Sustainable Soil Use Research Articles

Measurement of N fluxes and soil N in two arable soils in the UK

We measured nitrate (NO− 3) leaching, ammonia (NH3), and nitrous oxide (N2O) emissions, denitrification, crop offtake of N, and wet N deposition on two fields at each of two sites for five seasons. The soils were loamy sand and silty clay loam. The objective was to quantify all the major N fluxes over 2 arable rotations on contrasting soil types and to assess the impact of these balances on soil N. The greatest N input was fertiliser-N, which was between 89 and 96% of the total, except when linseed was grown to which no fertiliser-N was applied. Wet N deposition was 7–15 kg ha−1 which contributed ca. 5% to total N inputs. Outputs of N were mainly as crop offtake and NO3 − leaching. Crop N offtakes were 54 to 98% of total N outputs, ranging from 45 kg ha−1 for linseed to 245 kg ha−1 for winter wheat. N offtake was usually least ( 200 kg ha−1) were usually by winter wheat crops when straw was removed. At both sites average leaching followed the expected pattern of sugarbeet < cereals < potatoes. Total annual losses of N2O never exceeded 2 kg ha−1 N, between 0.2 and 2.8% of fertiliser-N applications. Estimated losses of N2 gas tended to be greater, especially on the heavier soil, up to ca. 7 kg ha−1 in 1998/99. Fluxes of NH3 were usually small (1–3 kg ha−1 N), and nearly half of the measured fluxes were net deposition. Net N inputs of NH3 exceeded outputs in only one of the four fields monitored. Thus, the greatest potential reduction in N losses from arable fields not given organic manures is to minimise NO3 − leaching. This would have the additional benefit of reducing subsequent indirect emissions of N2O which at 2.5% of leached N, would be as great as direct soil emissions of N2O. However, it may be difficult to make significant reductions in leaching from rotations such as these, receiving only mineral fertiliser-N. Most crops in this study received no more fertiliser-N than was currently recommended at the time for optimum yield, and so reductions in N input would potentially have led to loss of income. Moreover, inputs and outputs of N were, at best, in balance and in one of the four fields monitored N outputs exceeded N inputs, which is likely to lead to a depletion of soil N. Any further decrease in soil N might have repercussions for the sustainable use of soil.

APPROPRIATE LAND USE PLANNING FOR SLOPE LAND IN TAIWAN

Thorough land use planning in a slope land watershed requires careful consideration of both natural and socialconditions. A modified simpleaccurate method was used to estimate a land use potential value for each terrain unit ofa slope land watershed in Taiwan. Soil loss estimates based on erosion modeling served as a guide for determining the mostsuitable land use type. The social feedback to the proposed land use planning was assessed through onsite interviews withthe land users. Results indicate large conflicts and differences between land use planning based on natural conditionevaluation and social needs. For sustainable soil and water resource use, land areas with moderate to high land use potentialvalue can only be released for human activities if adequate soil and water conservation practices are maintained. Land areaswith less than moderate land use potential should be kept in their original natural stage. This recommendation should greatlyimprove the soil and water loss problems in the study area and ensure future sustainable development of soil and waterresources in Taiwan.

ATTITUDES TOWARD SOILS AND THEIR SOCIETAL RELEVANCE: THEN AND NOW

Soils are relevant to society in diverse ways, supplying various economic and cultural services or functions as well as being the substrate for plants and a life-support system. Attitudes to the diverse kinds of soil resources and resulting land-use practices throughout human history indicate that mankind has frequently used other than the most fertile or easiest accessible soils. Many special techniques, such as terracing, have been developed to utilize and preserve less accessible land and shallow soil on slopes. Soil degradation and erosion following deforestation have frequently been a problem in the past, especially when some land was abandoned for cultural or economic reasons. Better data on current degree and extent of soil degradation are needed. Man has made soils fertile on a large scale, providing more secure food resources for the ever growing population. Yet, there is a growing threat to soils, in many instances, on marginal soils or in less resilient soil regions. A good environmental ethic requires equally good soil care of open spaces and of forests, woods, and deserts for better quality of life and for future generations of town and country populations. For this purpose an Eleventh Commandment was formulated a generation ago, and efforts are now being made to institute an internationally secured global treaty or soil convention for better soil care and sustainable use of soils. Soil scientists need to support such proposals and to bridge the gaps and differences between local and governmental efforts.

The relevance of the Rio-Convention on biodiversity to conserving the biodiversity of soils

Nowhere in nature are species so densely packed as in soil communities. A large number of animal phyla and a diverse microflora are represented and these comprise a considerable part of any country's biodiversity. There are three main reasons for protecting soil biodiversity, (i) Ecological reasons: Decomposition and soil formation are key processes in nature and represent `ecological services' for the rest of the ecosystem. Soil organisms also represent the base for several above-ground food chains and the majority of terrestrial insects are soil dwellers for at least some stage in their life cycle, (ii) Utilitarian reasons: Soil biodiversity form the basis of agriculture, some medicines, and research in ecology and other disciplines and (iii) Ethical reasons: All life forms can be said to have an inherent value. Many groups of soil organisms are very old in evolutionary terms. Soil biodiversity must be included in the national strategies for long-term preservation of biodiversity to be developed following the Rio-Convention on Biodiversity. This implies both pure conservation measures and sustainable use of soils. Conservation measures must include identification and protection of sites with unique, endemic or threatened soil communities. Other targets could be rare soil types or intact soil profiles. Soil biodiversity is generally high in forests which may represent `hot spots' in agricultural landscapes. Measures for sustainable use must aim at keeping the biodiversity of agricultural and forest soils as high as possible. Chemicals and other treatments, which reduce soil biodiversity, should preferably be avoided. Conservation of soil biodiversity is a new and challenging field, for soil biologists, conservation biology, and local, national and international authorities. There is a great need for strengthening both basic and applied soil biology, including taxonomy and soil biologists should start the process by publicising the role, great complexity and threats to soil communities.

Soil Erosion Impact on Agronomic Productivity and Environment Quality

Soil erosion is a global issue because of its severe adverse economic and environmental impacts. Economic impacts on productivity may be due to direct effects on crops/plants on-site and off-site, and environmental consequences are primarily off-site due either to pollution of natural waters or adverse effects on air quality due to dust and emissions of radiatively active gases. Off-site economic effects of erosion are related to the damage to civil structure, siltation of water ways and reservoirs, and additional costs involved in water treatment. There are numerous reports regarding the on-site effects of erosion on productivity. However, a vast majority of these are from the U.S., Canada, Australia, and Europe, and only a few from soils of the tropics and subtropics. On-site effects of erosion on agronomic productivity are assessed with a wide range of methods, which can be broadly grouped into three categories: agronomic/soil quality evaluation, economic assessment, and knowledge surveys. Agronomic methods involve greenhouse and field experiments to assess erosion-induced changes in soil quality in relation to productivity. A widely used technique is to establish field plots on the same soil series but with different severity of past erosion. Different erosional phases must be located on the same landscape position. Impact of past erosion on productivity can also be assessed by relating plant growth to the depth of a root-restrictive horizon. Impact of current erosion rate on productivity can be assessed using field runoff plots or paired watersheds, and that of future erosion using topsoil removal and addition technique. Economic evaluation of the on-site impact involves assessment of the losses of plant available water and nutrients and other additional inputs needed due to erosion. Knowledge surveys are conducted as a qualitative substitute for locations where quantitative data are not available. Results obtained from these different techniques are not comparable, and there is a need to standardize the methods and develop scaling procedures to extrapolate the data from plot or soil level to regional and global scale. There is also a need to assess on-site impact of erosion in relation to soil loss tolerance, soil life, soil resilience or ease of restoration, and soil management options for sustainable use of soil and water resources. Restoration of degraded soils is a high global priority. If about 1.5×109 ha of soils in the world prone to erosion can be managed to effectively control soil erosion, it would improve air and water quality, sequester C in the pedosphere at the rate of about 1.5 Pg/year, and increase food production. The risks of global annual loss of food production due to accelerated erosion may be as high as 190×106 Mg of cereals, 6×106 Mg of soybeans, 3×106 Mg of pulses, and 73×106 Mg of roots and tubers. The actual loss may depend on weather conditions during the growing season, farming systems, soil management, and soil ameliorative input used. Erosion-caused losses of food production are most severe in Asia, Sub-Saharan Africa, and elsewhere in the tropics rather than in other regions.