Application of Microorganisms Isolated from Compost and Digestate as Biofertilizers to Improve the Growth of Lettuce

Lettuce (Lactuca sativa L.) is a popular vegetable, low in calories, fat and sodium, contains minerals, fiber, vitamin C and polyphenols. Bacillus simplex (Bs) isolated from a compost, Glutamicibacter arilaitensis (Ga) isolated from a digestate, and a mixture of both microorganisms (Bs-Ga 50:50) were used as biofertilizers of lettuce crops, during spring and summer 2019, and compared with a commercial fertilizer (7-17-17 N-P-K, C+) and unfertilized (Cb) crops. Lettuce yields were higher in spring than in summer. The spring plants biofertilized with Bs, Ga and Bs-Ga were between 32.5 and 44.0% taller than C+, and between 18.6 and 28.9% higher than Cb plants; the fresh weight of biofertilized plants was 80-94% higher than C+ and 36-46% than Cb plants; the protein content of biofertilized plants was 30-70% higher than C+ and 40-46% higher than Cb plants. After week 5, bolting was observed in C+ and Cb summer lettuces, but in plants inoculated with Bs, Ga and Bs-Ga, the bolting was delayed 2 weeks. In week 7, all the chemically fertilized plants were bolting, and less than 30% was observed in biofertilized plants. Bolting of lettuce plants is undesirable because the plants produced are unmarketable. Compost and digestate are sources of plant growth-promoting bacteria as Ga and Bs that can be used as microbial biofertilizers of lettuce and substitute chemical fertilizers.