Controlled Grazing of Maize Residues Increased Carbon Sequestration in No-Tillage System: A Case of a Smallholder Farm in South Africa

Khatab Abdalla,Macdex Mutema,Pauline Chivenge,Vincent Chaplot

doi:10.3390/agronomy11071421

Abstract

Despite the positive impact of no-tillage (NT) on soil organic carbon (SOC), its potential to reduce soil CO2 emission still needs enhancing for climate change mitigation. Combining NT with controlled-grazing of crop residues is known to increase nutrient cycling; however, the impacts on soil CO2 effluxes require further exploration. This study compared soil CO2 effluxes and SOC stocks from conventional tillage with free grazing (CTFG), NT with free grazing (NTFG), NT without grazing (NTNG), NT without crop residues (NTNR) and NT with controlled-grazing (NTCG), in South Africa. Soil CO2 effluxes were measured 1512 times over two years using LI-COR 6400XT, once to thrice a month. Baseline SOCs data were compared against values obtained at the end of the trial. Overall, NTCG decreased soil CO2 fluxes by 55 and 29% compared to CTFG and NTNR, respectively. NTCG increased SOCs by 3.5-fold compared to NTFG, the other treatments resulted in SOC depletion. The increase in SOCs under NTCG was attributed to high C input and also low soil temperature, which reduce the SOC mineralization rate. Combining NT with postharvest controlled-grazing showed high potential to increase SOCs, which would help to mitigate climate change. However, it was associated with topsoil compaction. Therefore, long-term assessment under different environmental, crop, and soil conditions is still required.

Highlights

Increased greenhouse gases (GHGs) concentrations in the atmosphere have contributed to the dramatic increase in global surface temperature since the late nineteenth century [1]
The current study showed no significant change of topsoil soil organic carbon (SOC) in the NT without grazing (NTNG) system, which agreed with several other studies [13,68,69], suggesting that crop residue retention alone might have little to no positive impact on SOCs in the short term
The main aim was to compare soil CO2 effluxes and SOC stocks among different tillage types combined with different maize residue management practices

Summary

Introduction

Increased greenhouse gases (GHGs) concentrations in the atmosphere have contributed to the dramatic increase in global surface temperature (by 0.8–1.5 ◦C) since the late nineteenth century [1]. Carbon dioxide (CO2) is one of the major GHGs in the atmosphere. The atmospheric CO2 accumulated to 545 ± 55 Pg C (1 Pg = 1015 g = 1 billion tonnes) over the years from 1870 to 2014 [2]. This quantity is in the same order of magnitude as the amount of carbon (C) in the biosphere (620 Pg C) and the atmosphere (720 Pg C). The rest is linked to agricultural malpractices such as deforestation, improper land use and land mismanagement, which lead to low soil C input from litter and high soil C losses, i.e., mineralization and soil erosion [3,4,5]

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Discussion

Conclusion