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Miscanthus – the plant that tolerates poor soils

All farms have areas of poor soils. Some are simply a fertility issue, some are waterlogged part of the time, some have very low organic matter and some are so free draining that surface rooted plant such as pasture grasses cannot thrive. Providing the terrain is suitable for harvesting machinery, these are all sites where Miscanthus can be grown. The main site requirements are machine accessibility to the site, adequate soil depth, gentle terrain and annual rainfall of at least 600 mm per year. Warm summers are helpful as is reliable rainfall. More rainfall means higher production.

The experience of Miscanthus New Zealand Limited (MNZ) is that productive Miscanthus crops can be grown without additional fertiliser on what is normally regarded as poor soils. In our experience, although Miscanthus can grow better on good soils, particularly in its establishment year it is also very tolerant of poor soils and actually helps to improve those soils. The depth of the rooting of Miscanthus – up to 2 m depth – and the fact that it builds up soil organic matter by a significant and measurable amount, means that after a Miscanthus crop has been grown on the site for some years, the soil is at least as good as it was when the Miscanthus stand was planted.

In the UK, the norm is for farmers to plant Miscanthus on areas that they regard as unproductive. Often farmers are so pleased with the result that they then expand planting onto more productive areas of the farm. We know of one farmer who followed this route and ended up with the whole farm planted in Miscanthus.

A quote on the Terravesta website that came from a UK farmer who has 26 ha of Miscanthus on what he described as “underproductive fields” said:

“Miscanthus has numerous positive attributes including long-term financial security, robust growing markets and environmental benefits. With Miscanthus you have to take a long-term view and look at the guaranteed returns available from an upfront investment.”

That effectively sums up the position for Miscanthus in temperate regions anywhere in the world. In some ways it is similar to forestry in that it can turn what otherwise would be unproductive land, into productive land. But unlike forestry the revenue flow starts from the end of the second growing season and apart from the harvesting costs there are then virtually no ongoing costs with Miscanthus.

There is one place in New Zealand where Miscanthus was established on a site that was formerly in radiata pine plantation forest. The biggest problem that this has created is for harvesting where residual pieces of log or branch which were not cleared properly prior to establishment, remain. But in terms of growth, the low nutrient status of the site does not seem to have limited the development of the Miscanthus at all.

At another site near Helensville, Miscanthus has been grown for over eight years on a very sandy site that adjoins Woodhill forest – a sand stabilising forest. The Miscanthus here has performed well with productive harvest in the order of 20 tonnes per hectare of dry matter per year. On this site, soil tests were taken prior to the planting of Miscanthus and were repeated four years later. The results from the second assessment were virtually identical to the results from the first assessment. This showed that in spite of no fertiliser having been applied, the quality of the site remained no worse than it was prior to establishment. The intention of MNZ is to get this assessment repeated this year because we suspect that the soil will have been improved, with a much higher soil organic matter content than there was originally.

A further site near Huntly that was specially selected as a trial planting area because it was considered by the landowners to be “marginal land” has also been harvested annually from year two. The harvest quantity in 2018 – after nine years of annual harvesting was the equivalent of 26 tonnes of dry matter per hectare. Nothing has been done to this crop since it was established, other than harvesting it each year.

And in Hawkes Bay, at one site, production was as high as 33 tonnes per ha without any irrigation. Another site there that has a freer draining soil was not quite as good as that.

The economics of growing such Miscanthus crops is unparalleled. With a harvest cost of roughly $35 – $70 per tonne of dry matter and a price at farm gate of $200 – $300 per tonne, the net return per hectare makes most alternatives look pathetic. Then when you take into account that this is marginal land with poor soils and there has been no expenditure since the establishment year, it becomes blindingly obvious that most farmers with such land of suitable terrain should be growing at least some Miscanthus.

Next in the series will be an article about how just growing Miscanthus is better than carbon neutral.

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