Nutrient management for lettuce

This project, initiated in 2014, tested the effects of different N and K application rates on growth, yield, and quality of lettuce grown in Guangdong. The experiment consisted of 8 treatments in combinations of 4 application N rates (0, 135,180, and 225 kg N/ha), 4 K rates (0, 81, 108, and 135 kg K₂O/ha) and one P rate (54 kg P₂O₅/ha). An extra of 12 kg Mg/ha and foliar sprays of 0.2 borax solution were added to each treatment. Fertilizers were split 8 times so that 30% of the N and K along with all the P and Mg fertilizer was applied at the seedling stage, and the remainder of the N and P were split into seven topdressings with irrigation in the proportions of 10%, 7.5%, 7.5%, 12.0%, 8.0%, 12.5%, and 12.5%. Borax solution was sprayed at the 2nd, the 3rd and the 5th application timings.

Lettuce yield was boosted by addition of N fertilizer, leveled off at 180 kg N/ha and responded to K rates in a similar way (i.e., yield leveled off at 108 kg K₂O/ha). The treatment with optimal rates of N and K had the highest plant height and the highest yield of 16 t/ha, 1.7 t/ha (12%) and 2.2 t/ha (16%) more than the omission N and omission K treatment, respectively. In addition, this treatment also had the highest enzymatic activities for nitrate reductase and glutamine synthetase, indicating more active N metabolism. In terms of other lettuce quality measurements, none of these treatments significantly affected the content of soluble sugar, amino acids, nitrate, or vitamin C.