Irrigation Levels, Biochar and Cultivars Effects on Soil Physical Properties and Growth of Lettuce (Lactuca sativa L.)

Abstract

A field experiment was undertaken during the 2024–2025 cropping season within the eco-touristic forest site affiliated with the College of Agriculture and Forestry, University of Mosul, aiming to elucidate the interactive effects of deficit irrigation, biochar soil amendment, and varietal differences on growth and physiological responses of lettuce (Lactuca sativa L.). The experimental framework was structured as a factorial arrangement embedded within a split-plot system under a randomized complete block design (RCBD). Main plots were assigned to two distinct cultivars of imported lettuce (Rama and Nader), while sub-plots were factorial arranged to accommodate three irrigation regimes 50%, 75%, and 100% of field capacityand two biochar application levels (0% and 0.5% w/w). Biochar, produced from a designated biomass feedstock, was incorporated into the soil matrix during the pre-transplantation phase. The experimental matrix comprised 12 treatment combinations (3 irrigation × 2 biochar × 2 cultivars) replicated thrice, yielding a total of 36 experimental units. Statistical evaluations were conducted following the prescribed design structure, and mean comparisons were executed using Duncan’s Multiple Range Test at a 5% probability threshold (p ≤ 0.05). The results demonstrated that biochar application at 0.5% significantly enhanced several soil physical indices, notably increasing the liquid limit, plastic limit, mean weight diameter (MWD), and aggregate stability. Parallel improvements were recorded in physiological traits, including elevated leaf chlorophyll concentrations, increased dry matter accumulation. Additionally, irrigation regimes set at 75% and 100% of field capacity consistently outperformed the 50% level in all measured vegetative and physiological traits. Notably, the Rama cultivar exhibited superior performance over Nader, particularly in chlorophyll content and plant stature, suggesting inherent genotypic advantages under the tested conditions.