NATURAL ORGANIC MATTER: CHEMISTRY, FUNCTION AND FATE IN THE ENVIRONMENT Soil organic carbon as a key predictor of N in forest soils of Brazil Silas O. L. Calazans 1 & Vinicius A. Morais 2 & José R.S. Scolforo 2 & Yuri L. Zinn 1 & José M. Mello 2 & Luana T. Mancini 2 & Carlos A. Silva 1 Received: 16 March 2016 /Accepted: 8 September 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Purpose Despite the ancillary knowledge that soil N is chiefly retained as soil organic matter, little is known about how it is affected by other soil and environmental factors, especially in the tropics. In this study, we performed a comprehensive sur- vey of soils under native vegetation in Minas Gerais, Brazil, aiming to (a) measure soil Kjeldahl-N concentrations to a 1-m depth, (b) identify the main affecting factors of soil N reten- tion, and (c) predict N through soil profile based on organic C (SOC) and its main conditioning factors. Materials and methods Soils under 36 fragments of native forest and savanna were sampled at five depths (0–10, 10– 20, 20–40, 40–60, and 60–100 cm) and characterized by phys- ical and chemical analyses, including total N determined by the micro-Kjeldahl method. Single and multivariate regres- sions were used to predict N concentrations based on soil properties and climatic factors. Results and discussion The average N concentrations ranged between 0.12 and 7.54 g kg -1 , decreasing with depth, and can be predicted using SOC concentrations ( R 2 = 0.86). Multivariate regressions using more input data, namely tex- ture, cation exchange capacity (CEC), and altitude increased slightly R 2 values (0.68–0.90) for separate soil depths, but not for the whole dataset (R 2 = 0.85). Conclusions We demonstrated that N can be adequately pre- dicted based on SOC concentrations, for any depth and forest type. The implications of the stable SOC/N relation and their coupled cycles and the environmental factors affecting N re- tention in Brazilian weathered soils are further discussed. Keywords C and N soil cycles . Cerrado . Soil texture . Pedotransfer functions . Tropical forest . Weathered Brazilian soils 1 Introduction Nitrogen (N) is a major factor limiting biological production and a component of substances with potential deleterious en- vironmental impacts, such as NO 3 - leaching and N 2 O emis- sions. In soils, most N is intimately associated with soil organ- ic matter (SOM), and thus Jenny (1941) used N concentrations as an indicator of SOM concentrations in his seminal work. It is known that SOM and soil organic carbon (SOC) concentra- tions are controlled by external factors such as soil texture, relief, climate, and vegetation (Jenny 1941; Stevenson 1994; Quideau et al. 2001), among others. Thus, in soils under native vegetation, predicting SOC concentrations is difficult since each of those factors can be subdivided into sub-factors and all interact simultaneously in a complex network of infinite combinations. In consequence, there is high site specificity and wide variability in SOC, and, thus, in N concentrations among soil types, biomes, climatic zones, forest types, and also through the soil profile (Silva et al. 2004; Rangel et al. 2008; Cardoso et al. 2010; Cameron et al. 2013). Climate and vegetation significantly affect soil SOC and N concentrations by determining the balance between organic C inputs derived from plant production and C losses through microbial decomposition (Post et al. 1985; Brady and Weil Responsible editor: Heike Knicker * Carlos A. Silva csilva@dcs.ufla.br 1 Department of Soil Science, Federal University of Lavras, Lavras, MG 37200-000, Brazil 2 Department of Forestry, Federal University of Lavras, Larvas, MG 37200-000, Brazil J Soils Sediments DOI 10.1007/s11368-016-1557-4