Carbon Manageme...

By Rita Juma

INTRODUCTION

Climate change remains one of the most significant global environmental challenges, largely driven by increased concentrations of greenhouse gases, particularly carbon dioxide (CO₂), in the atmosphere. Agricultural systems play a dual role in climate change as both sources and sinks of carbon. Properly managed agricultural lands have the potential to sequester substantial amounts of carbon, thereby mitigating climate change.

Sugarcane is a major commercial crop grown extensively in tropical and subtropical regions and contributes significantly to agricultural economies. In many sugarcane-growing areas, intensive cultivation practices such as frequent tillage, residue burning, and excessive fertilizer use can lead to soil organic carbon depletion. Conversely, improved management practices such as residue retention, reduced tillage, and integrated nutrient management can enhance soil carbon storage.

Assessing carbon stocks in sugarcane-growing soils and associated biomass is essential for understanding the role of these systems in carbon sequestration. The Carbon Management Index (CMI) is a useful indicator that integrates both the quantity and quality of soil organic carbon and reflects the impact of land management practices on soil health. However, limited localized data exist on carbon stocks and CMI in sugarcane production systems, particularly under different management regimes.

Carbon Management index definition: is an assessment model that shows how a particular land use affects the soil quality relative to reference land use soil. It evaluates the effectiveness of conservation management systems in maintaining soil organic matter and mitigation of greenhouse gas emissions. The index formula entails the carbon pool index and the Lability index of the soil under a particular land use. Soil organic carbon has been linked to its potential role in carbon sequestration through proper management of land use and types.

• Carbon stock index(CSI)- Measures total organic carbon stock in the soil.
• Carbon Management Index(CMI) – Evaluates the overall impact of management practices on soil health.
• Soil Organic Carbon (SOC): This is the largest pool, with stock changes often measured in the top 0–30 cm or 0–100 cm layers.
• Above-ground Biomass: Includes stalks and leaves, with studies indicating leaves can store approximately 877 kg ha⁻¹ and stalks 362 kg ha⁻¹ of carbon.
• Below-ground Biomass: Roots contribute significantly to carbon storage, with estimations showing around 621 kg ha⁻¹. 

 

 

 

Problem definition: Effects of Land use cover on Soil Organic Carbon

The changes in land use cover have a strong effect on total soil organic carbon, its fractions and its overall soil health; Increasing anthropogenic disturbances especially, on land use/cover change, is a major cause of soil quality deterioration in the world as a whole; soil organic carbon has recently gained prominence in assessment of soil quality since it compoundly affects the chemical, physical and biological aspects of the soil. Despite the extensive cultivation of sugarcane, there is insufficient empirical data on soil and biomass carbon stocks and the Carbon Management Index in sugarcane-growing areas.

Soil Organic Carbon (SOC) and its fractions serve as critical, sensitive indicators for evaluating the Carbon Management Index (CMI) to measure land-use impacts in Kenya and globally. CMI, which integrates total soil organic carbon (TOC) and carbon lability, acts as an early warning indicator for soil degradation or improvement caused by land use changes, such as converting forests to agricultural land or overgrazing in grasslands. 

 

Key Findings in Kenya

• Land Use Impact on CMI: Studies in Kenya (e.g., Narok County) show that land use types significantly affect CMI. Shrublands generally show higher Total Organic Carbon (TOC), Particulate Organic Carbon (POC), and Mineral Organic Carbon (MOC) compared to degraded grasslands and bare lands.
• Degradation Assessment: CMI has been effectively used to show that overgrazed grasslands in Kenya are often more degraded than agricultural lands, despite misconceptions that cultivation is always more damaging, due to the loss of labile carbon in the soil.
• Particulate Organic Carbon (POC): POC is identified as the most sensitive pool and a better early indicator for soil degradation compared to Total Organic Carbon (TOC).
• Dryland Vulnerability: With 80% of Kenya classified as drylands, land-use changes—such as conversion for agriculture and deforestation—severely deplete organic carbon, leading to nutrient deficiencies in 75% of the soil.
• Sustainable Management: Implementing conservation agriculture and reducing grazing pressure are critical for increasing carbon sequestration in Kenyan soils. 

 

Global Context

• Soil as a Carbon Pool: Soils constitute the largest carbon sink in the terrestrial biosphere, acting as a crucial component in global carbon cycle monitoring.
• Land Use Change Impacts: Globally, land use conversion from natural ecosystems to agricultural or urban use results in significant carbon loss, with land-use changes responsible for an estimated 18% of global greenhouse gas emissions.

Key Indicators Used:

• Total Organic Carbon (TOC): Reflects total carbon stocks.
• Particulate Organic Carbon (POC): A highly sensitive indicator of early degradation.
• Mineral Organic Carbon (MOC): Stable, long-term carbon storage.
• Lability: The ratio of labile to non-labile carbon.
• C: N Ratio: Used to evaluate nutrient status. 

• Mono-cropping as an aspect land degradation

Carbon stocks in Kenyan sugar-growing regions, particularly in Western Kenya, are heavily influenced by continuous mono-cropping, which reduces Soil Organic Carbon (SOC) compared to agroforestry systems. Studies show significant SOC losses due to tillage, with better sequestration potentials when incorporating agroforestry or improved residue management. Globally, sugarcane provides moderate carbon storage, often increased by lower straw removal (<34%) and vinasse application, acting as a crucial, manageable carbon pool. 

 

Carbon Stocks in Kenyan Sugar Regions (Western Kenya)

• Land Use Impact: Sugarcane farming systems in Western Kenya often result in lower total soil organic carbon stocks (TSOCst) compared to alternative land-use systems like agroforestry.
• Soil Management: Continuous tillage (tractor vs. oxen) in sugar zones affects soil properties and lowers carbon levels.
• Agroforestry Benefits: Incorporating agroforestry, such as with Markhamia lutea or Leucaena leucocephala, increases SOC stock across different soil depths, acting as a potential climate mitigation strategy.
• Aboveground Carbon (AGC): While focusing on sugarcane, agroforestry systems with trees like Grevillea robusta in cropland (1220 m range) contribute significantly to aboveground biomass. 

 

Global Sugarcane Carbon Dynamics

• SOC Sequestration: Sugarcane cultivation can act as a carbon sink or source, with soil organic carbon accumulation in clayey soils at rates of roughly of straw.
• Straw Management: Maintaining moderate to low removal of sugarcane straw (<34%) holds carbon better than heavy removal (>66%), which leads to significant losses.
• Organic Amendments: Application of vinasse (a byproduct) has been shown to increase SOC stocks.
• Ecosystem Services: While sugarcane production can affect carbon storage, studies suggest it is often overlooked in traditional ecosystem service evaluations. 

 

Key Findings on Carbon Assessment

 Assessments in Kenya combine field inventory, allometric equations (e.g. For trees), and remote sensing for both above- and belowground carbon. In addition to agricultural land, Western Kenya’s carbon sequestration studies often include assessments in protected areas like the Kakamega and North Nandi forests, which show higher carbon storage, particularly in undisturbed areas. The same can be applied to sugar growing zones within the country.

For a broader perspective on Kenya's total biomass potential, the Preliminary Assessment of Carbon Storage & the Potential for Forestry-Based Carbon Offset report, citing Brown & Gaston (1995), notes that Kenya has the potential to double its current aboveground biomass. 

In South-Central Brazil, a major production hub, converting pasture to sugarcane has a generally neutral to positive effect on SOC, while converting native vegetation causes significant carbon losses. Sustainable management practices, such as unburnt harvesting (trash retention), reduced tillage, and vinasse application, are key to enhancing carbon sequestration, with some systems showing a 10% to 24% increase in SOC stocks. 

Impacts of Land Use Changes (LUC)include in sugarcane growing areas include;

• Pasture to Sugarcane: This Often has a neutral effect or increases SOC when replacing degraded pasture.
• Native Vegetation to Sugarcane: This Leads to a reduction in SOC stocks, with losses of 0.8% to 3.3% in the first 20 years.
• Annual Crops to Sugarcane: Initial losses (approx. 1.6% in 0–10 years) can be reversed after 20 years. 

Management Practices Affecting Carbon Stocks in Sugar zones

• Trash Management (Unburnt Harvesting): Replacing pre-harvest burning with unburnt harvesting (green cane) increases SOC stocks by 1.5 Mg ha⁻¹ year⁻¹ (surface to 30 cm).
• Straw Removal: High removal rates (>66%) for bioenergy can reduce SOC stocks by up to 9.9%, whereas low removal (<34%) is relatively neutral.
• Vinasse Application: Applying this liquid byproduct increases SOC stocks by up to 10%.
• Reduced Tillage: Reduces soil disturbance, leading to up to 24% higher SOC stocks in topsoil compared to conventional tillage. 

 

 

 

 

CONCLUSION

 

The use of CMI and SOC allows for the identification of sustainable land management practices, which is crucial for increasing soil productivity and mitigating climate change in Sugarcane growing areas in Kenya. Continuous mono cropping, residue burning, and intensive soil disturbance may be degrading soil carbon pools, yet these effects are rarely quantified. Without reliable data on carbon stocks and CMI, it is difficult to design or recommend sustainable sugarcane management practices that enhance carbon sequestration and soil health. This knowledge gap limits informed decision-making for climate-smart agriculture and sustainable land management. Existing research often focuses on soil nutrients and yield; carbon dynamics and management indices are understudied in Kenyan sugar belts.

CMI for Sustainability: The CMI is used worldwide to assess the capacity of a land management practice to maintain or improve soil quality by monitoring the balance between total carbon and active (labile) carbon pools. I strongly recommend more research to be done and appreciate the significance of Carbon Management Index as a key component in assessment of land use practices in Sugarcane growing zone in Kenya to aid in protection of soil, especially by implementing key factors that reduce soil nutrient degradation.