Formulações do tipo “bokashi” como fertilizantes orgânicos no cultivo de hortaliças

Abstract

Six pairs of plant residues based on a carbon source and a nitrogen source were evaluated as organic fertilizers for vegetable crops (lettuce and rocket). The resulting “bokashi” type fermented composts were the following: wheat bran + castor bean cake (FT/TM), wheat bran + gliricídia -leaves and tiny shoots (FT/GL), elephant grass + castor bean cake (CE/TM), elephant grass + gliricídia (CE+GL), sugarcane bagasse (crushed culms) + castor bean cake ( BC/TM), and sugarcane bagasse + gliricídia (BC/GL). All the mixtures where inoculated with either Embiotic® or Kefir. A control-treatment also was included in which the composts were not inoculated. For the first part af the study the composts were evaluated to chemical composition, pH reaction and electric conductivity. Bioassays using millet as a test-plant were performed in order to avaluate the disposal of nitrogen ando also too as long as their ability to stimulate biological activity by means of three indicators: carbon microbial biomass, soil basal respiration and metabolic quocient. Significant differences were detected among the composts for all analyzed characteristics. Inoculations with the commercial product Embiotic® or with Kefir cultures maintained in brown sugar aqueous solution did not differ from each other or even when compared with the non – inoculated control treatment. Results obtained from the millet bioassays indicated potential of the fermented composts to promote vegetative growth. In the second part of the study the organic composts, except for those having sugarcane bagasse as one of the components, were added to the soil previously to lettuce transplants placement in the field. Each compost incorporated amount was calculated on the basis of its contribution with 100 kg N ha-¹. Lettuce agronomical performance under organic farming was positively influenced by additions of the composts, differing from the absolute control treatment in which plots had not received any kind of fertilization. Following lettuce harvest, rocket transplants occupied the corresponding experimental plots, however, no residual effects could be demonstrated due to organic composts additions to the previous lettuce crop. Chemical and biological soil attributes were affected by the composts in different levels regardless of the microbiological inoculant employed. In a subsequent field experiment only the FT/TM x Embiotic® and the CE/GL x Kefir composts were compared. Dosages of such composts varied from 0 to 400 kg N ha-¹ applied to the soil before rocket transplants wears placed. Rocket crop showed positive responses in terms of vegetative growth parameters correlated to the offered dosages of both composts. Soon after rocket harvest lettuce transplants occupied the same, experimental plots. In this case lettuce showed significant improvements in growth derived from residual effects of the incorporated composts during rocket previous crop. The efficacy of fermented composts was related to their composition based on specific sources of carbon and nitrogen. Organic residues able to be obtained in situ, represented by dried and ground shoot biomasses of elephant grass and gliricídia, showed potential to replace composts formulated with industrial inputs, such as wheat bran and castor bean cake; for organic vegetable crops ( lettuce and rocket) production.