Impacts of future climate scenarios on the balance between productivity and total greenhouse gas emissions from pasture based dairy systems in south-eastern Australia

摘要

The challenge for agriculture is to increase production in warmer climates in order to meet the demands of an increasing global population, while also meeting targets for reduced greenhouse gas (GHG) emissions. Our aim was to quantify the net effect of future climate scenarios on the productivity and total GHG emissions from pasture based dairy systems in 4 regions of south-eastern Australia using the biophysical model DairyMod. In each region, a single paddock in the grazing rotation of a dairy farm was simulated. This paddock was grazed at a stocking density of 50 lactating dairy cows/ha for a period of one day each time the pasture biomass reached 2.2 t dry matter (DM)/ha. In this way, the annual stocking rate (i.e., cows/ha) reflected the number of times that the paddock was grazed annually. No supplementary feed was offered to the animals. Model estimates of annual pasture intake, stocking rate, milk production, CH4 and N2O emissions were compared at each site in a baseline climate (1971-2000) and 3 future climate scenarios representing increasingly warm and dry conditions, termed the '2030', '2070 mid' and '2070 high' scenarios. At Kyabram (northern Victoria) summer irrigated perennial pastures were modelled in the baseline scenario, with supplementary irrigated annual pasture systems simulated in the baseline scenario for comparison, and in the future scenarios. At Terang (south-western Victoria), Ellinbank (south-eastern Victoria) and Elliott (north-western Tasmania) dryland perennial pastures were modelled. In dryland systems, increased pasture intake, stocking rate and milk production was modelled in all future scenarios for the cool temperate climate at Elliott. with reduced production in the '2070 mid' and '2070 high' scenarios at Ellinbank and Terang. At Kyabram, productivity of the annual system was lower than the perennial system in the baseline scenario, but increased in future climates, assuming adequate irrigation water availability. Among sites and climate scenarios, annual per cow GHG emissions were 3.4-5.5 t CO2 equivalents (CO(2)e), with CH4 making 0.63-0.89 of total emissions. Annual emissions per unit area ranged from 2.6 to 13.1 t CO(2)e/ha among sites and climate scenarios, and generally reflected stocking rates. However, in the future scenarios, there were changes in N2O emissions at dryland sites due to increased direct N2O losses and lower indirect N2O through volatilisation and leaching. Annual emission intensities ranged from 7.5 to 10.9 t CO(2)e/t milk protein plus fat among sites and climate scenarios. The lowest emissions intensity was at Elliott, which also had little change in future climates. At Terang and Ellinbank, the emission intensity was 8.8 t CO(2)e/t MS in the baseline climate, but this increased by more than 20% in the 2070 high scenario. Results suggest that pasture based production systems can continue as the basis of the dairy industry in north-western Tasmania, but lower production and higher emission intensity at Terang and Ellinbank suggest that systems adaptations are required to meet future GHG emissions reduction goals.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture - Finding a Balance between Food and Emissions, Guest Edited by TA McAllister, Section Guest Editors: K.A Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson