Soil Organic Carbon and Labile Carbon Pools Attributed by Tillage, Crop Residue and Crop Rotation Management in Sweet Sorghum Cropping System

Mashapa Elvis Malobane,Adornis Dakarai Nciizah,Isaiah Iguna Chabaari Wakindiki,Fhatuwani Nixwell Mudau

doi:10.3390/su12229782

Abstract

Labile organic carbon (LOC) fractions are considered as sensitive indicators of change in soil quality and can serve as proxies for soil organic carbon (SOC). Although the impact of tillage, crop rotation and crop residue management on soil quality is well known, less is known about LOC and SOC dynamics in the sweet sorghum production systems in South Africa. This short-term study tested two tillage levels: no-till and conventional-tillage, two crop rotations: sweet-sorghum/winter grazing vetch/sweet sorghum and sweet-sorghum/winter fallow/sweet sorghum rotations and three crop residue retention levels: 30%, 15% and 0%. Tillage was the main factor to influence SOC and LOC fractions under the sweet sorghum cropping system in South Africa. NT increased SOC and all LOC fractions compared to CT, which concurs with previous findings. Cold water extractable organic carbon (CWEOC) and hot water extractable organic carbon (HWEOC) were found to be more sensitive to tillage and strongly positively correlated to SOC. An increase in residue retention led to an increase in microbial biomass carbon (MBC). This study concludes that CWEOC and HWEOC can serve as sensitive early indicators of change in soil quality and are an ideal proxy for SOC in the sweet-sorghum cropping system in South Africa.

Highlights

The potential use of bioenergy sweet sorghum in South Africa, like in other countries, offers an opportunity for valuable use of marginal land and income to smallholder farmers at low agronomic inputs [1]
No significant interaction among the three factors was found on Soil organic carbon (SOC), Cold water extractable organic carbon (CWEOC), hot water extractable organic carbon (HWEOC) and Particulate organic matter (POM), while microbial biomass carbon (MBC) was influenced (p < 0.05) by tillage × rotation × residue management interaction (Table 1)
MBC, CWEOC, HWEOC and POM, which form part of Labile organic carbon (LOC), were 9.58%, 70.89%, 35.42% and 18.30% higher in NT compared to CT treatment, respectively

Summary

Introduction

The potential use of bioenergy sweet sorghum in South Africa, like in other countries, offers an opportunity for valuable use of marginal land and income to smallholder farmers at low agronomic inputs [1]. Biofuel feedstock production is generally done under intensive agronomic management [2], which has potential to reduce soil quality [3] and intensify soil erosion and its related consequences [4]. Conserving and restoring soils in marginal lands is at the centre of sustainable production of bioenergy crops, and it will serve as a poverty alleviation strategy [5]. To date, sustainable production systems for bioenergy sweet sorghum in South Africa are not available [7]. Research on the effect of CA on soil quality under the production of biofuel feedstock is required in South Africa [2]. The potential benefits of CA under sweet-sorghum production systems for vital soil health indicators such as LOCs were not examined in depth

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Conclusion