Methane and nitrous oxide emissions from cattle excreta on an East African grassland

Abstract

<p>Greenhouse gas (GHG) emission measurements from livestock excreta in Africa are limited. We measured CH₄ and N₂O emissions from excreta of six Boran (<i>Bos indicus</i>) and six Friesian (<i>Bos taurus</i>)steers near Nairobi, Kenya. The steers were fed one of three diets (T1 [chaffed wheat straw], T2 [T1 + <i>Calliandra calothyrsus</i>Meissner – 0.2% live weight per day], and T3 [T1 + calliandra –0.4% live weight every 2 d]). The T1 diet is similar in quality to typical diets in the region. Calliandra is a leguminous fodder tree promoted as a feed supplement. Fresh feces and urine were applied to grasslands and emissions measured using static chambers. Cumulative 28-d fecal emissions were 302 ± 52.4 and95 ± 13.8 mg CH 4–C kg^-1 dry matter for Friesen and Boran steers, respectively, and 11.5 ± 4.26 and 24.7 ± 8.32 mg N₂O–N kg^-1 dry matter for Friesian and Boran steers, respectively. For urine fromFriesian steers, the N₂O emissions were 2.8 ± 0.64 mg N₂O–N 100mL urine-1. The CH₄ emission factors (EFs) (246 ± 49.5 and 87 ± 12.7g CH 4–C yr^-1 animal^-1 for Friesan and Boran, respectively) were lower than the International Panel on Climate Change EFs (750 gCH 4–C animal^-1 yr^-1), whereas the N2O EFs (0.1 and 0.2% for the Friesian and Boran feces, respectively, and 1.2% for urine) were also lower than International Panel on Climate Change estimates.The low N content of the excreta likely caused the low emissions and indicates that current models probably overestimate CH₄ and N₂O emissions from African livestock manure.</p>