DECOMPOSITION OF CROP RESIDUES UNDER LABORATORY CONDITIONS

A laboratory study was designed to provide data on the decomposition o f rape, sunflower and soyabean residues put in bags buried in soil. Th e residue bags were removed at intervals during 1 year, analysed for r emaining total mass, organic and water-soluble C, water-soluble sugars , as well as for volatile acids and phenolic compounds. The decomposit ion dynamics of total mass, total organic and water-soluble organic C, and water-soluble sugars were reproduced satisfactorily by a double-e xponential model of the first-order type. Generally, no large differen ces in the rate and magnitude of decomposition among the residues were observed; the greatest losses of both total mass and chemical compone nts occurred in the first month of the study, during which the volatil e acids and phenolic compounds disappeared almost completely. Of the t hree residues, soyabean showed the lowest loss of organic carbon, losi ng 66% of the original content over the course of the year compared wi th 73 and 75% for sunflower and rape, respectively.