Sisal/Agave - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 336

Table 15.2 Summary of
yields (Mg ha 1 ) for Agave
species (As reviewed in Davis
et al. [ 2 ])

n a Species Mean yield ( Standard error)

A. deserti 3 6.1 ( 0.4)

A. fourcroydes 3 14.0 ( 1.5)

A. sisalana 2 14.5 ( 2.5)

A. lechuguilla

( 10.9) 2 14.7

A. tequilana 5 23.7 ( 0.8)

A. salmiana 7 23.8 ( 5.4)

A. mapisaga 4 31.6 ( 3.8)

a n

¼ the number of studies used to calculate mean yield

Propagation

Commercially produced Agave are harvested before the flowering stage, are often
sterile hybrids, and even if fertile they are highly heterozygous, and would therefore
produce highly variable stands from seed. Therefore, plants are not typically
propagated by seed but instead are propagated asexually to provide uniform clonal
material. Seeded plants are also disadvantaged because they have a tendency to be
more sensitive to drought and sudden temperature changes and require more years
to reach harvest maturity than asexual propagules [ 5 , 14 , 30 ]. Asexual propagation
can occur by harvesting offset rhizome shoots or bulbils from a plant inflorescence
or through micropropagation by tissue culture. These methods provide more robust
plantlets and result in lower variation in plants across a field than a seeded crop [ 5 ].
The flowering stalk must be allowed to form in the case of propagation by
bulbils, but a single stalk can produce thousands of plantlets. Thus, nearly a hectare
of Agave plants can be planted from one or two mother plants. Sisal plants produce
~2,000 bulbils on a single stalk that can be harvested by simply shaking the plant
and collecting the fallen bulbils from the ground. This method will produce more
uniform plantlets than propagation from offsets, where only a few plantlets which
are typically of variable size can be harvested from a mother plant at a time. The
advantage of propagation from offsets is that one need not wait until the plant
matures to collect the plantlets. Offsets can be harvested annually, and these are
then typically kept in a nursery before planting in the field [ 31 ].
Harvest of Agave plantations is usually accomplished with manual labor and is
therefore an economic challenge for commercially scaled production for biofuel.
Nu˜ez et al. [ 23 ] reviewed the economic viability of Agave production for biofuel
assuming the methods that are currently used for tequila production are transferable
to Agave bioenergy feedstock production. The economic returns from Agave
feedstock production cannot compete with those realized by the tequila industry,
and manual labor costs incurred during the harvest phase of production limit the
economic competitiveness of Agave against other biofuel feedstocks [ 23 ]. This will
of course depend on the labor costs in the region chosen for cultivation.