Effects of charged biochar and selected organic fertilisers on growth, yield, quality, and profitability of lettuce (lactuca sativa l.)

Abstract

Poor soil fertility due to excessive use of synthetic fertilisers poses challenges to sustainable production of vegetables, including lettuce (Lactuca sativa L.) in many tropical regions. This research aimed at assessing the agronomic and economic potential of organic fertilisers in enhancing lettuce production. Its specific objectives were to determine the effects of selected organic fertilisers (nutrient source) on soil properties, productivity, quality, and profitability of lettuce. It was done in a randomized complete block design with six treatments (negative control- soil, positive control-NPK+Urea, charged biochar, compost, poultry and farmyard manures) replicated three times in two production seasons from October, 2024 to January, 2025, and February to May, 2025 in Field-3 at Egerton University, Kenya. Iceberg lettuce variety was used in this experimentation. Data was collected pre- and post-production on soil and organic fertilisers; bi-weekly on lettuce growth components; and in the 9"‘ week on head diameter, biomass yield, nutritional quality, and net economic benefit (NEB). Data was subjected to analysis of variance using JMP Pro 7‘h edition program. Results showed decreased N, P, pH, OC, OM, but increased K, Ca, Mg, CEC, and C: N in soil post-production. All treatments had a pH of 6.1 - 6.5 that was optimal for lettuce growth. In both seasons, results showed a significant difference in lettuce leaf diameter (P = 0.023, 0.041), plant height (P = 0.002, 0.004), leaves (P = 0.032, 0.0002), as well as head diameter (P = 0.012, 0.01 1). Similarly, marketable fresh weight yield was significantly (P = 0.010; 0.019) different and ranged from 1.4 - 2.6 ton/ha and 1.1 - 2.6 ton/ha. In this regard, poultry manure promoted the highest marketable fresh weight yield of 2.3 and 2.6 ton/ha. In contrast, charged biochar led to intermediate marketable fresh weight yield of 2.0 and 1.8 ton/ha, while negative control had the lowest of 1.4 and l.l ton/ha. Lettuce leaf tissue analysis showed significant (P = 0.001; P = 0.048) differences in vitamin C, ranging from 2.0 — 3.2 and 1.0 — 1.4 meg/100 mg. However, there were no significant (P> 0.05) differences in nutritional minerals (N, P, K, Mg, Ca). The NEB, ranging from Ksh 217 — 778 and Ksh 224 — 833, was significantly (P = 0.001; 0.011) different. Positive control (Ksh 778) and poultry manure (Ksh 833) had the highest NEB, while charged biochar (Ksh 217) and compost (Ksh 224) had the lowest. This study highlights varied effects of charged biochar and organic fertilisers on lettuce production. The amendments approach enhanced productivity and promoted organic lettuce production. It also recommends adoption of poultry manure and long-term (residual) effects of charged biochar on lettuce production enterprises.