01744naa a2200193 a 450000100080000000500110000800800410001910000160006024501200007626000090019652011720020565000190137770000190139670000160141570000160143170000160144770000190146377300680148218357292013-09-09       1984    bl ---       0--  u    #d1 aSTENGEL, P.  aFactors influencing the variation of some properties of soils in relation to their suitability for direct drilling.  c1984  aSoils from fifteen field experiments in the United Kingdom and one in France that compared direct drilling with mouldboard ploughing were examined with respect to their composition and physical properties. Indices of the stability and shrinkage of soil aggregates were obtained by measurement and an index of compactability was derived from an established relationship. It was hypothesized that these properties were possible determinants of soil responses to zero-tillage. Aggregate stability and shrinkage were correlated with organic carbon and clay content, respectively. Organic matter contents were greater at the surface of direct-drilled soils than in the complete topsoil layer after direct drilling or ploughing. In some cases the increase in organic matter significantly improved the physical properties of the soils. The three indices, of stability, shrinkage and compactability, were each ranked in high intermediate or low groups, and the soils classified according to their ratings in these groups. The resulting classification broadly agreed with a previous one of soil suitability for sequential direct drilling mainly based on experimental agronomy.  aPlantio Direto1 aDOUGLAS, J. T.1 aGUÉRIF, J.1 aGOSS, M. J.1 aMONNIER, G.1 aCANNELL, R. Q.  tSoil & Tillage Research, Amsterdamgv. 4, n. 1, p. 35-53, 1984.