Low-Cost Soilless Lettuce Production under Saline Irrigation Using Local Substrates and a Commercial-Fertilizer Nutrient Solution

Soilless cultivation is a practical option for vegetable production in arid regions where soil salinity and freshwater scarcity limit conventional farming. However, the high cost of imported substrates and specialized nutrient solutions restricts adoption by small growers. This study assessed lettuce (Lactuca sativa L.) grown in local low-cost substrates under fresh and saline irrigation. The experiment was conducted at Shambat, Sudan, using a two-factor randomized complete block design with three replicates. Four media were compared: gravel, coarse sand, a Conocarpus-derived biochar-sand mixture, and local clay soil. Fresh water and saline water gradually adjusted to 3 dS m⁻1 were used. A nutrient solution was prepared from commercial fertilizers available in local markets. Under saline irrigation, the biochar-sand medium recorded the highest plant height (18.20 cm), leaf number (13.80 leaves plant⁻1), leaf area (178.4 cm2), shoot dry weight (12.10 g), root dry weight (2.90 g), and water-use efficiency (1.44 g L⁻1). Coarse sand also performed well, with 16.80 cm plant height, 158.7 cm2 leaf area, and the greatest water saving relative to clay soil (18.75%). Clay soil recorded the lowest values under saline irrigation, including plant height (12.10 cm), leaf area (98.6 cm2), shoot dry weight (6.50 g), and water-use efficiency (0.68 g L⁻1). The integrated saline performance index ranked biochar-sand first (100/100), followed by coarse sand (74.70/100), gravel (54.71/100), and clay soil (0/100). The biochar-sand medium requires repeated washing before use because residual soluble salts may restrict early establishment. These findings support the use of local substrates and commercial fertilizers as a practical pathway for low-cost lettuce production under moderate salinity in arid environments.