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Plantain crops yield reduction in soil nitrous oxide levels
SYSTEMS PLANTAIN TRIALS
AgResearch principal scientist Cecile De Klein with the trial plots of plantain at Invermay near Dunedin.
AgResearch trials near Dunedin may be a solution for dairy farmers to reduce greenhouse gas emissions. Karen Trebilcock reports.
Trial plots of plantain grown by AgResearch at the Invermay campus near Dunedin might be one of the keys to solving dairy’s greenhouse gas problem.
Although plantain is well known to reduce nitrogen in urine when it is eaten by cattle, AgResearch principal scientist Cecile De Klein said it appears there may also be something happening in the soil.
The trial plots at Invermay, grown for the past three and a half years, show 30% less nitrous oxide (N2O) is emitted from urine patches on soils growing plantain compared with areas growing ryegrass/ clover mixes.
“There is something in the sward, something in the soil where the plantain is growing, that changes the amount of nitrous oxide emitted,” she told farmers at a DairyNZ Explore Your Options field day in late March.
“We do know the plant structures, including the roots, are very different to grasses and clovers but we do not yet know why less nitrous oxide is entering the atmosphere from the soils these plants are growing in.”
Figures crunched at Anne-Marie and Duncan Well’s dairy farm near the Invermay campus showed stitching in 30% of plantain into pastures reduced nitrogen leaching losses by 15%, and nitrous oxide by 5% using Overseer modelling.
Even replacing only 10% of the pasture sward with plantain reduced nitrous oxide emissions by 2%.
Due to the cost of stitching plantain, there was also a 2% loss of operating profit.
With little research on how plantain holds up in southern, heavy soils, and how it performs putting milk into the vat, Duncan said he was unsure if he would add to the plantain already growing on the farm.
Other modelling using their farm showed wintering cows in a barn changed greenhouse gasses only slightly, as did wintering on instead of wintering off.
Young stock are grazed off the 217ha effective farm with all cows wintered off except for 45 of the 665-cow herd and the modelling included the off-farm grazing.
Plantain growing in one of the trial plots at Invermay.
Anne-Marie said winter grazing had caused them “sleepless nights”.
“We know there are fewer winter graziers out there but if we’re forced into a position of having to winter at home, the modelling shows it would not have a huge difference on greenhouse gasses overall which is a relief.”
Retiring some of the milking platform and planting it in cereals also changed little. Increasing pasture production to replace grain fed in the dairy by raising nitrogen fertiliser from 99kg/ha/year to 190kg/ha/year was the only scenario that increased profit.
However, it also increased nitrous oxide emissions by 17%.
Duncan said the fastest and easiest way to cut greenhouse gasses (methane and nitrous oxide) on the farm was by reducing the stocking rate (currently at 3.1 cows/ha) and growing less grass to feed them but producing the same amount of milk.
The farm has been chasing PW with its LIC breeding plan and he said they were starting to see the results of more efficient cows converting feed to milk which was lowering their figures.
The farm’s N leaching loss (kg N/ha/year) was 9 with methane at 9.157, N2O at 2.326 and CO2 at 1.327. The purchased N surplus (nitrogen which is brought in as either imported feed or fertiliser less nitrogen that leaves the farm as either meat or milk) is 41. Farmers can find their greenhouse gas emissions on Overseer by clicking on ‘reports’ and then ‘GHG’.
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