Curly lettuce production using cassava wastewater as a potassium source¹

Produção de alface crespa utilizando água residuária da mandioca como fonte de potássio

ABSTRACT

Cassava wastewater (CWW) is a natural biofertilizer successfully tested as a source of K in long-cycle crops; however, it still needs to be better evaluated in short-cycle crops. This study aimed to evaluate the use of CWW as a source of K in the growth, yield, and physicochemical quality of curly lettuce. The study was conducted in a greenhouse, in a randomized block design arranged in a 5 × 2 + 1 factorial scheme, with four replicates. Five CWW doses were evaluated as an exclusive source of K: 0, 60, 120, 180, and 240 kg ha^-1 of K₂O; two forms of application: 1-total dose at planting: 2-application of 50% of the dose at planting + 50% of the dose in topdressing, and an additional treatment: 100% mineral fertilization at 120 kg ha^-1 of K₂O dose, using KCl as the source. The number of leaves (NL), plant height (PH), fresh mass (FM), dry mass (DM), moisture (MO), ashes (ASH), fibers (FB), lipids (LIP), proteins (PTN), and carbohydrates (CHO) contents were evaluated. All agronomic attributes of lettuce showed lower values when fertilized only with CWW than mineral fertilization. Lettuce fertilized only with CWW, depending on total or split application and dose, showed higher ASH, FB, LIP, PTN, and CHO contents reaching 4.05, 3.97, 1.75, 7.11, and 3.63%, respectively, compared to mineral fertilization. The CWW can potentially be used as a complementary K source in lettuce cultivation, as its exclusive use does not replace traditional mineral fertilization.

Key words:
Lactuca sativa L.; Manihot esculenta Crantz; biofertilizer; sustainability

HIGHLIGHTS:

Lettuce’s agronomic attributes decreased when plants were fertilized only with cassava wastewater as a source of potassium.

Lettuce’s bromatological attributes were higher when plants were fertilized exclusively with cas-sava wastewater.

Cassava wastewater can be used as a complementary potassium source for lettuce, as it does not replace mineral fertilization.