Increased Nitrogen Retention and Reduced Methane Emissions of Beef Cattle Grazing Legume vs. Grass Irrigated Pastures in the Mountain West USA

Jennifer W Macadam,Karen A Beauchemin,Andrea I Bolletta,Raul D Guevara Ballesteros,Xin Dai,Lance R Pitcher,Juan J Villalba

doi:10.3390/agronomy12020304

Jennifer W Macadam, Karen A Beauchemin + Show 5 more

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https://doi.org/10.3390/agronomy12020304

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Abstract

Grazing studies were carried out over a 5-year period using pregnant cows, yearling calves and 2-year-old heifers to investigate the influence of diet on intake, methane (CH4) emissions and retention of nitrogen (N). Monoculture legume (birdsfoot trefoil, BFT and cicer milkvetch, CMV) or grass (meadow bromegrass, MBG) pastures were rotationally stocked, and during year 4 and year 5, treatments were contrasted with total mixed rations (TMR) fed in confinement. The sulfur hexafluoride (SF6) method was used to continuously measure enteric CH4 emissions. Intake was greater on legume pastures and on TMR than on grass pastures, and enteric CH4 emissions per unit of intake were lower on legumes compared with grass pastures. Legume pastures had elevated non-fiber carbohydrate (NFC) concentrations (400 g kg−1 dry matter; DM) typical of perennial legumes cultivated in the Mountain West. A N balance calculated in 2017–2018 demonstrated that N retention was greater for TMR and legume than grass pastures. Enteric CH4 emissions of grazing cow herds account for the majority of greenhouse gas (GHG) emissions from beef production and can be significantly reduced by using highly digestible forage legumes. The N retention of legumes can potentially enhance the efficiency of N use, thereby increasing the sustainability of grasslands.

Highlights

Introduction iationsThe sustainability of U.S agriculture is threatened by the degradation and/or loss of ecosystem services due to global warming and anthropogenic interventions such as reduced biological diversity; water and air pollution; and loss of soil quality [1,2,3]
Digestibility was greater for the legumes than for the grass; the TDN of legumes was always greater than 700 g kg−1 DM, and in 2017 and 2018 it was greater than that of the high-forage confinement total mixed ration (TMR) (Table 2)
We investigated enteric CH4 emissions and the retention of N in cows, calves and heifers because beef cows produce the greatest proportion of the emissions from the cow herd [15], and we sought to determine the potential of perennial legumes to reduce beef system greenhouse gas (GHG) by contrasting cattle grazing legume monocultures with cattle grazing grass monocultures or those fed with TMR in confinement

Summary

Introduction

The sustainability of U.S agriculture is threatened by the degradation and/or loss of ecosystem services due to global warming and anthropogenic interventions such as reduced biological diversity; water and air pollution; and loss of soil quality [1,2,3]. The sustainability of beef production has come under considerable scrutiny given increased concerns over the use of cereal grain for livestock feed [4,5] and the contributions of CH4 and N2 O from livestock production to global warming [6]. U.S wetlands and grasslands have been converted to cropland for the production of annual feed grains, reducing ecosystem services provided by these lands. Of the annual grains produced in the U.S, 70% is used as livestock feed and approximately 35% of the grain consumed by livestock is fed to beef and dairy cattle [7]. Cereal grains require annual nitrogen (N) fertilization and periodic replacement of soil phosphorus and other mineral nutrients that are removed as they are harvested.

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