GHG Emissions Reduction
The re-designing of a farm system to reduce greenhouse gas emissions
Changes in management of Bill and Shirley Wright’s South Canterbury sheep and cattle farm over the past two decades have resulted in a substantial reduction in GHG emissions intensity (Greenhouse gas output per kg of product sent off the farm). The recent use of crops with lower nitrate loss during a drought has also helped reduce nitrate leaching. And while not all sheep and beef farms have the same management flexibility, the results reflect industry-wide reductions in emissions intensity and show that increasing the resilience and financial viability of farms does not preclude environmental benefits.
Bill and Shirley run sheep and cattle on 380ha near Cave, South Canterbury. Much of the farm is wheel tractor country with some areas suitable for cropping. When they bought the property in 1991, sheep comprised 90% of the livestock. Today, says Bill, the mix has changed to 80% cattle.
“We are running about 700 dairy cattle including bulls and dairy grazers along with 1000 ewes. We rear bull calves and take some of them through to two-year-olds. The dairy grazers generally come on as calves and stay here for 18 months. We also trade beef from time to time but we have no breeding cattle,” says Bill. “We grow kale and fodder beet, about 30 ha in all. Most of that goes back into barley in spring, some for silage and some for grain. There’s also about 10 ha of maize for summer grazing.”
Rainfall averages about 600mm but some years are dry – last year only 422mm fell. Like many dry land farmers the Wrights have, in the past, been at the whim of markets during a drought and have had to sell stock as stores. Today they minimise that risk by growing summer crops – barley, maize, and about 70 ha of lucerne.
Aware of the potential environmental effects of cropping, Bill uses direct drilling for all crops and avoids disturbing the soil except for some surface cultivation after winter feeding. This reduces losses of soil carbon and precious moisture.
Feeding the winter crops is potentially the greatest source of nitrate leaching and strategies to hold stock off during wet weather have been effective. Findings from projects looking at low N-loss cropping may lead to Bill looking at alternative crops and sowing another crop straight after harvesting or feeding the previous crop to minimise leaching.
Over the past two decades the Wright’s environmental concerns have led to their fencing off waterways and planting shelterbelts, and fencing river terraces to allow native bush to regenerate. They have also made significant changes to their farming systems. Apart from the dramatic change in sheep/cattle ratio they have virtually done away with ryegrass and have sown pastures comprising fescue, white and sub clovers, plantain and chicory. They also now grow a significant amount of lucerne.
“We rotationally graze all year round apart from at lambing time, and that can be complex when you’ve got seven or eight mobs of stock,” says Bill. “We stock according to the feed available as far as we can and make stocking decisions or change policy as we go. That's where the maize and silage come in. Our stock flexibility is in the numbers of lambs and bulls. The least flexible stock are the dairy grazers and we have set systems up so that if we get short of feed we can keep them here using grazing maize, barley and grass silage.”
The changes to pastures, crops and livestock classes have made the farm business more flexible, more suited to a drought prone climate and certainly more financially and environmentally sustainable, but what has been the net effect on the environment? The Wright’s records dating back to the early 90s have allowed scientists to estimate changes in GHG emissions over time.
Dr Robyn Dynes, a farm systems scientist and Science Impact Leader with AgResearch, says their analyses show that between 1991 and 2014 the Wrights’ farming system increased its efficiency and reduced GHG emissions intensity (CO2 equivalents per kilogram of product) by 18%.
“Emissions in 1991 were 16.9 kg of CO2 per kilogram of product, and in 2014 it was down to 13.8kg. The farm has changed from predominantly lamb and wool production in 1991 to a flexible land use policy, with a high proportion of cattle, including dairy support,” says Robyn. “The amount of product leaving the farm has increased because of greater production from use of forages and adoption of new technologies.”
“To understand the current emissions from the farm we focused on setting up a robust farm systems model that gave us estimates of the nitrogen balance and emissions to water, along with greenhouse gas emissions to air. Then we went back to the 1991 records to compare nitrogen and greenhouse gas outputs.”
Estimates were derived from models based on extensive research in specialist facilities where measurements of dry matter eaten by animals were correlated with measured GHG emissions and nitrogen losses.
As well as showing that losses have reduced over time, the data indicate which farm practices are contributing most to emissions. This enables farmers to consider changes that would mitigate the losses, and much of the research to support these decisions is being developed in Forages for Reduced Nitrate Leaching programme. Bill had focused on nitrate leaching because it was most important to him, but the data raised other questions: What forage combinations might give you better outcomes than you have now? What mix of species would give you more shoulder season feed? When is the best time to run bull beef?
The study’s results definitely indicate a win-win, says Robyn. “The farm is improving its efficiency – capturing more of those key nutrients and turning them into products to export out the gate. That is a win in terms of both losses to water and losses to the atmosphere,” she says.
“The other win is that we are identifying the parts of their systems where they have opportunities to make change, so if they grow a fodder beet crop our researchers suggest they should follow it with a catch crop to pick up some of that nitrogen before it ends up in the waterways. Likewise ensuring that you are maintaining high quality feed, because that means less total intake for the same performance and less methane emitted.”
“Studies like these help farmers to understand what parts of their farm systems have highest GHG or nitrate losses. This knowledge means they can target mitigation options to reduce losses from their farm,” she says.
The study of gas emissions was carried out by scientists from AgResearch with funding from the NZAGRC (New Zealand Agricultural Greenhouse Gas Research Centre) and the MPI. Research around the nitrate leaching has been done under the Forages for Reduced Nitrate Leaching (FRNL) programme with funding from DairyNZ, the Foundation for Arable Research, AgResearch, Plant and Food Research, Landcare Research and the Government.