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Results of field experiments with soil compaction induced by wheel traffic applied uniformly to cover the entire surface of the experimental plots are reported. Compaction was done immediately before sowing, and each year, in each location, the same treatments were repeated on the same plots. The number of tractor passes varied between 0 and 30. The experiments were conducted during the 1978–1981 period in four locations with different soil and climatic conditions.Changes in soil physical properties, as well as in the yield of maize grain, were shown to be related to the number of tractor passes according to regression formulae of the type: Y = aXb. Most of the changes were recorded between 0 and 8–10 passes, while with more than 15–20 passes changes became negligible. The average maximum increase in bulk density was 20–25% as compared with the non-compacted control plot, and the average maximum decrease in yield was 46%. Moisture content in the compacted control plot, and the was 2–3% (w/w) lower than in the control plot, except for the soils with poor drainage where the lower part of the compacted topsoil showed an increase in moisture content. Air content in the compacted plots often dropped below 10, and occasionally to nearly 0% (v/v). For three of the four locations, grain yield of maize linearly decreased by 13 kg ha?1 (or 0.18% of the control plot yield) for each 1 kg m?3 increase in bulk density.  相似文献   
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Prediction of soil strength of arable soils and stress dependent changes in ecological properties based on soil maps Based on a database of at present 160 mechanical soil profile datasets, the site and horizon dependent mechanical soil strength expressed as precompression stress can be predicted by multiple regression analysis and used for documentation in maps at different scales. Stress dependent changes in air permeability or air capacity can be derived for the virgin compression stress range as well as the effect of stress propagation in soils or stress attenuation capacity and depth dependent changes of ecological properties. Thus, areas with defined mechanical sensitivity as a function of depth can be derived and recommendations for site adjusted farming techniques can be given. In addition it allows the agricultural machine industry to develop site adjusted machines to support the ideas of good farming practice, defined by the soil protection law of Germany.  相似文献   
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Even if it is less polluting than other farm sectors, grape growing management has to adopt measures to mitigate greenhouse gas (GHG) emissions and to preserve the quality of grapevine by-products. In viticulture, by land and crop management, GHG emissions can be reduced through adjusting methods of tillage, fertilizing, harvesting, irrigation, vineyard maintenance, electricity, natural gas, and transport until wine marketing, etc. Besides CO2, nitrous oxide (N2O) and methane (CH4), released from fertilizers and waste/wastewater management are produced in vineyards. As the main GHG in vineyards, N2O can have the same harmful action like large quantities of CO2. Carbon can be found in grape leaves, shoots, and even in fruit pulp, roots, canes, trunk, or soil organic matter. C sequestration in soil by using less tillage and tractor passing is one of the efficient methods to reduce GHG in vineyards, with the inconvenience that many years are needed for detectable changes. In the last decades, among other methods, cover crops have been used as one of the most efficient way to reduce GHG emissions and increase fertility in vineyards. Even if we analyze many references, there are still limited information on practical methods in reducing emissions of greenhouse gases in viticulture. The aim of the paper is to review the main GHG emissions produced in vineyards and the approached methods for their reduction, in order to maintain the quality of grapes and other by-products.  相似文献   
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