Abstract
The intensive use of synthetic fertilizers in horticultural systems has raised environmental and economic concerns, prompting the search for sustainable alternatives for nutrient management. Liquid digestates derived from the anaerobic digestion of animal manure represent a promising option within circular economy frameworks. This study evaluated the growth and yield response of romaine lettuce (
Lactuca sativa
L. var.
longifolia
) to liquid digestates derived from guinea pig, pig, and cattle manure in northeastern Peru. A completely randomized design with a factorial arrangement was used, considering digestate type, application dose (2%, 4%, and 6% v/v), and application frequency (every 7 and 10 days). Growth and yield traits, including plant height, collar diameter, fresh weight, and number of leaves, were evaluated at commercial maturity. Significant differences among treatments were observed for all evaluated variables. The highest overall agronomic response was obtained with pig-manure digestate applied at 6% every 10 days (T12), reaching 28.00 ± 1.01 cm in plant height, 3.45 ± 0.35 cm in collar diameter, 790.83 ± 77.51 g of fresh weight per plant, and 51.08 ± 1.62 leaves per plant. Application frequency had a limited effect, although the 10-day interval produced the best overall response when combined with pig-manure digestate at the highest dose. These results indicate that liquid digestates, particularly pig-manure digestate, may serve as a promising alternative nutrient source for romaine lettuce grown under alkaline highland greenhouse conditions.