Lettuce needs nitrogen and potassium supplement during its expansion period.

During the elongation and expansion period, lettuce needs sufficient nitrogen and potassium supply to expand rapidly. The specific casting is as follows:

Nitrogen fertilizer and potassium fertilizer are applied once at the initial stage, middle stage and later stage of lettuce elongation and expansion, urea 15 - 20kg, potassium sulfate 8 - 10kg or potassium nitrate 20 - 25kg are applied every mu, and after mixing with clear water or biogas slurry or decomposed human and animal manure water 150 - 200 times, the fertilizer solution is evenly sprinkled in the soil around the root of lettuce plant, and the fertilizer solution completely penetrates into the soil and does not flow out.

??? In addition, 0.3% urea, 600 times amino acid potassium mixture or 0.5% potassium nitrate aqueous solution should be sprayed on the leaves every 7~10 days during the growth and expansion of lettuce, and continuously sprayed for 2~3 times. Spray all leaves evenly, starting with drops of water, and replenish nitrogen and potassium from the leaves.