Research Institute for Organic Agriculture, Frick

Influence of composts and digestats on soil fertility

In order to estimate the potential of Swiss composts to influence soil fertility and plant health, one hundred composts representative of the different composting systems and qualities available on the market were analyzed. The nutrient content of the composts was predominantly influenced by the materials of origin. The organic matter content, respiration rate and enzyme activities decreased when the composts become more mature. The N-mineralization potential of compost added to soil showed that a high proportion of young composts immobilized the nitrogen in the soil. The NO3-content of the compost allows it to predict the risk of nitrogen immobilization in soil. The phytotoxicity of the composts varied very much even in mature composts, showing that the storage of the compost plays a decisive role. While the majority of composts protected cucumber plants against Pythium ultimum, only a few composts suppressed Rhizoctonia solani in basil; the management of the maturation process seems to play a major role here. In field experiments, some biologically immature composts immobilized nitrogen in soil and reduced growth of maize. With additional fertilization, however, it was possible to compensate this effect. Digestats and composts increased the pH-value and the biological activity of soil. These effects were still observable one season after compost application.

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