DINÂMICA DA DECOMPOSIÇÃO E LIBERAÇÃO DE NUTRIENTES DA PALHADA DE AVEIA PRETA E NABO FORRAGEIRO CORTADAS EM DIFERENTES ESTÁGIOS DE DESENVOLVIMENTO

The dynamics of nutrient (N, P, K, Ca and Mg) decomposition and release from winter litter mulching of black oat (Avena strigosa Schreb) and turnip (Raphanus sativus L.) were studied during a 8,5 month period. Factorial randomized blocks were used as the experimental design. A combination of the two mentioned soil mulchings cut at three development stages was used. These were: vegetative (94 days), flowering (103 days) and full flowering (116 days). Harvested material was put into small nylon bags that were scattered on the soil and recovered after five periods of four weeks each for content examination. Results were submitted to variance and regression analysis. Adjustment to a mathematical model indicating mass loss was made according to BADRE et alii, (1998). The experimental model relates the mass decomposition rate as well as nutrient release as a quadratic function on time (t). the mathematical model used was: M(t) = M(o). Exp. T (a t + b). The dry mass production presented no differences between species. It was higher under flowering and full flowering conditions when compared to the vegetative phase for oat as well as for turnip (p 0,05). The carbon/nitrogen (C/N) ratio and lignin, silica and cutin (ADF) were both different between the different phases (p 0,05). In terms of nutrient release the exponential model used was highly significant (p < 0,01) for all nutrients independently of the species studied and their development phases.