observed in wild palms. Nutrient deficiency, especially the combined deficiency,
i.e. potassium deficiency and deficiency in microelements such as zinc and copper, is
widely observed both in the wild sago palms and those grown in the cultivation, in
both the peat soil and sandy soil (Kakuda et al. 2015). Although obvious boron
deficiency is often seen in an oil palm, it has not been reported in a sago palm yet
(Kakuda et al. 2015).
There are distinct effects of nutrient application on their concentration in the plant
tissues. However, the effects of fertilizer application in the range of usual rate on the
palm size such as the palm height, the number of leaves or the amount of trunk
growth are unclear in many cases. Fertilizer application may improve the nutrient
content in the leaf as reported by Nitta et al. (2000, 2003) although its effect on the
palm size is unclear in some cases. According to Kakuda et al. (2005), it is possible
that the applied fertilizers do not improve the growth of the parent palm because they
promote the growth of suckers instead as described above. Therefore, the sucker
growth needs to be examined further to clarify the influence of fertilization on sago
palm management in the field.
17.5.3 Nutrient Competition and Symbiosis
From a viewpoint of nutrient competition between sago palms and weeds,
Yanbuaban et al. (2007) reported that among 30 odd plant species found in the
peat soil of Narathiwat, southern Thailand, grass weed (Leersia hexandra) and sedge
weed (Fimbristylis umbellaris) were the main weeds that affected sago palm growth.
L. hexandra severely inhibits sago palm growth by shading the sago palm leaves and
preferentially absorbing phosphate and zinc, which tend to be deficient in peat soils.
Taking into account the nitrogen source for plants grown in peat soils, Kakuda et al.
(2015) suspected that both the sago palm and the weed absorb nitrogen fixed by
symbiotic microbes, ergo the N problem occurs. Shrestha et al. (2006) reported the
nitrogen fixing activity in different parts of sago palm and the characterization of
aerobic nitrogen fixing bacteria colonizing sago palms. The same also applies to
phosphorus, the contribution of symbiotic microbes such as arbuscular mycorrhizal
fungi (AMF) should be investigated considering a recent study on colonization of
roots in sago palm seedlings associated with mycorrhizal inoculants (Asano et al.
2019).
As described above, the impact of fertilizer application to the main stem of parent
palm remains unclear and appropriate fertilizer management for compensating
nutrient deficiencies in peat soils has not been established yet. Kasuya (1996) and
Miyazaki et al. (2011) reported that roots concentrate under the trunk in a shallow
soil layer. This kind of information must be considered in establishing the appropriate cultivation management in terms of both fertilization and irrigation. On the other
hand, Watanabe (2015) suggested that considering the rather inefficient growth
enhancement effect on sago palms, increased methane fluxes, and a possibility that
N application influences the generation of nitrous oxide, which is another
498
H. Ehara et al.
i.e. potassium deficiency and deficiency in microelements such as zinc and copper, is
widely observed both in the wild sago palms and those grown in the cultivation, in
both the peat soil and sandy soil (Kakuda et al. 2015). Although obvious boron
deficiency is often seen in an oil palm, it has not been reported in a sago palm yet
(Kakuda et al. 2015).
There are distinct effects of nutrient application on their concentration in the plant
tissues. However, the effects of fertilizer application in the range of usual rate on the
palm size such as the palm height, the number of leaves or the amount of trunk
growth are unclear in many cases. Fertilizer application may improve the nutrient
content in the leaf as reported by Nitta et al. (2000, 2003) although its effect on the
palm size is unclear in some cases. According to Kakuda et al. (2005), it is possible
that the applied fertilizers do not improve the growth of the parent palm because they
promote the growth of suckers instead as described above. Therefore, the sucker
growth needs to be examined further to clarify the influence of fertilization on sago
palm management in the field.
17.5.3 Nutrient Competition and Symbiosis
From a viewpoint of nutrient competition between sago palms and weeds,
Yanbuaban et al. (2007) reported that among 30 odd plant species found in the
peat soil of Narathiwat, southern Thailand, grass weed (Leersia hexandra) and sedge
weed (Fimbristylis umbellaris) were the main weeds that affected sago palm growth.
L. hexandra severely inhibits sago palm growth by shading the sago palm leaves and
preferentially absorbing phosphate and zinc, which tend to be deficient in peat soils.
Taking into account the nitrogen source for plants grown in peat soils, Kakuda et al.
(2015) suspected that both the sago palm and the weed absorb nitrogen fixed by
symbiotic microbes, ergo the N problem occurs. Shrestha et al. (2006) reported the
nitrogen fixing activity in different parts of sago palm and the characterization of
aerobic nitrogen fixing bacteria colonizing sago palms. The same also applies to
phosphorus, the contribution of symbiotic microbes such as arbuscular mycorrhizal
fungi (AMF) should be investigated considering a recent study on colonization of
roots in sago palm seedlings associated with mycorrhizal inoculants (Asano et al.
2019).
As described above, the impact of fertilizer application to the main stem of parent
palm remains unclear and appropriate fertilizer management for compensating
nutrient deficiencies in peat soils has not been established yet. Kasuya (1996) and
Miyazaki et al. (2011) reported that roots concentrate under the trunk in a shallow
soil layer. This kind of information must be considered in establishing the appropriate cultivation management in terms of both fertilization and irrigation. On the other
hand, Watanabe (2015) suggested that considering the rather inefficient growth
enhancement effect on sago palms, increased methane fluxes, and a possibility that
N application influences the generation of nitrous oxide, which is another
498
H. Ehara et al.