Labile N and the nitrogen management index of oxisols in the Brazilian cerrados

Westerhof, Roelof; Vilela, Lourival; Ayarza, Miguel Angel; Zech, Wolfgang. 1999. Labile N and the nitrogen management index of oxisols in the Brazilian cerrados. In: Thomas, Richard J.; Ayarza, Miguel Angel (eds.). Sustainable land management for the oxisols of the Latin American savannas: Dynamics of soil organic matter and indicators of soil quality. Centro Internacional de Agricultura Tropical (CIAT), Cali, CO. p. 133-140. (CIAT publication no. 312)

The effect of land use on the availability of soil nitrogen (N) was studied by separating total soil N into one labile and one stable fraction by oxidation and extraction of labile N with potassium permanganate. The nitrogen management index (NMI) was calculated according to Blair et al. (1995) for the carbon management index. In all systems, labile N released by potassium permanganate was a better indicator for nitrogen availability than were total and stable N. The NMI was a good indicator for N availability but gave no information on 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 nitrogen 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, total N contents decreased, compared with native savanna. The availability of N under legume-based pastures and legume-based pasture/crop rotations was higher than under native savanna and continuous cropping systems.