The Growth, Yield, and Quality of Lettuce (Lactuca Sativa L.) as Influenced by Spent Mushroom Substrate and Inorganic Fertilization

Abstract

The research was conducted at the University of Ghana’s Soil and Irrigation Research Centre (SIREC) from July 2023 to September 2023. The study evaluated lettuce responses to different rates of spent mushroom substrate (SMS) manure and NPK (23-10-5) fertilizers. The experiment was laid in a Randomized Complete Block Design (RCBD) with four replications and nine treatments. Thus, poultry manure, different rates of spent mushroom substrate (SMS) manure, NPK and combinations of SMS manure and NPK. Data was analyzed using GenStat (12th Ed.), and means were separated using Tukey’s HSD. Results showed positive effects of soil amendments on lettuce growth. NPK at 400 kg/ha produced the highest average leaf number (24 in season one, 23 in season two at 6 weeks after transplanting). The highest average yields were obtained with NPK 400 kg/ha (47.1 Mt/ha season one; 48.6 Mt/ha season two), significantly higher than SMS alone. Integration of SMS manure and NPK improved growth and yield compared to SMS alone. Leaf nutrient concentrations (N, P, K) were unaffected by treatments. Post-harvest soil analysis showed increases in pH, nitrogen, and phosphorus, while electrical conductivity, organic matter, calcium, magnesium, and potassium remained unchanged. The study recommends that farmers adopt integrated SMS manure and NPK fertilizer use for optimum lettuce yield, with a preferred application rate of SMS manure at 20 t/ha combined with NPK 400 kg/ha as side-dressing. Due to delayed nitrogen release in SMS manure, it should be applied at least four weeks before transplanting, earlier than poultry manure.