Publication Date

1993

Description

A pure Andropogon gayanus sward was compared with a Stylosanthes spp.-A. gayanus mixed sward in order to assess the benefit of introducing N2-fixing legumes on the long-term sustainability of grazed pastures. There was no difference between the total dry matter and animal production of the 2 pastures, although the legumes fixed 67-117 kg/ha of N in 1991 with 80% of the legume N obtained from N2 fixation. Litter deposition was 20-35% greater in the mixed sward and the % N in this litter was also higher, leading to twice the amount of N mineralised in the 0-5 cm layer compared with the pure grass pasture. Calculations using a simple N cycling model indicated that the introduction of the legume caused the annual N balance of the system to increase from -58 kg/ha of N to a zero or positive balance (-5 to +45 kg/ha of N).

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Importance of Legume Nitrogen Fixation in Sustainability of Pasture in the Cerrados of Brazil

A pure Andropogon gayanus sward was compared with a Stylosanthes spp.-A. gayanus mixed sward in order to assess the benefit of introducing N2-fixing legumes on the long-term sustainability of grazed pastures. There was no difference between the total dry matter and animal production of the 2 pastures, although the legumes fixed 67-117 kg/ha of N in 1991 with 80% of the legume N obtained from N2 fixation. Litter deposition was 20-35% greater in the mixed sward and the % N in this litter was also higher, leading to twice the amount of N mineralised in the 0-5 cm layer compared with the pure grass pasture. Calculations using a simple N cycling model indicated that the introduction of the legume caused the annual N balance of the system to increase from -58 kg/ha of N to a zero or positive balance (-5 to +45 kg/ha of N).