Impact of Soil Organic Carbon Dynamics on Vegetable Productivity in Intensively Farmed Systems of South East Nigeria

Intensive vegetable production in the densely farmed smallholder landscapes of South East Nigeria is accelerating the depletion of soil organic carbon, undermining the long-term productive capacity of horticultural soils. Understanding the dynamics of organic carbon under different management regimes is essential for designing sustainable soil health interventions tailored to the region's production systems. This study investigates the relationship between soil organic carbon dynamics and vegetable productivity under five soil management systems, including no amendment, poultry manure alone, biochar alone, NPK alone, and combined poultry manure and biochar, in intensively cropped vegetable fields in Enugu and Imo states over two cropping seasons. Soil organic carbon, microbial biomass carbon, bulk density, and available nutrient levels were monitored at planting and post-harvest. Vegetable yield data for tomato and leafy amaranth were correlated with soil carbon metrics using structural equation modeling. Results indicate that combined poultry manure and biochar application produced the most significant improvement in soil organic carbon and maintained the highest vegetable yields across both seasons. The study provides evidence for a positive feedback loop between soil carbon enrichment and horticultural productivity in South East Nigeria. Keywords: soil organic carbon, vegetable productivity, biochar, South East Nigeria, soil health