Abstract
<p>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<sup>-1</sup> and four rates of humic acid (HA); control, 400, 800 and 1600 mg l<sup>-1</sup> 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<sup>-1</sup> were achieved the highest fresh and dry weight of outer leaves and head as well as total yield ha<sup>-1</sup>. Furthermore, the total chlorophyll content, T.S.S. and mineral uptake were improved with increase N fertigation rate up to 150 kg ha<sup>-1</sup>. Crisphead lettuce plants that treated by 800 mg l<sup>-1</sup> HA as drench gave the highest mean values of total yield per hectare (65.81 ton ha<sup>-1</sup>), 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<sup>-1</sup>. Generally, the results showed that lettuce plants receiving N fertigation up rate 150 kg ha<sup>-1 </sup>+ 800 mg l<sup>-1</sup> HA achieved the highest mean values of fresh and dry weight of outer leaves and head as well as total yield ha<sup>-1</sup> and chlorophyll content of crisphead lettuce plants.<strong></strong></p>
Highlights
Crisphead lettuce (Lactuca sativa L.) is a leafy crop belongs to the Asteraceae family
The result showed that increasing N fertigation rate up to 150 kg ha-1 lead to increase the outer leave:head ratio, whether as fresh or dry weight basis
Lettuce plants receiving N fertigation rate up to 150 kg ha-1 recorded maximum total yield ha-1 compared with the plants that treated with either 50 or 100 kg N ha-1
Summary
Crisphead lettuce (Lactuca sativa L.) is a leafy crop belongs to the Asteraceae family (formerly Compositae). Lettuce is one of the best-selling salad vegetable crops, especially in dry regions, such as Saudi Arabia. Most N fertilizers used through the drip irrigation system are a high solubility and the crop uses about 50% of the amount applied and the rest lost by lixiviation in the soil, or volatilization into the atmosphere. Under these conditions, the adding of humic acid to lettuce plants that grown in sandy soil, maybe a viable option to increase the size root system, which reflects on increase use efficiency of nitrogen fertilizer
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