Mineralization of organic materials in a calcareous soil

Abstract

The mineralization of an organic fertilizer mixture of grape debris and peat, pig and chicken manure, city refuse, aerobic and anaerobic digested sewage sludges added to a calcareous soil with low organic matter content was studied immediately after these additions, after they had decomposed for 6 months in the soil, after a maize harvest, and after a subsequent barley harvest. The organic materials were heterogeneous in their transformations in the soil: chicken manure and city refuse were the most easily mineralizable materials, while the pig manure and the organic fertilizer exhibited the lowest values. With the exception of pig manure, the materials experienced their major degradation during the first 6 months and became far less biodegradable after this period. In the mineralization process an initial stage was observed in which the amounts of carbon lost were highest, corresponding to the onset of microbiological activity in the soil and to the degradation of the easily metabolizable compounds, and final stage, in which there were almost constant daily losses of small amounts of carbon. According to the rates of global and complementary mineralization, the materials under study could be classified in three well-defined groups: the first, made up of city refuse and chicken manure, with high values of these rates; a second group, comprising the aerobic and anaerobic sewage sludges, with intermediate values; and a third group, with quite low values, formed by the organic fertilizer and pig manure.