CARBON AND NITROGEN STOCKS IN THE ALFISOL SUBMITTED TO THE Eucalyptus urograndis MONOCULTURE AND Acacia mangium ROTATION

A busca de sistemas sustent\ue1veis de manejo do solo tem levado pesquisadores a desenvolverem novas t\ue9cnicas de cultivo. Dentre elas, destacam-se no Brasil estudos realizados com esp\ue9cies florestais capazes de fixar N2 atmosf\ue9rico e aumentar o estoque de C e N em fra\ue7\uf5es l\ue1beis e est\ue1veis da mat\ue9ria org\ue2nica do solo (MOS). O presente estudo teve por objetivo avaliar as altera\ue7\uf5es nos estoques de C e N em fra\ue7\uf5es das subst\ue2ncias h\ufamicas, da fra\ue7\ue3o leve da MOS e da mat\ue9ria microbiana em solos cultivados com Eucalyptus urograndis em rota\ue7\ue3o curta, eucalipto em rota\ue7\ue3o longa e povoamentos de Acacia mangium que sucederam plantios de eucalipto em rota\ue7\ue3o curta, tendo como refer\ueancia o solo de floresta nativa (Mata Atl\ue2ntica) adjacente. Foram quantificados os estoques de C org\ue2nico total e N total (COT e NT), nas fra\ue7\uf5es das subst\ue2ncias h\ufamicas (fra\ue7\ue3o \ue1cido f\ufalvico-AF, fra\ue7\ue3o \ue1cido h\ufamico-AH e fra\ue7\ue3o humina-H), C e N da fra\ue7\ue3o leve da MOS (C-MOL e N-MOL) e estoque de C e N da mat\ue9ria microbiana (C-BM e N-BM). Os resultados indicaram que o cultivo do eucalipto em rota\ue7\ue3o curta apresentou menores estoques de COT e NT, nas fra\ue7\uf5es das subst\ue2ncias h\ufamicas e, de N na mat\ue9ria microbiana em compara\ue7\ue3o ao solo sob rota\ue7\ue3o com Acacia mangium. O cultivo de Acacia mangium e o aumento do tempo da rota\ue7\ue3o do eucalipto incrementaram os estoques de C e N da maioria das fra\ue7\uf5es l\ue1beis (C-MOL, N-MOL e C-BM) e est\ue1veis (C e N nas subst\ue2ncias h\ufamicas), indicando tend\ueancia de recupera\ue7\ue3o dos seus estoques para valores pr\uf3ximos daqueles originais (mata nativa), sendo superiores aos estoques obtidos na \ue1rea de eucalipto em rota\ue7\ue3o curta.The pursuit of sustainable systems of soil management has led researchers to develop new techniques of cultivation. Among them, studies with forest species able to fix atmospheric N2 and increase C and N stocks in labile and stable soil organic matter (SOM) stand out in Brazil. The study aimed to evaluate changes in stocks of C and N in fractions of humic substances, light fraction of SOM and microbial biomass in soils of short-rotation Eucalyptus \u201curograndis\u201d, long rotation plantations and stands of Acacia mangium which succeeded short rotation eucalyptus monoculture, in comparison to the soil of native forest (Atlantic Forest). It was obtained the total organic carbon (TOC) and total nitrogen (TN) stocks, C and N stocks in the fractions of humic substances (fulvic acid fraction-AF, humic acid fraction-HA and humin fraction-H), C and N in light fraction of SOM (C-LOM and N-LOM) and C and N microbial biomass (CMB and N-MB). The results indicated that the short rotation eucalyptus cultivation reduced total organic carbon stocks, total nitrogen, C and N in the humic substances, and N storage in the microbial biomass compared to Acacia mangium soil. The cultivation of Acacia mangium and the increase of the eucalyptus rotation time increased stocks of C and N of the labile (C-LOM, N-LOM and C-MB) and stable fractions (C and N in humic substances) indicating a significant recovery of their stocks to levels approaching those original (native), and higher than stocks obtained in the soil of short rotation eucalypt