Optimization of Substrate and Nutrient Solution Strength for Lettuce and Chinese Cabbage Seedling Production in the Semi-Arid Environment of Central Myanmar

The growing population of tropical countries has led to a new awareness of the importance of vegetables as a source of essential foods and nutrients. The success of vegetable cultivation depends to a large extent on high-quality seedlings. This work aimed at evaluating the effects of different substrates and different nutrient solution concentrations on the development of lettuce and Chinese cabbage seedlings in a semi-arid tropical area. Three independent experiments were conducted at the Soil and Water Research Station at Yezin Agriculture University, Myanmar (Myanmar, 19.83° N; 96.27° E). In all experiments a randomized block design was implemented with four treatments and three repetitions. In the first experiment the adaptability of lettuce seedling to two substrates (namely a Hulls Manure mix composed by 50% of mature cattle manure and 50% of carbonized rice husk and a soil based substrate constituted by 70% local soil, 20% burned rice husk, and 10% fresh cattle manure) and two nutrient solutions with different electrical conductivities (ECs) (W₀.₁, stored rainwater with EC = 0.13 dS m⁻¹ and NS₁.₂, nutrient solution with EC = 1.20 dS m⁻¹) were tested. In the second and third experiments, two species (lettuce and Chinese cabbage) were assessed for their response to nutrient solution concentrations. In both crops, 4 fertigation treatments (W₀.₁; NS₀.₆; NS₁.₂; and NS₁.₈) were supplied, by modulating the concentration of a compound mineral fertilizer (15:15:15) in the following ranges: W₀.₁: 0 g L⁻¹, electrical conductivity (EC) 0.13 dS m⁻¹, NS₀.₆: 0.3 g L⁻¹, EC of 0.60 dS m⁻¹; NS₁.₂: 0.6 g L⁻¹, 1.2 dS m⁻¹ EC, and NS₁.₈: 0.9 g L⁻¹, 1.8 dS m⁻¹ EC. Adopting different substrates and applying different nutrient solutions significantly affected growth (fresh weight and leaf morphology) and some physiological parameters (stomatal conductance, leaf temperature, and leaf chlorophyll content) of lettuce and Chinese cabbage seedling. From the first experiment, the combination of the soil based substrate and NS₁.₂ treatments allowed us to improve the seedlings’ growth. In the second experiment, highest growth of lettuce and Chinese cabbage seedlings was associated with NS₁.₂ and NS₁.₈, respectively. The presented results allow for the optimization of both growing media and nutrient solution management when lettuce and Chinese cabbage seedling are produced in the Central Dry Zone of Myanmar.