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Inedible vegetable-oil based biodiesel in Northern Viet Nam 185
guidance noted that when planting Vernicia concurrently with another
annual crop on the same field, the use of separate fertilizer for Vernicia is
unnecessary (Vietnamese Academy of Forest Sciences, 2009). Consequently,
the amount of fertilizer required in Hibiscus monoculture was used as the
annual fertilizer input of the intercropping field. However, since Hibiscus
and Vernicia are supposed to be planted in low fertile soil, 100kgha 1 of urea
fertilizer use was set to ensure the growth of tree and seed yield. This assump-
tion was based on the application in Malawi, in which 50kg of nitrogen
1
(N) ha is applied to increase fruit yields (Morton, 1987). The dose of
100g DAP (diammonium phosphate) equivalent per plant was also applied
in Pongamia field to maintain and assure its seed production in low fertile soil
(Wanietal.,2006).Ontheotherhand,althoughformerpilotPongamiaplan-
1
tation in Quang Ninh Province applied the tree density of 3000 trees ha
could confirm their growth rate, the potential of seed production is still
unknown. Moreover, several scholars claimed that seed productivity of
Pongamia considerably depends on planting density (Niemiec, 2015; Syam-
suwida et al., 2015) and the tree density of up to 500 tree ha 1 was considered
to beappropriate (Murphy et al., 2012). Therefore the planting density of 500
trees ha 1 was adopted in the base case scenario of this study.
Hibiscus leaves and Pongamia and Hibiscus-Vernicia seed cake were
used to offset fertilizer use on the field since they have a high nutritional
composition (McClintock and El Tahir, 2004) and have been recognized
as excellent organic fertilizer (Do and Nguyen, 2003; Wani et al., 2006).
The amount of composts applied to the field was calculated from the nutri-
ent components of the leaves and seeds for each year according to the liter-
ature. Average nutrient compositions of Hibiscus leaves and Pongamia,
Hibiscus, and Vernicia seedcake are described in Table 6.7.
Table 6.7 Nutrient components in Hibiscus leaves, Pongamia oil cake, Hibiscus oil cake,
and Vernicia oil cake
Component Nitrogen (N %) Phosphorus (P %) Potassium (K %)
Pongamia oil cake a 5.21 0.56 0.91
Hibiscus fresh leaves b 2.08 1.17 0.29
Hibiscus oil cake c 4.94 0.63 0.03
Vernicia oil cake d 3.50 0.97 0.50
a
Data from Wani et al. (2006).
b
Data from Al Shooshi (1997) and Nnebue et al. (2014).
c
Average data from Al Shooshi (1997), Duke (1983), Hainida et al. (2008), McClintock and El Tahir
(2004), and Morton (1974).
d
Data from Do and Nguyen (2003).