The use of bananas on dairy farms has shown strong potential as a new forage system and for taking up nutrients from effluent water discharge, especially potassium.
AgResearch has reported on the first 18 months of a trial of bananas on a Northland dairy farm, funded by the Our Land and Water Science Challenge.
The research team said no major red flags were identified in this short investigation.
More work is now needed on the understanding of nutrient cycling, including estimates of nitrogen loss and the grazing and harvesting strategies.
Most importantly, will cattle eat banana leaves and stems as a regular summer forage supplement to mitigate drought?
New Zealand cows do seem to like fruit and leaves of banana plants, as reports from overseas indicated they would.
Graeme and Carol Edwards have a 125ha effective farm at Opouteke, near Pakotai in mid-Northland, running 250 high BW cows on once-a-day (OAD) milking, System 2.
In late 2018, a small banana plot of 70 stems was planted alongside the effluent storage pond, which had been recently upgraded with a weeping wall.
The Misi Luki variety banana stems, now being grown around the north for their fruit, were irrigated by the pond green water with a drip delivery over the summer months.
Graeme and Carol’s son Paul Edwards, a dairy scientist, alerted AgResearch to the trial plot and suggested that measurements and basic management for forage be undertaken.
Graeme says the possibility of replacing or supplementing turnips with a nutritious green feed would address the drier and warmer summers.
It would also require less cultivation, lower soil carbon losses and reduce the risks of effluent irrigation.
Potentially just 4% of the farm planted in bananas could use all the green water, optimise effluent storage and avoid unconsented discharges and provide a large supplementary fodder source.
Grant Rennie, from AgResearch Ruakura, says banana plants grow quickly at the peak of summer and are relatively deep-rooted and drought tolerant.
The funded research measured the rate of growth and the quality of the existing plot, tested whether leaves and stems are nutritionally appropriate as cattle feed and if the plants can take up nutrients from green water.
The dry matter percentages of petioles and leaves and of stems, were measured at an average of 16.3% for petioles and leaves, with a standard deviation of 5%, and 8.3% for stems, deviation 1.3%.
Two groups of 15 plants were measured in a cutting trial, to see if cutting out large central stems would result in increased growth in the remaining stems.
They may also send up new stems and increase total growth in the plot.
The total number of stems in the cut group was similar to the uncut group, suggesting the cut plants only replaced the cut stems.
Cut stems that had not yet begun their reproductive cycle also regrew quickly from the centre between September and January.
Future longevity of plants under cutting and/or grazing needs further investigation but the regrowth potential is 10 tonnes-plus of dry matter when planted at 1600 stems a hectare.
Tropical plantations of bananas in Queensland have annual fruit harvests of 30 tonnes or more, so there is room for more growth and production in sub-tropical Northland.
Samples were taken and tested for feed quality, which show banana plants are low in protein, much like maize or fodder beet, low in fibre and high in water soluble carbohydrate.
The weighted average metabolisable energy was estimated at 10.4 megajoules per kilogram of dry matter.
The digestibility at 64% is similar to various silages and the non-dietary fibre is encouragingly low.
Graeme says cows were happy eating the leaves but struggled with the stems, which may have to be cut into chunks to assist the cows.
Soil samples at four depths were taken to see how minerals were moving through the soil profile after a season of green water application.
Potassium was 20 at the surface level, reducing to 2 at the 30 to 45cm depth.
Total nitrogen began at 0.49% near the surface and fell to 0.20% at depth.
“Without being able to estimate a mineral mass balance (amount applied less amount taken up in plants) these results give some confidence that there is nothing unusual occurring”, the AgResearch report said.
“There doesn’t seem to be any unexpected accumulation of nitrogen or potassium but it warrants further investigation, particularly under harvesting or grazing where significant amounts of nutrients will be removed from the site.”
Two minor matters were flagged for more investigation – damage to the growing corn by toppling the plant during grazing and some pest damage at the base, probably by pūkekos.