Description
Brazil has over 80 million ha of tropical pastures formed with species of Brachiaria (syn. Urochloa), mostly grazed by beef cattle and with low fertilizer inputs, especially nitrogen. Recent investigations by our team show that stoloniferous legumes such as forage peanut (Arachis pintoi) and Desmodium ovalifolium are able to persist in mixed swards with Brachiaria brizantha (cv. Marandu) if grazing height is regulated (maximum 30 cm) so that radiation can reach the soil surface allowing stolons to take root. These legumes can persist in mixed pastures and produce milk or animal weight gains similar to the application of 120 to 150 kg N/ha/yr. In studies at the CEPLAC field station south Bahia State (16°39´S, 39°30´ W), N2O emissions from urine of dairy cattle were 0.47 and 0.76 kg N-N2O/ha/yr for a mixed forage peanut/Marandu pasture and Marandu monoculture + 120 kg N fertilizer ha/yr, respectively, equivalent to emission factors (EF) of 0.81 and 2.09%. N2O emissions from the N fertilizer were 2.70 and 0.24 kg N-N2O/ha (EFs of 4.10 and 0.40 %) for the two applications, respectively. N2O emissions from urine of beef cattle were 0.314 and 0.267 kg N-N2O/ha/yr for a mixed Desmodium ovalifolium/Marandu pasture and Marandu monoculture + 150 kg N fertilizer ha/yr, respectively, equivalent to EFs of 0.45 and 0.40 %. Annual N2O emissions from 3 x 50 kg N fertilizer were 0.30 kg/ha/yr. Preliminary results indicate that enteric methane emissions from cattle grazing a mixed forage peanut/Marandu pasture were 9 % lower per kg weight gain than those on an N-fertilized Marandu monoculture. Considering the total elimination of the fossil CO2 emissions associated with manufacture and application of N fertilizer, the substitution of 150 kg N by the mixed grass legume pastures represents a decrease in GHG emission intensity of over 20 %.
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Stoloniferous Forage Legumes for Sustainable Mixed Pastures in the Tropics
Brazil has over 80 million ha of tropical pastures formed with species of Brachiaria (syn. Urochloa), mostly grazed by beef cattle and with low fertilizer inputs, especially nitrogen. Recent investigations by our team show that stoloniferous legumes such as forage peanut (Arachis pintoi) and Desmodium ovalifolium are able to persist in mixed swards with Brachiaria brizantha (cv. Marandu) if grazing height is regulated (maximum 30 cm) so that radiation can reach the soil surface allowing stolons to take root. These legumes can persist in mixed pastures and produce milk or animal weight gains similar to the application of 120 to 150 kg N/ha/yr. In studies at the CEPLAC field station south Bahia State (16°39´S, 39°30´ W), N2O emissions from urine of dairy cattle were 0.47 and 0.76 kg N-N2O/ha/yr for a mixed forage peanut/Marandu pasture and Marandu monoculture + 120 kg N fertilizer ha/yr, respectively, equivalent to emission factors (EF) of 0.81 and 2.09%. N2O emissions from the N fertilizer were 2.70 and 0.24 kg N-N2O/ha (EFs of 4.10 and 0.40 %) for the two applications, respectively. N2O emissions from urine of beef cattle were 0.314 and 0.267 kg N-N2O/ha/yr for a mixed Desmodium ovalifolium/Marandu pasture and Marandu monoculture + 150 kg N fertilizer ha/yr, respectively, equivalent to EFs of 0.45 and 0.40 %. Annual N2O emissions from 3 x 50 kg N fertilizer were 0.30 kg/ha/yr. Preliminary results indicate that enteric methane emissions from cattle grazing a mixed forage peanut/Marandu pasture were 9 % lower per kg weight gain than those on an N-fertilized Marandu monoculture. Considering the total elimination of the fossil CO2 emissions associated with manufacture and application of N fertilizer, the substitution of 150 kg N by the mixed grass legume pastures represents a decrease in GHG emission intensity of over 20 %.
