Soils intensively cultivated with vegetable crops may show potassium accumulation and this may cause damage to the environment and the plant. Viewing to evaluate the response of lettuce ‘Amanda’, of the crisphead group, to five doses of potassium (0, 25, 50, 75, and 100 kg/ha K2O) in a potassium-rich Rhodic Eutrudox soil, two experiments were carried out at two different planting times from 05/05 to 07/23/2008 (PT1) and from 03/24 to 05/14/2010 (PT2), in Jaboticabal, state of São Paulo, Brazil. The experimental units were distributed in the field, according to a randomized complete block design with four replications. Potassium content in the leaves (KL), number of leaves (NL), leaf area (LA), the plant aerial part fresh weight (APFW), the plant aerial part dry weight (APDW), and potassium content in the soil (KS) were determined. Significant interactions of the factors K rates and PT were not observed upon evaluated characteristics. The PT affected all characteristics. In PT1, the plants showed larger values of NL, LA, KL, and KS and in PT2, larger values of APFW and APDW. The KL adjusted to quadratic model with maximum (61.8 g/kg) obtained with 55 kg/ha K2O, while KS after experiments adjusted to linear model, showing 1.5 mmolc/dm3 when the crop was fertilized with K and 1.9 mmolc/dm3 when fertilized with 100 kg/ha de K2O. The potassium fertilization had no influence on NL, LA, APFW, and APDW, and therefore, it was not recommended to fertilize lettuce with K in soils with high content of K. Aiming to keep the K content in the soil in the initial levels, the amounts of K accumulated by lettuce crop should be applied, in this case, 100.8 and 202.7 kg/ha K in the first and second planting time, respectively.
Key words: Growing season, growth, Lactuca sativa, production.
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