Nitrogen fixation dynamics of Brachiaria decumbens and four shrubby legumes in a pasture system in Northeastern Brazil

Abstract

Nitrogen (N) fixation, herbage mass and botanical composition were measured in a silvopastoral system with shrubby legumes Bauhinia cheilantha, Gliricidia sepium, Leucena leucocephala and Mimosa caesalpiniifolia planted in grazed Brachiaria decumbens in Northeastern Brazil. A greenhouse study was conducted to determine the natural abundance δ15N of the legumes grown without soil N (B value), reported as 2.24‰ and 1.03‰ for G. sepium and L. leucocephala, respectively. In the field, G. sepium and M. caesalpiniifolia were significantly (p<0.05) larger then B. cheilantha and L. leucocephala and G. sepium and L. leucocephala fixed more N than the other legumes. Amount of fixed N in the grass ranged from 76.4% in the B. cheilantha paddocks to 58.2% in the M. caesalpiniifolia paddocks. The herbage mass of the B. decumbens pasture showed that control plots produced more grass in each time period then the legume-grass plots due to competition and shading.