Recalcitrant carbon and nitrogen in agriculture soils with residue accumulation and fertilization under tropical conditions

  • Joseph Elias Rodrigues Mikhael Louisiana State University, College of Agriculture
  • Risely Ferraz Almeida Luiz de Queiroz College of Agriculture, University of São Paulo
  • Fernando de Oliveira Franco
  • Roberta Oliveira Camargo
  • Beno Wendling Federal University of Uberlândia, Institute of Agricultural Sciences
Keywords: brachiaria pasture, humin, fulvic acid, humic acid, organic matter


Soil organic matter has a strong relation to total organic carbon, and about 85% of organic carbon consists of humic substances (HS), classified as humin (HU), humic (HA) and fulvic acids (FA), and denominated as recalcitrant carbon in soil. HS are formed by complex, heterogeneous and polydisperse molecules, which have significant influence on the soil physical and chemical characteristics. The study evaluates the hypothesis that agricultural soils treated with organic residues may present higher carbon stocks as presented in forest soils.  The aim of this study was to evaluate alterations in recalcitrant carbon and nitrogen stocks in Oxisol (Forest - FL, unfertilized Brachiaria - UB, and fertilized Brachiaria - FB) and Cambisol (Forest - FC, Coastcross - CC, sugarcane - CA, and silage corn - SM) at surface (0.0 - 0.1) and subsurface (0.1 - 0.2 m), in the Zona da Mata in Minas Gerais state, Brazil. Result shows that fertilization, low soil disturbance and residual removal promoted increase of C and N content in HS, being close to native forests. Both, carbon and nitrogen recalcitrant, presented reduction with soil depth. HU ranged from 10.5 to 16.7 g kg-1 and presented the highest concentration compared to FA and HA. In Oxisol, FL and FB presented the highest SH concentration and demonstrate the positive effect of fertilization on carbon stocks improving soil quality in well-managed and productive areas. While, In Cambisol, FC and CC presented higher carbon and nitrogen in HS, mainly for HU and HA fractions, and SM showed the lowest concentrations in all fractions. Our results suggest that soil managements with lower soil disturbance and residual removal promotes increasing of carbon and nitrogen in recalcitrant fraction, with concentration close to native forests. Pasture should be fertilized to improve recalcitrant carbon and nitrogen stocks, avoiding process of degradation in tropical soil. It is an important outcome due to high levels of degraded areas in Brazil caused by inadequate use of soil mainly with pasture.


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Author Biographies

Joseph Elias Rodrigues Mikhael, Louisiana State University, College of Agriculture
School of Plant, Environmental and Soil Sciences, 137 J.C. Miller Hall, Baton Rouge, LA 70803
Risely Ferraz Almeida, Luiz de Queiroz College of Agriculture, University of São Paulo

Department of Soil Science, Av. Padua Dias 11, Piracicaba, SP, Brazil, 13418-900

Beno Wendling, Federal University of Uberlândia, Institute of Agricultural Sciences
Department of Soil Science,Av. Amazonas, Campus Umuarama,  Bloco 4C, Uberlândia, MG, Brazil, 38400-734
Agricultural Sciences