The effect of woody material incorporation on the evolution of chemical properties of soil and on plant growth

Bark and pig manure were incorporated in soil every 2 yr from 1982 to study their effects on cereal and forage yields and on soil chemical properties. Bark incorporation induced an intense nitrogen immobilization in soil. Consequently yields and nitrogen uptakes by plants were very low in 1982 on bark treatments, but significantly higher in the following years (1983–1985), more especially when bark and pig manure were applied together. Nitrogen immobilization was less intense at the second bark application. Plants may therefore absorb the remineralized soil nitrogen from the early fixed nitrogen during the initial bark decomposition. Soil analysis showed an increase of C:N ratios mainly in bark-amended soils. These C:N ratios ranged from 19 to 21 for control and bark treatments, respectively. In the course of 4 yr, the organic matter content on the < 2 mm fraction increased very slowly, although significantly at P = 0.05 where bark and pig manure were applied together. However, no cation exchange capacity change in soil has yet been observed. In the short term, bark alone decomposed very slowly in soil, and nitrogen immobilization effects still persist. Pig manure applied with bark increased its decomposition and humification, characterized by low optical ratios (E4:E6) of 5.4 to 5.0 compared to control and bark treatments with E4:E6 > 6. Bark application to soil, together with pig manure as nitrogen source, may improve long-term soil productivity. Key words: Bark, organic matter, decomposition, humification, immobilization, CEC