Dynamics of animal performance, and estimation of carbon footprint of two breeding herds grazing native neotropical savannas in eastern Colombia

Carlos A Ramírez-Restrepo,Raul R Vera,Idupulapati M Rao

doi:10.1016/j.agee.2019.05.004

Abstract

The savannas of eastern Colombia located in the Orinoco river basin represent 18% of the Latin American neotropical savannas, and those areas that are tillable and closer to markets are subject to considerable anthropic pressure in the quest for intensification. Historically, and even today, beef cattle production constitutes the main land use, and much of it is subjected to extensive management. This paper describes for the first time, the use of cattle grazing experiments to assess methane (CH4) emissions from neotropical savanna-based beef breeding systems, and with the support of published research conducted next to them, estimates of the carbon (C) footprint in carbon dioxide equivalents (CO2-eq) for the whole system. Over 5 years and covering complete reproductive cycles, a conventional weaning (CW) herd system was compared to an early weaning (EW) herd system, that represented a modest degree of more intensive savanna management. Differences were found between the two management practices in total CH4 emissions, emission intensities [kg CH4 kg –1 calf born and kg CH4 kg –1 liveweight gain (LWG)] and emission efficiencies (kg CO2-eq kg –1 calf born and kg CH4 kg –1 LWG), that mostly associated with the different lactation lengths. When both herd systems were carried over until calves, later yearlings, reached to 25 months of age, the differences in favor of EW breeding herd system were diminished. The calculated C footprint in (CO2-eq) of both management practices was near neutral subjected to a number of assumptions and the use of limited published information on savanna C stocks and CH4 and nitrous oxide (N2O) emissions from soil, and it is posited that both herd systems were nearly in equilibrium. The available data and results show the need for further information on the neotropical savanna C stocks and C sequestration potential of soils of the Orinoco river basin. More reliable datasets regarding below-ground C inputs and CH4 and N2O emissions from soil are needed to provide a useful basal benchmark for, and approach to, future analyses of environmental impact of more intensive beef herd systems in the region.

Highlights

Savannas have been extensively managed by humans for different production purposes, driving ecological processes such as fire frequency and biomass accumulation, and affecting the carbon (C) cycle (Grace et al, 2006)
“ it is stated that one of the objectives of the study was 'to quantify the carbon footprint (CF) of beef breeding herds subjected to conventional weaning (CW) vs. early weaning (EW)', it doesn't appear that a 'whole system analysis' has been performed
“Lines 23-26: Regarding the claim that: 'This paper describes for the first time, use of cattle grazing experiments to assess CH4 emissions from savanna-based beef breeding systems....' Is it correct? There are at least few previous studies focusing on CH4 emissions from savanna-based systems in Northern Australia (Bray et al 2016 The Rangeland Journal, 2016, 38, 207-218, Bray et al 2014 Animal Production Science, 2014, 54, 1988-1994)

Summary

Introduction

Savannas have been extensively managed by humans for different production purposes, driving ecological processes such as fire frequency and biomass accumulation, and affecting the carbon (C) cycle (Grace et al, 2006). Reducing C emissions -the so-called “carbon footprint”- is critical to confront global challenges of both climate change and land degradation. This is mainly because savanna systems may directly mitigate greenhouse gas emissions by (i) increasing soil organic C (SOC; Sanhueza and Donoso, 2006; Fisher et al, 2007; Rao et al., 2015); (ii) reducing ruminant methane (CH4) emissions per unit of livestock product (Vélez-Terranova et al, 2015; Durmic et al, 2017); and (iii) decreasing nitrous oxide (N2O) emissions (Byrnes et al, 2017; Chirinda et al, 2019). Well-drained savannas in Colombia evolved from natural ecosystems inhabited by indigenous communities (Navas-Ríos, 1999), to extensive grazing of beef breeding herds (Huertas-Ramírez and Huertas-Herrera, 2015)

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