Sheep manure compost: a viable growing substrate for lettuce seedling production

Purpose: The substantial use of peat as a nursery substrate leads to the destruction of ecologically important peat bogs, necessitating the search for sustainable and suitable alternatives. In this study, we assessed the suitability of sheep manure-based compost as a potential substrate to either partially or complete replace commercial peat in the production of lettuce (Lactuca sativa L.) seedlings. Methods: Five different substrate treatments were used: 100% peat (100% P) served as the control; 100% compost (100% C); 25% C/75% P; 50% C/50% P; and 75% C/25% P. The study followed a completely randomized design, with sixteen replications for each treatment level. Various parameters, including seedling emergence, seedling survival, seedling growth, seedling vigor index, Dickson’s quality index, among other variables, were analyzed. Results: Seedling emergence ranged from 87.5 to 100%, with no significant differences among the substrate treatments, suggesting that seedling emergence and initial establishment can be successfully achieved in sheep manure-based compost. For seedling growth, sheep manure-based compost, whether used alone or in combination with peat, also resulted in similar or even better outcomes as compared to the control. For example, in the 100% compost treatment, seedlings exhibited comparable diameter growth and total seedling biomass to those of the control, or 100% peat. However, seedling height was 7.6% greater in the 100% compost substrate when compared to the control, demonstrating the potential growth-promoting effects of utilizing sheep manure-based compost as a growing medium. Conclusions: During our study we found that the quality of seedlings produced in all tested substrates was similar to that of the control. Therefore, as a compost, sheep manure, a locally and widely available resource, shows promise as a viable nursery substrate, potentially entirely replacing the expensive, non-renewable, and environmentally sensitive peat currently being used in nurseries for producing lettuce seedlings.