Results of a 35-year ploughless tillage experiment at Changins (1970-2004). Part II: Physical and chemical soil properties | Resultats de 35 ans de culture sans labour a Changins. II. Evolution des proprietes du sol

A tillage experiment was set up in 1969 at Changins to investigate the long-term effects of different ploughless tillage treatments. A crop rotation of winter wheat, winter oil seed rape, winter wheat and maize was grown on a clay humic soil and on a loamy soil. Three ploughless techniques were compared with conventional mouldboard ploughing: deep cultivation with a chisel plough (25-30 cm depth), shallow cultivation with a cultivator (10-15 cm) and minimum tillage with a rotary harrow (5-7 cm depth)instead of the minimum tillage, direct drilling (wheat and rape) and strip tillage (maize) were occasionally performed. In addition to the main treatments, the effect of subsoiling, reinforced nitrogen fertilization and straw incorporation have been observed sequentially. The repartition of available P, K and Mg in the soil depth showed some differences depending on the tillage system but without any influence on crop development. No systematic differences did occur between the mineral nitrogen level in the soil and the tillage treatments. Cropping methods leaving crop residues on the soil surface bring a slightly lower pH value to the soil. Conservation tillage – especially minimum tillage, direct sowing, strip tillage and to some extend tine tillage – enables a lasting preservation of the organic matter level in the upper soil layer. Organic carbon sequestration in the climatic and pedological conditions of our trial seems not to be realistic. The protecting effect of a crop residues layer on the surface may inhibit the soil drying and thus delay the installation of the new crop. Soil bulk density and total porosity have not been influenced systematically by the tillage treatments. However macroporosity may drop under the critical level of 10% in the ploughless treatments. The stability of the soil aggregates is systematically better in ploughless systems and soil resistance to penetration is higher. Water storage capacity is in inverse proportion to tillage intensity: the highest capacity characterises the minimum tillage which shows the poorest drainage capacity for rainwater. In a global evaluation on the long term effects of some tillage techniques on soil chemical and physical properties, ploughless tillage shows undeniable advantages. The most important are conservation of organic matter, improvement of soil stability and reduction of erosion risks. Nevertheless in some particular conditions the plough keeps the advantage. Experiences collected from other trials have shown that a pragmatic application of ploughless or plough depending on the local conditions and opportunities leads to an efficient and durable soil management.