Legumes up profit, lower GHG

By Sandra Taylor

In Livestock6 Minutes

When it comes to reducing greenhouse gas emissions onfarm there is no silver bullet, but better feeding and legume-based systems tick a lot of boxes.

Lincoln University’s Professor Derrick Moot, who completed his post-doctoral study on climate change in the United KIngdom, says all the work he and the Dryland Pastoral Research Group have done over the past 30 years has been about reducing the environmental footprint of sheep and beef farms.

“If the work around legumes and better feeding hadn’t happened, we wouldn’t have seen a 30% reduction in emissions intensity over the last 30 years, that is the kg CO2/kg meat produced.”

In a paper charting the changes in New Zealand’s red meat production in the past 30 years (1990-2020), Moot and co-author Rob Davison, executive director of Beef + Lamb New Zealand’s Economic Service, describe how the expansion of the dairy industry, thanks to the advent of centre-pivot irrigation on traditionally summer-dry areas, meant a sharp increase in the area of pastoral land that was converted to dairy production (1.4 to 2.2 million hectares). Correspondingly, there was a sharp decrease in the number of sheep and beef farms from 19,600 in 1990-1991 to 9165 in 2021.

As part of this transition to dairy farming and dairy support, the red meat sector lost much of its traditional flat and rolling finishing country.

Ewe numbers plummeted from 40.4 million in 1990/91 to 16 million in 2020/2021 and the grazing land area occupied by sheep and cattle decreased from 12.4 to 7.7m ha. Conversely, the area of non-grazed tussock and woody vegetation and forestry increased from 1.3 to 1.7m ha.

Against this backdrop and despite being pushed back to more marginal country, the productivity of the sheep industry increased, with the national average lambing percentage jumping from 100% in 1990 to 132% in 2021, while carcase weights lifted from an average of 14.4kg to 19kg.

While there have been several reasons for increased productivity, Moot says the main one has been the focus on the quantity and quality of feed being grown on hill country farms, particularly the use of legumes such as lucerne and clovers.

Legume-based systems tick many boxes in helping reduce greenhouse gas (GHG) emissions. They overcome the need for nitrogen with minimal urea, so reduce nitrous oxide emissions and they drive animal growth rates which mean reduced GHG emissions per unit of product.

Greater productivity per ewe, with increased scanning and lambing percentages, has meant a reduction in ewe numbers therefore decreasing total GHG emissions.

This has enabled farmers to retire poorer land to sequester carbon.

More importantly, these systems have given farmers hope that they were able to reduce their GHG emissions while increasing productivity, Moot says.

He believes across the sector, there is a general reluctance to promote productivity, but without productivity gains, GHG emissions from the red meat sector would be significantly higher.

While there has been an industry focus on trying to find a way to cut GHG emissions through the development of vaccines or additives, Moot believes more thought should be given to the whole farm system and the impact feeding, particularly legumes, has on that system.

In 2019, Professor Moot reported on one study carried out on a Mackenzie Country property which showed how pre-weaning growth rates in Merino lambs had increased from 190 to 290g/head/day over a 10-year period. This was due to the expansion of the area of lucerne grazed. Higher lamb growth rates shortened the lactation phase by 35 days and contributed to reduced methane emissions.

Similarly, an industry wide analysis, carried out by scientists at AgResearch, showed how increasing lamb growth rates from 100g/day to 300g a day on high-quality feed, reduces the days to finishing from 100 to 33 and the amount of methane produced per kilogram of product from 303 to 165.

It also reduced the energy consumed per lamb from 1300 megajoules of metabolisable energy to 726 MJ ME, a 79% reduction.

Central to the challenge of reducing GHG emissions in the red meat sector, while maintaining or increasing productivity, is the efficient use of nitrogen.

Nitrogen is the limiting nutrient on many of the pastures used for animal production and legumes can be instrumental in correcting that deficiency, Moot says. While not a silver bullet, legumes will be an increasingly important tool as red meat producers grapple with ways to reduce their total farm emissions.