Land use effects on labile N extracted with permanganate and the nitrogen management index in the Cerrado region of Brazil

Abstract

The effect of land use on the availability of nitrogen (N) was studied by separating total N into a labile and a stable fraction by oxidation and extraction of labile N with KMnO4. The nitrogen management index (NMI) was calculated following the method of Blair et al. (1995) for the carbon management index. In all systems, labile N released by KMnO4 was a better indicator of N availability than total and stable N. The NMI was a good indicator of N availability but gave no information about the total amount of N. In land use system analysis, total N and labile N can be used together as a simple and rapid way to evaluate the N status of the soil. Legume-based pastures specifically increased the amount of labile N. Although soybeans had a dominant role in the continuous cropping systems studied, the total N contents of these systems were lower than those of the natural Cerrado. The availability of N under legume-based pastures and legume-based pasture-crop rotations was higher than under the natural Cerrado and the continuous cropping systems