Carbon indices to assess quality of management systems in a Subtropical Acrisol

Josiléia Acordi Zanatta,Frederico Costa Beber Vieira,Clever Briedis,Jeferson Dieckow,Cimélio Bayer

doi:10.1590/1678-992x-2017-0322

Abstract

ABSTRACT: Management systems to improve soil quality are essential for agricultural and environmental sustainability. We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF). In addition, we examined their relationship to chemical, physical and biological soil quality indicators, as well as to maize yield. The study was conducted on a long-term experiment (18 years) in southern Brazil involving two different systems [no tillage (NT) and conventional tillage (CT)], two cropping systems [black oat/maize (O/M) and black oat + vetch/maize + cowpea (OV/MC)] and two nitrogen fertilizer rates for maize (0 and 180 kg ha–1). Based on the three indices, the best managements for soil quality comprised NT (50-212 % better than CT), legume cover crops (10-47 % better than O/M) and N fertilization (8-33 % better than no fertilizer). All three indices proved accurate to assess the impact of soil management systems, especially SR-LF, which showed increased sensitivity and close relationships with chemical, physical and biological soil quality indicators. On the other hand, a poor relationship was observed between soil C indices and maize yield, which was improved only by legume cover crops and N fertilization. The results showed that the association of no-till system to an abundant supply of crop residues is key to ensure high soil quality and crop yields in humid subtropical regions.

Highlights

Conventional tillage (CT) has contributed to a faster decline of original soil carbon (C) stocks, thereby having an adverse impact on soil and environment quality mainly in tropical and subtropical regions (Houghton, 2014; Lal, 2004)
We assessed the quality of soil management systems applied to a subtropical Acrisol in terms of the carbon management index (CMI), the stratification ratio for total organic carbon (SR-TOC) and light fraction of organic matter (SR-LF)
The system based on legume cover crops (OV/MC) increased C pool index (CPI) by 17 % on average compared to the system based only on grass (O/M, Table 4)

Summary

Introduction

Conventional tillage (CT) has contributed to a faster decline of original soil carbon (C) stocks, thereby having an adverse impact on soil and environment quality mainly in tropical and subtropical regions (Houghton, 2014; Lal, 2004). The high soil degradation rates contrast with the target of agriculture to feed a population increase of 45 % until the end of the century (Gerland et al, 2014). Conservation management systems such as no-tillage (NT) promote soil C accumulation by keeping a less oxidative environment (Bayer et al, 2000; Sá et al, 2015; Tivet et al, 2013). The CMI index has successfully been used to assess soil quality in management systems in subtropical and tropical regions (Diekow et al, 2005; Souza et al, 2014). Several studies have reported a high SR with improvements in soil quality indicators under conservation management systems (Franzluebbers, 2002; Franzluebbers, 2010; Sá and Lal, 2009)

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Conclusion