Optimizing Lettuce Productivity using Chicken Manure under Different Planting Densities and Varying Nitrogen Levels

To study the potential of organic fertilizers as partial substitutes for mineral nitrogen to enhance lettuce productivity and minimizing excessive nitrogen use and promoting sustainable agricultural practice, a field experiment was implemented during two consecutive winter seasons of 2016/2017 and 2017/2018. Lettuce was used as an experimental plant. The experiment was laid out in a split-split plot design, as the main plots were assigned to four levels of organic fertilizer (Chicken manure ChM) at rates of 0, 10, 20, and 30 ton ha-1. The sub-plots received four nitrogen fertilizer levels (urea, 46% N) at rates of 0, 90, 180, and 270 kg N ha⁻¹, while the sub-sub plots were designated for two planting distances: 20 × 60 cm and 40 × 60 cm. The measured parameters included total fresh and dry yield, total head yield, head weight and diameter and NPK contents. The results showed that the most superior treatment combination across both seasons was the application of 30 tons ha⁻¹ ChM combined with 270 kg N ha⁻¹ and the closer planting distance, which led to the highest total and marketable yields. It is also noteworthy that the treatment involving 30 tons ha⁻¹ of chicken manure combined with 180 kg N ha⁻¹ and the closer planting distance (20×60 cm) produced results that were not significantly different from those obtained with the treatment that received 270 kg N ha⁻¹ without any organic manure under the same planting distance. This finding highlights the partial substitution role of organic manure in supplying nitrogen.