Colonização micorrízica e fertilidade do solo submetido a fontes e doses de adubação nitrogenada em Brachiaria brizantha

Abstract

The feasibility and increase in the production of new cultivars can be obtained with the practice of nitrogen fertilization. The objective of this study was to verify the effect of sources and levels of nitrogen fertilization, concerning the depths, on the percentage of mycorrhizal colonization and soil fertility when covered by Brachiaria brizantha cv. Xaraés. A randomized blocks design was used and the treatments were under a 3 x 4 factorial scheme, regarding three nitrogen sources (urea, ammonium sulfate, and ajifer-L40) and 4 nitrogen levels (0, 100, 200 and 400 kg ha-1), studied at 2 different depths (0-0.10 and 0.10-0.20 m), with 3 replications. In each plot, the soil samples, composed of 5 simple samples, were collected, sieved, homogenized and sent for analysis. The use of ajifer and urea promoted higher production of shoot dry matter of B. brizantha cv. Xaraés. On the other hand, this dry matter showed reduction with the increase of N doses. The best fertilization dose was 100 kg ha-1 of N. The increasing doses of N employed, on the depth of 0-0.10 m, resulted in soil acidification and decreased the levels of MO, K+, Ca2+, Mg2+, SB and V%. Sporulation, but not mycorrhizal colonization, was stimulated by higher applied dosages.