Resumo

GONZALE, P.J; FERNANDEZ, D; PLANA, R  e  CRESPO, G. Effects of the cultural antecedent on native mycorhizae and the productivity of the brachiaria pasture (Brachiaria decumbens cv. Señal). Pastos y Forrajes [online]. 2007, vol.30, n.1, pp. 1-1. ISSN 0864-0394.

The influence of the cultural antecedent on native mycorhization and the yield of the brachiaria pasture (Brachiaria decumbens cv. Señal) was evaluated; for that two 0,5 ha lots were selected, which were occupied for five years before sowing the pasture, in one case by short cycle crops (grains, tubers and vegetables) and in the other by permanent natural pastures (mainly species of the Bothriochloa-Dichanthium complex and Teramnus labialis). In each lot ten plots of 200 m² each were delimited, and in May, 2004, the brachiaria was sown in rows separated by 70 cm and with drilling, with a dose of 8 kg total seed ha^-1. After the establishment the pasture was cut every six and eight weeks in the rainy and dry seasons, respectively, and no chemical or organic fertilizers were applied. In each plot samples of root and soil from the rhizosphere were taken, in order to determine the mycorhizal structures of the pasture (percentage of colonization, percentage of visual density and number of spores per 100 g), as well as samples of the aerial biomass for determining the content and extraction of macronutrients, and the DM yield. The plots that had natural pastures as precedent crop showed significantly higher values (P<0,01) of colonization, visual density and number of spores per 100 g of soil, in the rainy as well as in the dry season. Likewise, a highly significant effect (P<0,01) of the cultural antecedent on the content and the extraction of macronutrients in the biomass, and on the pasture productivity, was observed. In the plots previously occupied by natural pastures the brachiaria reached the highest contents of N (1,30%) and P (0,20%) in the rainy season, as well as the highest extraction values of N, P and K and DM yields in both seasons, which exceeded in 20% those of the plots previously dedicated to agricultural crops. It is concluded that the natural mycorhization, the content and extraction of nutrients, as well as the yield of brachiaria, may be affected by the crop systems that precede the sowing of pasture.

Palavras-chave : Brachiaria decumbens; mycorhizae; yield.

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