Soil-Water-Plant Relations and Growth Response of Curly Lettuce to Integrated Microbial and Reduced Chemical Fertilization

Abstract

This study evaluated whether microbial fertilizer combined with a 50% reduction in chemical fertilizers can maintain or improve growth performance of curly lettuce (Lactuca sativa L. var. crispa) under greenhouse conditions. The study was arranged in a completely randomized design with seven treatments and four replications: control without fertilizer application (C), optimum chemical fertilization (OF), three combined treatments consisting of 50% reduced chemical fertilizer plus microbial fertilizer at 5 mL L⁻¹ (RCF_MF5), 10 mL L⁻¹ (RCF_MF10), and 20 mL L⁻¹ (RCF_MF20), and two sole microbial fertilizer treatments at 10 mL L⁻¹ (MF10) and 20 mL L⁻¹ (MF20). Irrigation was applied at approximately four-day intervals by restoring the depleted soil moisture to field capacity based on pot weight. Seasonal evapotranspiration during the experimental period was calculated based on the difference between pot weight at field capacity and pot weight before irrigation, and the seasonal evapotranspiration during the curly lettuce growing period was determined as 214.2 mm. The microbial fertilizer consisted of a consortium of Streptomyces species. Growth parameters, including fresh weight, dry weight, and head diameter, were measured at harvest. Treatment effects were highly significant (P