Sustainable Urban Farming: Effects of Organic Manure on Lettuce Growth and Soil Fertility

Abstract

Rapid urbanization has reduced available agricultural land, creating an urgent need for sustainable food production systems such as urban organic farming. This study aimed to evaluate the effects of manure type and dosage on lettuce (Lactuca sativa L.) growth and yield under urban organic farming conditions, identify the optimal application rate, and assess its contribution to soil fertility and sustainable nutrient management. Two separate experimental series were carried out under a Completely Randomized Design (CRD). Each series involved a single type of manure (chicken or goat) combined with five application levels (10, 20, 30, 40, and 50 tons ha⁻¹), and every treatment was repeated three times. Lettuce seedlings were transplanted into polybags containing 5 kg of soil mixed with the respective manure treatments. Growth parameters—including plant height, leaf number, and stem diameter—were measured weekly, while yield components (fresh and dry biomass, root length, and total yield) were assessed at harvest. Data were analyzed using ANOVA, and mean differences were tested with LSD at the 5% level. The results revealed that goat manure significantly (p < 0.01) enhanced all growth and yield parameters compared with chicken manure, which had no significant effect due to its high C/N ratio and immature composition. The optimal performance was observed at 30–40 tons ha⁻¹ of goat manure, with 30 tons ha⁻¹ identified as the most efficient rate, producing comparable yield with lower input use. Goat manure improved vegetative growth, nutrient uptake, and overall productivity, highlighting its potential as a sustainable organic amendment for urban lettuce farming. Moderate application of goat manure (30–40 tons ha⁻¹) is recommended to improve yield performance and promote sustainable manure recycling in urban organic agriculture systems. The findings of this study suggest that incorporating organic fertilizers in urban farming can enhance crop productivity and soil health, thereby supporting more sustainable urban agricultural practices, improving food security, and providing environmental benefits through reduced reliance on synthetic inputs.