Seleção de estirpes de rizóbios para leguminosas de múltiplo uso em duas classes de solos ácidos da Amazônia Central

Abstract

In leguminous tree survival and early growth of seedlings after planting definite is favored significantly by inoculation with efficient strains of rhizobia. The production of vigorous seedlings and well nodulated allows final after planting, better competition with invasive plants, and the rapid resumption of growth in the field, which is important for reforestation with legumes. In this work, were selected two tree species of Fabaceae, in order to select efficient strains of rhizobia on N2 fixation for use as inoculum in two soils of central Amazonia. Were chosen to ingá-de-metro (Inga edulis) and palheteira (Clitoria fairchildiana). The soils used was Ultisoil, collected in agroforestry system, and soil Oxisoil in abandoned pasture. Prior to the test, so naturally available nitrogen depletion, cultured maize (Zea mays) variety 5110 for 45 days, after this period, the plants were cut close to the soil surface and then received a basic fertilization. The seeds of both species were germinated in drained boxes filled with washed sand and transplanted into bags with 2 kg of soil, kept in nursery. For both species were considered the following forms of N supply: plants without inoculation and without nitrogen fertilization, plants fertilized with mineral N (as urea) and inoculation of individual strains of rhizobia Collection of INPA. For ingá-de-metro was employed individual inoculation of 10 strains of rhizobia: 828, 831, 832, 833, 841, 842, 844, 847, 850 and 852. On the other hand, for the inoculation of palheteira was evaluated eight individual strains of rhizobia: 938, 941, 943, 944, 945, 949, 950 and 959. Strains were inoculated into liquid suspension, 5 ml applied to the base of the neck of transplanted. Plants were monitored monthly in growth and assessed at three months of nursery. We determined the biomass of leaves, stems and roots of plants after drying in an oven at 65 for 72 h and also the number, biomass and specific weight of the nodules. Were determined the concentration of leaf-N and N-total-cumulative by the method of Kjelhdal. The experimental design for ingá-de-metro was completely randomized design with factorial arrangement of 2 x 12 (2 soils and 12 forms of nitrogen supply), with 10 repetitions. Regarding palheteira, the design of the experiment was also randomized in this case, with a factorial arrangement of type 2 x 10 (2 soils and 10 forms of N supply), with 10 repetitions. It was demonstrated that the ingá-de-metro responds efficiently inoculation with selected strains, allowing the formation of seedlings nodulated well and fit the permanent planting. At 91 days, the plants were averages of 23.6 cm stem length, 4.7 mm diameter, 206 nodules plant-1 and 3.13% N in leaf biomass. The fertilization with mineral N inhibited the formation and development of nodules ingá. The symbiotic efficiency was demonstrated by a significant linear correlation between leaf biomass and nodules. The strains 831 and 844 showed potential for use as a microbial inoculant for ingá, to a efficient symbiosis established in the two soils studied. The palheteira showed adaptation to two soil conditions of the land surveyed, however, measures of growth and development were favored in Oxisol soil, and the number, nodule dry biomass and leaf-N concentration was higher in Ultisol soil. The N supply in the form of mineral-N inhibit the formation of nodules, discouraging the symbiotic process. On the other hand, inoculation of palheteira with rhizobia strains 943, 944, 945 and 949 favored the development of plants and provided high levels of N in the leaves, and were identified as the most potential for use as inoculant of this species in soils of land surveyed.