Long-term effect of organic fertilizers on soil properties

Consequences of the use of different organic fertilizers (green manure, cereal straw, manure at 35 and 70 t ha-1 every 3 years and cattle slurry at 60 m3 ha-1 every 3 years) and mineral fertilizer (four doses nitrogen) are tested in Changins since 1976. This study analyses their long-term effect on organic, chemical and biological soil properties. After 34 years of trial, when crops receive optimal nitrogen fertilizer, the soil organic matter (SOM) content decreases 0,50 g/100 g of soil for the treatment «mineral fertilizer», 0,20 g/100 g for the treatments «greenmanure » and «straws» and 0,18 g/100 g for the treatments «manure 35 t ha-1 every 3 years» and «slurry 60 m3 ha-1 every 3 years». Only the treatment «manure 70 t ha-1 every 3 years» shows an increase in the SOM content of 0,15 g/100 g. Organic fertilizers do not significantly affect the main soil chemical properties, except for trace element contents. The treatments receiving manure and cattle slurry present higher amounts of copper, iron, zinc and manganese extractable in ammonium acetate EDTA than the control «mineral fertilizer». Organic fertilizers have also a positive significant effect on the activity and microbial biomass and seems to change the composition of this last.