Effect of N Fertigation Rates and Humic Acid on The Productivity of Crisphead Lettuce (Lactuca sativa L.) Grown in Sandy Soil

Lettuce is a slow-growing plant, which often accumulates 70-80% of it is head biomass and N uptake just during the last three to five weeks before the harvest. As well, add humic acid (HA) with N fertilizers is helping reduce the loss of N via leaching, especially in sandy soil. Therefore, the doses of N fertilizer and HA preferably add them in harmony with the requirements of different lettuce growth stages. This investigation aimed to study effect of three N fertigation rates; 50, 100 and 150 kg ha-1 and four rates of humic acid (HA); control, 400, 800 and 1600 mg l-1 as well as their interaction on the growth, head characters and mineral uptake (N, P and K) of crisphead lettuce. The results showed that lettuce plants receiving N fertigation rate up to 150 kg ha-1 were achieved the highest fresh and dry weight of outer leaves and head as well as total yield ha-1. Furthermore, the total chlorophyll content, T.S.S. and mineral uptake were improved with increase N fertigation rate up to 150 kg ha-1. Crisphead lettuce plants that treated by 800 mg l-1 HA as drench gave the highest mean values of total yield per hectare (65.81 ton ha-1), fresh and dry weight of outer leaves and head and N, P and K uptake as well as chlorophyll content and T.S.S. Whereas, the ratio of outer leaves- head as the dry weight base was a significant increase with an increase in HA rate up to 1600 mg l-1. Generally, the results showed that lettuce plants receiving N fertigation up rate 150 kg ha-1 + 800 mg l-1 HA achieved the highest mean values of fresh and dry weight of outer leaves and head as well as total yield ha-1 and chlorophyll content of crisphead lettuce plants.