Composition of organic matter in a subtropical Acrisol as influenced by land use, cropping and N fertilization, assessed by CPMAS ¹³C NMR spectroscopy

Abstract

We know much about the influence of management on stocks of organic matter in subtropical soils, yet little about the influence on the chemical composition. We therefore studied by CPMAS 13 C NMR spectroscopy the composition of the above-ground plant tissue, of the organic matter of the whole soil and of silt-and clay-size fractions of the topsoil and subsoil of a subtropical Acrisol under grass and arable crops. Soil samples were collected from three no-till cropping systems (bare soil; oatsÀmaize; pigeon pea þ maize), each receiving 0 and 180 kg N ha À1 year À1 , in a long-term field experiment. Soil under the original native grass was also sampled. The kind of arable crops and grass affected the composition of the particulate organic matter. There were no differences in the composition of the organic matter in silt-and clay-size fractions, or of the whole soil, among the arable systems. Changes were observed between land use: the soil of the grassland had larger alkyl and smaller aromatic C contents than did the arable soil. The small size fractions contain microbial products, and we think that the compositional difference in silt-and clay-size fractions between grassland and the arable land was induced by changes in the soil's microbial community and therefore in the quality of its biochemical products. The application of N did not affect the composition of the above-ground plant tissue nor of the particulate organic matter and silt-size fractions, but it did increase the alkyl C content in the clay-size fraction. In the subsoil, the silt-size fraction of all treatments contained large contents of aromatic C. Microscopic investigation confirmed that this derived from particles of charred material. The composition of organic matter in this soil is affected by land use, but not by variations in the arable crops grown.

Compartimentos de carbono orgânico em Latossolo cultivado com hortaliças sob diferentes manejos

“…Esses resultados estão ligados à forma de distribuição da palhada no perfil do solo, nos diferentes sistemas. No SPD, a palhada é mantida em superfície; no PPR, é incorporada com grade semiaberta regulada para distribuí-la à profundidade aproximada de 0,10 m; e, no SPC, ela é incorporada em profundidade pelas operações de aração e gradagem, normalmente efetuadas para atingir profundidade em torno de 0,20 m. A importância da forma do aporte da biomassa de plantas de cobertura ao solo, para o acréscimo da fração particulada da matéria orgânica, já foi relatada anteriormente (Dieckow et al, 2005;Sá & Lal, 2009;Salvo et al, 2010;Briedis et al, 2012). Os teores de COAM, em geral, apresentaram comportamento inverso aos de COP (Tabela 4).…”

Changes in soil organic matter composition are associated with forest encroachment into grassland with long‐term fire history

“…In the surface horizons of the C 4 grassland soils (G, GS), the C distribution among spectral regions of 13 C NMR spectroscopy in the heavy organo-mineral fraction was similar compared with those from Ferralsols (Dalmolin et al, 2006) and Acrisols (Dieckow et al, 2005) with native subtropical grassland in southern Brazil. However, they differed with soil depth, with a strong increase of aromatic C, which is associated with decreasing O-alkyl and alkyl C contents; carboxyl C had irregular trends (Table 1).…”

“…There has been no input of charred organic material into the grassland soils for 15 years because burning ceased in the Pro´-Mata reserve. The predominant presence of charred material in subsoils as a result of bioturbation was detected in several studies (Glaser et al, 2000;Dieckow et al, 2005). The charred material may also have been lost through the complete oxidation by subsequent fires (Ohlson & Tryterud, 2000;Czimczik et al, 2005;Knicker et al, 2006).…”

Characterization of cover crops by NMR spectroscopy: impacts on soil carbon, nitrogen and phosphorus under tillage regimes

“…Soil management systems such as the use of notillage techniques and rotation with cover crops have also an effect on the accumulation of C, N and P in the soil (DIECKOW et al, 2005a;GRANDY et al, 2008;METAY et al, 2007;SÁ et al, 2014;TIVET et al, 2013). Considering 31,5 million hectares under no-tillage in Brazil in (FEBRAPDP, 2012 and that an increase of 8 million hectares by 2020 has been planned by the Brazilian government as one of the main approaches for greenhouse gas mitigation (BRASIL, 2012), more information is needed on the chemical composition of decomposing plant residues and their influence on the stocks of carbon and other nutrients.…”