Managing soil organic carbon in tropical agroecosystems: evidence from four long-term experiments in Kenya

Summary

This long-term field study quantifies soil organic carbon dynamics across four Kenyan sites with contrasting climate and soil texture over 19 years of maize cultivation under varied organic and mineral inputs. Despite all treatments, SOC content declined substantially at all sites, though high-quality organic resources (Calliandra and Tithonia) applied at 4 t C ha⁻¹ yr⁻¹ limited losses to approximately 24% of initial SOC compared to 42% in unfertilised controls. The findings indicate that localised SOC recovery in intensively cultivated tropical agroecosystems requires sustained, substantial organic resource inputs, with resource quality and quantity interacting critically with site-specific soil properties.

Regional applicability

Whilst the study concerns tropical maize production in Kenya, the mechanistic findings on organic resource quality, application rates, and mineral nitrogen interactions may inform carbon-sequestration strategies in UK arable systems, particularly regarding the limits of organic matter inputs in counteracting baseline SOC decline in regularly cultivated soils. However, UK's cooler climate, different crop palette, and higher baseline soil fertility limit direct transferability.

Key measures

Soil organic carbon content and stocks (0–15 cm topsoil layer) measured repeatedly over 19 years; organic resource additions at 1.2 and 4 t C ha⁻¹ yr⁻¹; mineral nitrogen at 0 or 240 kg N ha⁻¹ yr⁻¹

Outcomes reported

The study measured changes in soil organic carbon (SOC) content and stocks over 19 years across four long-term field experiments in Kenya, assessing the effectiveness of different organic resource types and quantities combined with mineral nitrogen fertiliser in mitigating SOC decline in maize cropping systems.

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