Land use, tillage, texture and organic matter stock and composition in tropical and subtropical Brazilian soils

Abstract

We examined the influence of land use change, tillage system and soil texture on organic carbon (C) stocks and on organic matter composition of tropical and subtropical soils from Brazil at four long-term experiments (11-25 years) based on fine-and coarse-textured soils. Soil samples were collected from the 0-5, 5-10 and 10-20 cm layers of conventional tillage (CT) and no-till (NT) plots, and of the adjoining soil under native vegetation (NV) of Cerrado (tropical) or grassland (subtropical). Conversion of NV to CT resulted in losses of 7-29% of the original C stock of 0-20 cm; conversion to NT increased this C stock by 0-12% compared with CT. Organic matter composition of the 0-5 cm layer, assessed by solid state CPMAS-13 C-NMR, ESR and laser induced fluorescence spectroscopies, was affected by land use and tillage systems. Conversion of NV to CT decreased O-alkyl and increased aromatic, carbonyl, aromatic/O-alkyl ratio, free radicals concentration and fluorescence signal. The opposite trend was observed when NT replaced CT. The relative losses and gains of C and qualitative changes resulting from land use and tillage were less evident in fine-than in coarse-textured soils, suggesting a greater resistance and a smaller resilience of fine-compared with coarse-textured soils. The direct relation between increase in C stock and increase in potentially labile moieties (e.g. O-alkyl) and the decrease in more recalcitrant moieties (e.g. aromatics) in NT soils suggests that spatial inaccessibility by aggregates is playing a major role, compared with selective preservation, in promoting C accumulation in NT soils.

Tillage impacts on the fractions and compositions of soil organic carbon

“…Some reports found obvious changes in the composition of soil organic matter after shifting from no tillage to plowing tillage (e.g. Dieckow et al, 2009), furthermore, the study of Solomon et al (2007) highlighted the decline of O-alkyl C, acetal-C and aliphatic C after a long-term of anthropogenic perturbations for tropical forest and sub-tropical grassland ecosystems. Parton et al (1987) divided SOC into three fractions, including active SOC [the mean residence time (MRT) is about 1-5 years cycle], slow SOC (MRT is about 20-40 years), and passive SOC (MRT is about 200-1500 years).…”

A review on soil carbon accumulation due to the management change of major Brazilian agricultural activities

“…This indicates that differences in soil texture did not result in significant differences in soil carbon sequestration, as similar accumulation rates were observed when more conservationist practices were implemented. In general, the primary factors contributing to the accumulation of C in the soil of annual crops are no-till practices and crop rotation sequences using leguminous plants, which remove atmospheric nitrogen via a symbiotic interaction, leaving large amounts of dry matter on the soil surface (Dieckow et al, 2005).…”

“…It is imperative to consider the reform of sugarcane fields in those studies, as well as the contribution of emissions due to other mechanised operations in those areas. Other aspects of the stability of labile carbon, already investigated in southern Brazil (Dieckow et al, 2009), should also be incorporated in forthcoming studies with the aim of a better understanding of the possible causes and effects related to soil carbon sequestration in sugarcane areas. New strategies that would result in reduced frequency and intensity of soil tillage would be welcome, especially in sugarcane areas where the so-called no-till practice is not used, differently from annual cultures.…”

“…It is noteworthy that the deviation of the C accumulation rate is small along the years of conversion to no-till, though some works have shown, for example, a depletion in soil C after 17 years of conversion. Many of the studies conducted in annual crops indicated a strong causeand-effect relationship between C sequestration potential and soil tillage practices, as well as the amount of crop residue input on the soil, especially in strategies combining crop rotation with no-till practices (Dieckow et al, 2009). …”

Changes in Soil Organic Carbon and Nitrogen Stocks in Long-Term Experiments in Southern Brazil Simulated with Century 4.5

“…Conversely, no-tillage (NT), combined with large crop residues left on soil, has been shown to be an effective agricultural practice for C sequestration and mitigation of GHG emissions (West and Post, 2002;Carvalho et al, 2009). However, in addition to management practices, SOM dynamics are markedly dependent on site-specific factors such as soil type, climate, and antecedent (original) stocks (Zinn et al, 2005a;Dieckow et al, 2009). …”