Effects of Pinus caribaea forests on the C, N, P, and S status of Brazilian savanna Oxisols

The accumulation of humus in soils under Pinus caribaea Morelet forests may increase the availability of organically bound N, P. and S to plants and t hus improve soil fertility. To test this hypothesis, we compared C, N, P. a nd S concentrations and forms in soil solid phase and soil solution under P inus (PI) and natural savanna vegetation (Cerrado, CE). We sampled the 0-0. 15, 0.15-0.3, 0.3-0.8, 0.8-1.2, and 1.2-2 m soil depth layers of Oxisols fr om three spatially separated plots under CE and PI; at each plot, soil solu tion at 0.15, 0.3, 0.8, 1.2, and 2 m soil depth and under PI additionally b elow the organic layer was collected during two rainy seasons (21 October-2 8 April 1997/1998 and 1998/1999). Under PI, the organic layer stored more C (24.5 t ha(-1)), N (2.6 t ha(-1)) , P (140 kg ha(-1)), and S (261 kg ha(-1)) than under CE (1.2 t C ha(-1), 2 3 kg N ha(-1), 1.2 kg P ha(-1), 2.3 kg S ha(-1)). No significant difference in C, N, P, and S concentrations between CE and PI in the surface horizons of the mineral soil (C: 20.7-23.4 g kg(-1), N: 1.2-1.5 g kg(-1), P: 0.16-0 .26 g kg(-1), S: 0.18-0.21 g kg-l) was observed. However, at 1.2-2 m soil d epth C and organic N (N,,) concentrations were significantly higher under P I (C: 6.9 g kg(-1), N-org: 0.54 g kg(-1)) than under CE (C: 6.4 g kg(-1), N -org: 0.41 g kg(-1)). C/P and C/S ratios in soil solid phase decreased with increasing soil depth under CE and PI, those of C/N-org only under PI, lea ding to narrower C/N-org ratios under PI (12.9) than under CE (15.6) at 1.2 -2 m soil depth. The result indicated enhanced N transport to the subsoil u nder PI. Total organic C concentrations (TOC) in the soil solution were similar unde r CE and Pi and throughout the mineral soil. Under PI, TOC concentrations d ecreased sharply between the litter leachate (30 mg C l(-1)) and 0.15 m soi l depth (5 mg C l(-1)) indicating strong TOC sorption onto the surface mine ral soil. Total N concentrations in the soil solution were 11-23 times high er under PI than under CE. Organic N concentrations also decreased between the litter leachate and 0.15 m soil depth under PI but No, concentrations i ncreased from the litter leachate to 1.2 m soil depth and decreased between 1.2 and 2 soil depth, probably due to enhanced anion sorption at 2 m soil depth. No S and P was detectable in any solution sample. Higher C, N, and S storages and higher N availability under PI indicated that PI forests impr ove C, N, P, and S supply for plants in subsequent cultures and may therefo re be considered sustainable with respect to organically bound nutrients. ( C) 2001 Elsevier Science B.V. All rights reserved.