LAUSR

About one-third of organic agriculture production in Brazil is carried out by smallholders, who seek to use low-cost organic fertilizers in their crops. In this study, we evaluated the nest refuse of leaf-cutting ants (NR) in the formulation of growing substrates for lettuce (Lactuca sativa) and arugula (Eruca sativa) seedlings. A completely randomized design with six treatments and four repetitions was applied. The treatments were basis growing substrate (CONT), commercial substrate (TropstratoHT®—TROP), and four formulations using NR of two species of leaf-cutting ants associated with 75 or 85% (volume fraction) of CONT. Substrates were submitted to chemical analysis for determination of macro- and micronutrients while plant vigor was evaluated considering plant height (PH), root length (RL), stem diameter (SD), dry mass (DM), and number of leaves (NL) at 15, 20, 25, and 30 days after sowing. The data were submitted to a chemometric evaluation by means of principal component analysis (PCA). Treatments with 25% of NR resulted in lettuce seedlings from 42 to 53% higher and with a twofold increase of dry mass compared to the commercial substrate (TROP) (P < 0.05). For arugula, similar results were found for PH and NL between TROP and the substrate with 25% of NR and these results differed significantly from the other treatments (P < 0.05). PCA revealed the formation of five groups of treatments, with TROP and two treatments based on NR presenting higher correlation with the nutrient content and plant vigor (P < 0.01). This study is the first to indicate the feasibility of nest refuse of leaf-cutting ants in the composition of substrates for organic agriculture in small-scale production.