Results of a long-term experiment with different organic fertilization systems | Efficacite de differents apports organiques et d'un engrais mineral azote a Changins (1976-2004)

The efficiency of nitrogen and the effect on soil organic matter of different organic fertilizers combined with increasing mineral nitrogen levels have been investigated during a long term experiment at Changins. The grain yields of the Green manure treatments and the incorporation of Cereal residues are slightly lower than those of the Mineral fertilizers reference treatment. The grain yields of the Solid farm manure and Liquid farm manure treatments are higher than those of the Mineral fertilizers reference at low mineral nitrogen ratesat higher rates, differences between the organic matter management systems are not significant. Increasing mineral nitrogen fertilization enhances the organic matter content of the soil. The restitution of cereal crop residues is favourable to the organic matter level of the soil. High rates of solid or liquid farm manure significantly enhance the organic matter content of the soil. Ranging the organic fertilization systems on the base of their humus balance leads to following list: Mineral fertilizers Green manure Cereal crop residues incorporated Solid Farm manure 35 t/ha/3 years Liquid farm manure 60 m3/ha/3 years Solid Farm manure 70 t/ha/3 years. The best nitrogen efficiency rates are reached at about 2/3 of the normal mineral N fertilization level according to fertilization guidelinesrates are varying from 39.7 to 46.1%. The organic input by Green manure or Cereal crop residues reduces mineral nitrogen efficiency through nitrogen immobilization. Average nitrogen efficiency of farm manure confounding all crops varies from 14.1 to 19.7% with Solid farm manure treatment 35t/ha/3 years, from 11.5 to 16.6% with Solid farm manure treatment 70t/ha/3 years and from 14.7% to 22.6% with Liquid farm manure treatment 60 m3/ha/3 years. The residual effects of Solid farm manure and Liquid farm manure treatments is perceptible on the nitrogen exportation of the two crops following the interruption of any organic fertilization. In the absence of farm manure, the systematic restitution of crop residues or green manure cultivation is not sufficient to maintain the organic matter level in the soil. Reduction of soil tillage intensity is necessary as a complementary technique.