In São Paulo State, the autumn - winter seasons rainfall distribution restriction as well as high temperatures constitute a serious limitation for soil surface covering and crop production. For this reason it is very important to study alternatives for the no tillage system establishment in that State, specially for biomass production and for adequate management for better mulching in amount enough to improve soil physical quality and organic matter content. This study was carried out at the Lageado Experimental Station (UNESP - Botucatu, Brazil) from October 2001 through April 2004. The experiment consisted of a millet - soybean succession, under no-tillage, in which three millet sowing dates and five millet biomass management systems were tested. The aim was to evaluate alterations in some physical properties and in humic fractions of a Nitosol (Alfisol). The experiment was arranged in randomized blocks, in a split-plot scheme with four replications. The plots were represented by the sowing dates (S1, S2, S3) and the subplots as biomass harvest systems ( 1 (H1) - cut at each flowering and removal of biomass; 2 (H2) - cut at flowering and biomass maintenance; 3 (H3) - harvest only at first flowering and removal of biomass; H4 - harvest only at first flowering and biomass maintenance, and H5 - free growth, with no harvest. Undisturbed soil samples were collected from four layers (0-0.05, 0.05-0.10 and 0.10-0.20 m) to evaluate the physical properties. To quantify the humic fractions (C-HA, C-FA and C-HU), only the layers 0-0.05 and 0.05-0.10 m were analyzed. Pearl millet dry matter yield followed the order S1 > S2 > S3. Bulk density, macroporosity, microporosity and total porosity varied according to the millet sowing date. The continuous increment of biomass with a cut at each flowering and maintenance of the soil cover resulted in the greatest increase in the less stable OM fractions (humic and fulvic acids). To obtain a better soil cover, and improve soil physical quality (low bulk density, high total porosity) and higher soybean yield, millet sowing is recommended in the second and third date with harvest only after the first flowering, and always maintaining the millet residue on the soil surface.
bulk density; humic substances; no-tillage; Pennisetum glaucum; total porosity
