Stacking Interventions Enhances Carbon Removals and Profitability of Livestock Production Systems

Abstract

While previous studies have primarily examined the impacts of singular interventions on GHG emissions reduction and carbon dioxide removals (CDR), few studies explore complementarities and antagonisms when multiple interventions are simultaneously operationalized. Here, the aim is to examine how stacking of two pathways for mitigation-CDR, via soil organic carbon (SOC) accrual and GHG emissions avoidance via antimethanogenic feed additives-impacts net GHG emissions associated with sheep production. A nonlinear programing approach is invoked to elicit optimal combinations of grazing management and antimethanogenic feed additives to maximize farm profit and/or minimize net GHG emissions. It is shown that stacking multiple interventions realizes that greater abatement and profit do any singular intervention. Adoption of 3-NOP feed supplement with 15- and 30-paddock high stocking rate systems is the most prospective stacked intervention for concurrent profit maximization and emissions minimization. It is contended that (1) increasing payments for farming of carbon and ecosystems services relative to that of wool and meat will stimulate participation in carbon markets, (2) economics of participation in carbon markets tend to be more favorable for larger farms than smaller farms due to economies of scale and (3) adoption of optimal grazing management and antimethanogenic feed additives can realize more profit from sheep production and carbon farming than enterprises that only derive income from sheep production.

Keywords: co‐benefit; manure; nitrous oxide; optimization; organic carbon; sequestration.

Figure 1

Conceptual design of the study. Green represents input data from peer‐reviewed data experiment and farm case studies. Red represents simulated data used as an input to the programing model, yellow represents published data from SILO^{[ 64 ]} or peer‐reviewed papers,^{[ 43} , ⁵⁶ , ⁵⁸ , ⁵⁹ , ^{65 ]} while blue represents the programing model structure and constraints. Fencing costs were based on those of multi‐paddock systems.^{[ 30 ]} Stage 1 represents initialization computations, while Stage 2 represents the optimization of grazing management and feed additive decisions to maximize profit and/or minimize GHG emissions.

Figure 2

Self‐replacing flock dynamics used in each programing model. Simulations were conducted with Merino ewes joined to terminal sires. Sheep sold include ewes and wethers at two years, while cast for age (CFA) ewes represent ewes culled from the main breeding flock after five years. Blue arrows represent ewe replacement cohorts, while red arrows represent cohorts destined for sale. Black arrows represent main breeding flock activities, such as lambing of breeding ewes, two‐year‐old ewes in year one becoming three‐year‐old ewes in year two et seq.

Figure 3

Trade‐offs between profit and GHG emissions reduction. Circles represent the small farm, squares represent the large farm. Light blue, red and dark blue depict results from Models I, II, and III, respectively, for the initial scenario. Model I optimized the combination of grazing treatment and antimethanogenic feed additives to maximize profit and minimize net GHG emissions, simultaneously. Model II optimized grazing treatment and antimethanogenic feed additives to maximize profit from sheep and wool sales. Model III optimized grazing treatment and low‐emission feed additives to minimize net GHG emissions. Models II and III included profit from sheep and wool sales, while total profit of Model I included income from sheep and wool production as well as GHG emission reduction, assuming a carbon price of $38 per t CO2‐e. Light and dark green points depict carbon price scenarios at $50 and $100 per t CO₂‐e, respectively. Yellow, orange, pink, and purple points depict four sheep price scenarios (decreasing 20%, 50% or increasing 20%, 50% respectively). Dark blue, orange and red circles overlap on the small farm, while light green, dark blue, red and light blue squares overlap on the large farm.

Figure 4

Cumulative profit and emissions intensity for three optimized management scenarios for small and large farms. Numbers on x‐axis represent years. Model I optimized grazing management and feed additives to maximize total profit and minimize net GHG emissions, simultaneously. Model II optimized grazing management and feed additives to maximize profit from sheep and wool sales. Model III optimized grazing management and feed additives to minimize net GHG emissions. Blue, purple, and green bars represent cumulative profit from Models I, II, and III, respectively. Orange, red, and pink circles represent cumulative emissions intensity from Models I, II, and III respectively.

Figure 5

Optimal grazing and antimethanogenic feed management regimes. Carbon price of Model I was set at $38 per t CO₂‐e; 15P and 30P represent 15‐ and 30‐ paddock systems, fast/slow rotation represent two to four or four to eight days per grazing event, while high/low stocking rates were 13.6 or 8.8 DSE ha⁻¹, respectively. Bars represent grazing treatments, circles represent antimethanogenic feed additives. Other grazing and feed management are not shown.

Figure 6

Trade‐offs between mean percentage GHG mitigation from SOC accrual and enteric methane reduction over ten years with variation in carbon price. Results drawn from optimal grazing and antimethanogenic feed additive management of Model I when all inputs remained constant, and two carbon price scenarios ($50 and $100 per t CO₂‐e) were compared with initial carbon price ($38 per t CO₂‐e).

Figure 7

Impacts of sheep price on mean emissions intensity and average flock size. P represents baseline sheep price, while 0.5P, 0.8P, 1.2P and 1.5P represent four scenarios with reduced/increased price. Bars (flock size) relate to the left axis and circles (emissions intensity) relate to the right axis.

Figure 8

Impact of carbon price on average number and age of sheep sold. Results are plotted for Model I for carbon prices of $38 per t CO₂‐e and two future price scenarios ($50 and $100 per t CO₂‐e). Blue bars represent average flock size, yellow bars represent average sheep age.