Resumen

YAGI, Renato et al. Soil organic matter as a function of nitrogen fertilization in crop successions. Sci. agric. (Piracicaba, Braz.) [online]. 2005, vol.62, n.4, pp. 374-380. ISSN 0103-9016.  http://dx.doi.org/10.1590/S0103-90162005000400011.

The interdependence between the C and N cycles is reflected by the levels of soil organic matter (SOM). SOM and organic C levels in water soluble (C-WS) humic acids (C-HA), fulvic acids (C-FA), and humin fractions (C-H) were evaluated through the classic chemical fractionation method in samples of a Rhodic Eutrudox from a randomized blocks experimental design, with split-split-plots using five nitrogen sidedressing levels for corn (0; 60; 120; 180; and 240 kg ha^-1 N) as the main treatment, two crop sequences (corn-corn and soybean-corn) as the secondary treatment, and two sampling depths (0 to 0.2 and 0.2 to 0.4 m) as a sub-subtreatment. Nitrogen fertilization did not affect SOM levels, but favored the synthesis of substances in the C-HA fraction. There was a quadratic effect of N rates on the C-WS and C-FA levels in the corn-corn succession. The soybean-corn succession resulted in larger SOM and organic C levels in the C-H fraction.

Palabras llave : humic acids; humin; urea; corn; soybean.