EFFECT OF INCORPORATION DEPTH AND SOIL CLIMATE ON STRAW DECOMPOSITIONRATE IN A LOAMY PODZOLUVISOL

Several studies on the decomposition of straw using the mesh bag techn ique were carried out under field conditions in south Estonia. Straw o f spring and winter cereals (Hordeum vulgare L., Secale cereale L., Tr iticum aestivum L.) was compared over different periods and at two dep ths (5 and 20 cm). Calculation of straw decomposition was based on the ash-free organic matter weight loss. Depending on experimental and cl imatic conditions the decomposition rate fluctuated from 42% to 75% du ring the Ist year. The three experimental factors incorporation period , incorporation depth and straw species all had a significant effect o n the decomposition of straw. The decaying processes proceeded more ra pidly in the upper layer and during the initial months; later there we re no differences in decomposition rate between the two depths. During the period without vegetation, i.e. from freezing (December) to thawi ng (April) of the soil, the decomposition rate was 6-7% and during aut umn it was about 10%. Greater loss of straw occurred early in the grow ing season and in the upper layer. The release of nitrogen from straw was slow and N quantity in straw increased due to microbiological immo bilization during the 1st year.