A study published in the International Journal of Agriculture and Environmental Research by O. Saidy, D. K. Isutsa, and colleagues assessed the economic and agronomic potential of various organic fertilizers in enhancing Iceberg lettuce (Lactuca sativa L.) production. The research compared six treatments—negative control, positive control (NPK + Urea), charged biochar, compost, poultry manure, and farmyard manure—over two distinct seasons in Kenya. The overall goal was to assess sustainable practices against synthetic fertilizers in tropical regions. The core economic finding focused on the Net Economic Benefit (NEB), which showed highly significant differences among treatments in both seasons (P=0.001 and P=0.011). While the positive control (NPK + Urea) yielded the highest NEB in Season 1 (Ksh 778 per 3 m2 plot) , poultry manure delivered the greatest profit in Season 2, generating Ksh 833 per 3 m2 plot. This outperformance in the second season suggests that the cumulative benefits of nutrient mineralization from the organic source promoted high yields that generated a higher net return than the high-cost synthetic fertilizers.

In contrast, the charged biochar treatment consistently recorded the lowest short-term profit among the organic amendments (Ksh 217 in Season 1 and Ksh 298 in Season 2). This low short-term profitability is mainly attributed to the high initial input cost of biochar and its characteristic slow nutrient release, which masks its long-term soil health benefits. Beyond profitability, the organic amendments significantly improved soil properties. Poultry manure emerged as the most nutrient-dense organic material, before application, exhibiting the highest organic matter (27.03%), phosphorus (994.8 ppm), and CEC (69.43 meq/100g) content, thus facilitating rapid mineralization and nutrient release. However, the charged biochar showed significant long-term benefits by enhancing soil Cation Exchange Capacity (CEC), with the biochar-treated bed showing the highest post-production CEC (24 meq/100g) in one season. More notably, biochar-treated plots maintained the highest phosphorus concentration compared to poultry manure in the final soil analysis of both seasons. This indicates biochar’s strong ability to absorb, retain, and reduce phosphorus leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More losses.

In terms of crop quality, the organic fertilizers significantly enhanced vitamin C content more than no fertilizers (P=0.001 and P=0.048). Poultry manure produced the highest vitamin C concentration in Season 1 at 3.2 mg/100 g. There were, however, no statistically significant differences found among any treatments for the mineral nutrients (N, P, K, Mg, and Ca) in the lettuce leaf tissue.

The study concluded that poultry manure should be promoted as the primary, most profitable organic amendment in tropical lettuce production. Despite the lower short-term profits, biochar warrants further research into its long-term residual effects due to its noted ability to sustain CEC and phosphorus retention.

Source: Saidy, O., Isutsa, D. K., & Karanja, B. K. (2025). Assessment of charged biochar and selected organic fertilisers effects on soil properties, nutritional quality, and profitability of lettuce. International Journal of Agriculture and Environmental Research, 11(4)