, CN ratio proved to be closely correlated to biomass carbon with r2 = −0·978, p < 0·01, to Gram-positive bacteria with r2 = −0·977, p < 0·01, to Gram-negative bacteria with r2 = −0·989, p < 0·01 and to fungi with r2 = −0·977, p < 0·01. The undisturbed area showed a highly diverse community in both of the restriction enzymes used, followed by the area affected by erosion two years ago, then the area immediately after erosion. Copyright
Throughout Rwanda, terracing was reintroduced in 1973 as the major conservation practice to minimize soil loss on its steep agricultural lands.1 Terracing has been partially successful in reducing soil losses resulting from nonchannelized runoff, the goal of this practice. However, because of the widespread fragile environmental conditions in the highlands, soil fertility has decreased and soil acidity increased in numerous fields as a direct result of the terracing. To maintain sufficient agricultural yields, within the constraints of a low resource agricultural system, farmers have responded to the acidity and soil fertility problems by systematically removing a portion of the terrace berm during field preparation. This practice, in response to the changing environmental situation due to terracing, results in significant amounts of soil displaced downslope year after year. This human-induced soil erosion process seriously counters many of the intended benefits of terrace construction and is contributing to the land degradation problem. The results of this study emphasize the need for both conservation strategies and the measurement of soil loss to be sensitive to human-induced as well as natural erosional processes. By not considering the human response to terrace construction, the benefits of this conservation practice have been seriously offset.
A field trial investigated the early performance of six tree species planted into an acidic minespoil ameliorated by ploughing or incorporation of 10 per cent by weight of pulverized fuel ash (PFA). Common alder, Italian alder and silver birch produced the greatest total shoot extensions for PFA-ameliorated minespoil. Rowan, sycamore and aspen were unsatisfactory for both ameliorative treatments. PFA increased the pH of the minespoil for a period of time potentially beneficial for the establishment of the tree species. For the rate of PFA application studied, general salinity effects and cold-water-soluble boron both presented problems for successful tree growth.