The objective of this work was to evaluate the rate of decomposition and rate of release of macronutrients and Si in the biomass from intercropped sunn hemp and millet, as a function of time after management, both with and without fragmentation. The experiment was conducted under field conditions in Botucatu, S?o Paulo. The experimental design was of randomized blocks with four replications, in a factorial design consisting of two managements of shoot phytomass (with and without mechanical fragmentation) at six harvesting times [0, 18, 32, 46, 74 and 91 days after management (DAM)]. The dry-matter weight, macronutrient and Si content, and quantity of remaining nutrients were determined. The data were subjected to variance analysis, the averages of the factor management treatments were compared by t-test (LSD) at 5%, and those of the factor sampling-times, adjusted to the mathematical equations. Fragmentation of the phytomass increases the rate of decomposition and release of N, P, Ca and S. K is available quickly, with on average 1.5% of the total amount accumulated at 91 DAM. By 91 DAM at least 80% of all the macronutrients had been released into the soil. The maximum daily release of macronutrients occurs between 0 to18 DAM. The release rate of Si is constant, and there is an increase of the content of this element in the phytomass over time, due to the marked release of C. The element Si is that released most slowly into the soil, with there still being present at DAM 91 on average 85% of the total amount accumulated in the phytomass.
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