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Phytotechnology with Biomass Production
mixture of extractables present in seed including proanthocyanidins and
vanillic acid. This makes it difficult to use seed clusters to enhance stands.
In controlled competition there appeared to be root competition and it was
also observed in field scale that shoot competition was a problem. Thus,
when using direct seeding, it proved a challenge to obtain good stands.
The relative price and success of rhizome vs plantlet propagation seem to
differ between situations and countries. Much of the variation in success may
depend on summer water and winter weather. Overplanting by 25%–50% may
be an economically viable alternative to assure an adequate stand (Boersma &
Heaton, 2014a).
5.2.2 Water
Adequate water is essential to establish growth of rhizomes. Available water
is decreasing in many areas while being found in excess in others. Caslin
et al. (2011) report that soil moisture must be at least 40% of field capacity at
planting. The rhizomes desiccate rapidly when kept at ambient temperature
without water. Drought at this stage is fatal. If rain is insufficient, supplemental water is necessary. Providing supplemental water to 1 ha of M. × giganteus
(>10,000 plants) can be costly. Drip irrigation would require 1.1 km of drip
tubing with nozzles at plant spacing (up to 1 m apart), plus additional fittings.
With drip irrigation, watering needed will depend on the soil water-holding
capacity within a zone comprising several liters surrounding each rhizome.
The equivalent of 10 cm depth of water in an area 15 cm in radius (7 L) will
wet soil to a depth of about 30 cm. This uses 70 m 3 of water for 10,000 plants.
To supply each plant with a supplemental 10 cm water uses 1000 m 3 of water
if using sprinkler irrigation.
For a first-year crop, drip irrigation can allow large savings if water is
expensive. During peak growth later in the establishment year, water use
may be greater than 5 cm depth wk −1 . There must be sufficient supply to have
significant percolation of water to depths greater than the root depth during
establishment, to encourage their downward growth. Roots of M. × giganteus
are reported to reach depths of >2 m, though the large majority of roots, when
water is available, remain much closer to the surface. Rhizomes of M. × giganteus are usually within the top 15 cm (Sage et al., 2015) (Figure 5.2).
In the study described by Kalinina et al. (2017), drip irrigation was used
in Turkey during second to fourth years, with sufficient irrigation (23 cm in
year 2) added to nearly match the potential evapotranspiration. The amount
of irrigation used in year 1 was not stated but it was enough to result in
rapid growth of the plants, so that yields, averaged over all trialed CVs that
were better in the first year than other sites, were also better in the second
year (>10 t ha −1 ), though not for lack of water in the more temperate settings
of other sites. The longer, warmer growing season in Turkey may have been
largely responsible for higher production. See discussion below about geography of factors for Miscanthus growth.