Fungos micorrízicos e doses de fósforo em alfafa (Medicago sativa L.)

Abstract

With the purpose ofevaluating the responses of arbuscular mycorrhizal fungus andphosphorus fertilization on the yield andquality of the forage ofalfalfa Medicago sativa L. cv. Crioula, in soü of low natural fertility, was conducted an experiment in a greenhouse of the Department of Animal Science of the Universidade Federal de Lavras - UFLA, Lavras (MG). A soü classified as Red Dark Latosol (LE), epialic, A moderate, very clayey texture, flatrelieÇ caming from the UFLA campus and collected inthe0-20 cmdeep layer. The experimental design utüized was the completely randomized, in a 5 x 3 factorial arrangement, with 5 replications, amounting to a total of15 treatments, they being 5 leveis of P (30, 60, 120,180e 240mgofP/kg of soü) and3 conditions of soü (natural soü, deinfested by fumigation with methyl bromide, deinfested and inoculated with the arbuscular mycorrhizal fungus - AMF - Glomus etunicatum), applied toMedicago sativa L. cv. Crioula. The cuts were performed whenever the plants reached 20% offlowering, for determination ofthe aerial part dry matter yield, crude protein yield (CPY) and accumulated amounts of P, K, Ca, Mg and S, in the experimental period. After the last cut, root dry matter yield, mycorrhizal colonization rate, spore density in soil and nodule number were evaluated. The results obtained allwed to verify that the increase in the doses ofphosphorus fertilization (P), the soil conditions (S) and the (P) x (S) interation, influenced signifícantly aU the variables studied. Phosforus fertilization provoked an increase inthe dry matter yield ofthe aerial part and root, incrude protein yield and inthe accumulation of P, K, Ca, Mg and S. That finding was signifícantly more pronounced in the soü under inoculationwith AMF. It was verifíed that alfalfa is highly dependent onthe micothrophic condition to maximize its yield, mainly at the intermediary leveis of phosphorus fertilization. Elevated doses ofP reduced mycorrhizal colonization and soü spore density. P and the triple symbiosisalfalfa - Rhizobium - AMF, increasedthe nodulenumber in the roots.