SAGO PALM 26-2: 29−36 (2019)

Nitrogen Uptake by Sago Palm (Metroxylon sagu Rottb.)
in Leyte of the Philippines
Masanori Okazaki1,*, Tomoe Nishi2, Toshihiko Momose2, Mitsuhisa Baba3,
Koki Toyota4, Malcelo A. Quevedo5 and Suzette B. Lina5
1
2

Japan Soil Research Institute Inc., 3-26-4, Yatocho, Nishitokyo, Tokyo 188-0001 Japan
Ishikawa Prefectural University, 1-308, Suematsu, Nonoichi, Ishikawa 921-8836 Japan3

4

Kitasato University, 35-1, Higashi 23 Ban, Towada, Aomori 034-8628 JapanTokyo University of Agriculture and Technology, 2-26-16, Nakacho, Koganei, Tokyo, 184-8588 Japan
5

Visayas State University, Baybay, Leyte, Philippines* Corresponding author

Abstract: Nitrogen uptake by sago palm with the application of nitrogen fertilizer (urea) with 15N-labeledammonium sulfate was studied in Leyte of the Philippines to estimate the effect of nitrogen fertilizers on sago
palm growth in the early to middle stages. The first application of nitrogen fertilizers for determining sampling
portions of leaflets was carried out at the early growth stage of sago in July of 2005, and the second nitrogen
application trial for determining nitrogen uptake was done in the middle growth stage in July of 2007, after
combining two 4 m x 2 m plots into one 4 m x 4 m plot. Since the nitrogen contents in the upper, middle, andbasal positions of leaflets were different from the sampling in February of 2006, the middle leaflet of the third
sago leaf was used for analysis. As the sago palm’s fertilizer use efficiency in the middle stage ranged from 10 to
20%, the use of nitrogen fertilizer for sago production should be limited.
Keywords: fertilizer use percent, 15N-labeled ammonium sulfate, nitrogen uptake, sago palm
Introduction

A long research history of nitrogen uptake by sago

palms had not shown effects of nitrogen fertilization.
Sago palms can grow in Entisols, Inceptisols, andHistosols of Southeast Asia (Okazaki and Sasaki,2017). No more fertile soils, however, are available inthe coastal area in which people are able to cultivate
sago palm. In the coastal areas of Malaysia andIndonesia, Histosols prevail, because of the smaller
amount of siltation through rivers shorter than thosewithin continents. Histosols are abundant in theirnatural conditions because of the difficulty of accessand crop production, so that researchers in Malaysia

and Indonesia have looked at Histosols in these areas.
Kueh (1979, 1980) started a sago field fertilizer

response experiment with a 9 m x 9 m square at the
Stapok Peat Research Station of Sarawak (Histosols,

Deep peat soil, Anderson III) in 1976. In 1979, heobserved that, in undrained deep peat, leaf productionin the third year appeared to indicate a depressing

effect of N (P<0.05), and that the leaf production ofleading palms showed no response to applications ofN, P, and K in the fourth year and beyond. However,
Kueh (1995) reported that the development speed ofleaf and nutrient components in leaves of sago palms

were affected by fertilization. Similarly, Paquay et al.
(1986) demonstrated the acceleration of leaf

development and leaf area increments due to theapplication of fertilizer to sago seedlings.
Furthermore, Kakuda et al. (2005) applied N, P, K,

Ca, Mg, Cu, Zn, Fe, and B to 5-year-old sago palms
in the thick peat soil of Riau, Indonesia, and obtained

data that the application of fertilizer increased the dry
matter weight of the petiole. On the other hand,
Purwanto et al. (2002) reportedly found no differencesin palm height, number of leaves, and leaf N content

M. Okazaki et al.

30

between the fertilized and unfertilized sago palms inwas started on Eutropepts in Pangasugan, Baybay,

had limited effects on the growth factors of sago

situated between the Eastern Visayas and Central

the fifth and twelfth months. The fertilization of slowrelease nitrogen fertilizers, Meister 40 and Meister 70,
palms in the Philippines (Kimura et al., 2007). Thesestudies indicated the limitation of nitrogen fertilization
experiments, because of high temperatures, precipitationof more than 2000 mm with dry and wet seasons, andpossible water-logged conditions due to irrigation.

The studies on nitrogen fertilization using a

15

N

tracer were performed by Lina et al. (2009), whoreported that sago palms responded to nitrogen

fertilizer in the early growth stage under greenhouse

Leyte, Philippines, in 2005. Pangasugan faces the

Camotes Sea within the Philippine archipelago and is
Visayas regions. Hamazaki et al. (2010) suggested

that Pangasugan was included in U2, with a dry

season in which the shortage of available water wasless than 30 days.

Soils were sampled in 2007 and 2008, being air-dried and sieved with a 2 mm mesh sieve for chemical
analysis and ground thoroughly with a mortar andpestle for total nitrogen and δ 15N analyses. The soil

was slightly acidic (pH 6.4) and 3.4 mS m-1 (Lina et al.,conditions, and nitrogen uptake from normal urea

2008). A sago palm field 50 m x 50 m (the 2005

few reports on sago palms’ utilization rate of nitrogen

was established. Extra control plots (without urea

fertilizer was 10-20% of the total nitrogen uptake bysago palms with immature root systems. There werefertilizer in field conditions with Inceptisols.
Especially, the application of nitrogen to sago palms
at the middle growth stage was limited.

The objective of this study was to clarify theutilization of nitrogen derived from urea fertilizer in
Inceptisols by sago palms using 15N tracers in Leyteof the Philippines.

1. Experimental field, soil, and urea application
with 15N-labeled ammonium sulfate

In an Af climate, with more than 2400 mm rainfall

per year with a maximum temperature of 33 to 35

throughout the year and precipitation of 100 mm in

April and 350 mm in December (Fig. 1), this study+(%"#%(#







 




 
%  ( '( - +% +$ +  ' * &, 

 

 


Fig 1. Climate
conditions
in Leyte,
Philippines Bar shows
 the monthly precipitation,
 
 and
 the polygonalline shows the maximum temperature.

sago palm growth was carried out continuously.

Experimental plots in 2007 were settled in three
replicates for each treatment: control (no application of
urea fertilizer) and urea (50 kgN/ha and 100 kgN/ha)with and without 15N-labeled ammonium sulfate.

Hence, three control plots, three urea 50 kgN/ha plots,

kgN/ha plots, and three 15N-labeled urea 100 kgN/haplots were prepared for the second fertilizer application
experiment. Urea fertilizer was applied approximately

10 cm around sago palms. Urea, a common fertilizer inSoutheast Asia for nitrogen application, is easilytransformed to ammonium nitrogen by urease in soil. It
is expected that ammonium nitrogen from ammonium
sulfate-tagged 15N and transformed from urea werelabeled ammonium sulfate in 2005 exhibited 3.35



 

The field was intermittently irrigated, and the study of

The first application of urea fertilizer with the 15N-



 

application) in 2005 were prepared for the second trial.

similarly absorbed by sago palms.







#"%&! another 4 m x 2 m plot into one 4 m x 4 m plot in 2007)

three urea 100 kgN/ha plots, three 15N-labeled urea 50

Materials and Methods

experimental plot of 4 m x 2 m was combined withatom %, which implied 15N-labeled ammonium sulfate(8436 ‰) (Lina et al., 2009). The 15N was applied at a

rate of 0.094 g per plot for 50 kgN/ha and 0.189 g perplot for 100 kgN/ha. Fertilization was performed within

0.562 m2 of the position. For the second trial, in 2007,

Nitrogen Uptake by Sago Palm (Metroxylon sagu Rottb.) in Leyte of the Philippines

31

urea fertilizer with 1.52 atom %, which implied 15N-

leaf dry weight, and x is the number of leaflets per

applied to the new plots, which were provided at 50

applied fertilizer nitrogen per palm (total fertilizer use

labeled ammonium sulfate (3202 ‰), was applied in thesame manner and depth as in the first trial. The 15N was
kgN/ha and 100 kgN/ha levels of common urea for the

first trial, at rates of 0.207 g per plot for 50 kgN/ha and0.416 g per plot for 100 kgN/ha, respectively. The

second application of N was performed in the former 4
15m x 2 m control plot of the first application, so that N
15

was added to the virgin soil plots. The 4 m x 4 m plot
should have one palm by felling one of the two. The

number of leaflets and leaf dry weight of 21 felledpalms (early trunk formation stage) in the control (noapplication of urea fertilizer) plots were determinedfrom October of 2007 to October of 2008 (Fig. 2).

Totalleafdryyweighhtkg

The total fertilizer nitrogen uptake of initiallypercent: TFUP) from October of 2007 to October of2008 was calculated as the product of the total weightof leaves and the difference between the N content in
the leaflets of the plot with and without fertilizer.
TFUP (%) = (TNleafletx – TNleaflet0) / TNfertx (total leaf dry weight per palm) x 100,(2)where TNleafletx is the total nitrogen content in leafletsat the urea application plot of 50 kgN/ha or 100

kgN/ha, TNleaflet0 is the total nitrogen content in leafletsat the plot without fertilizer application, and TNfert is

the initially applied total amount of fertilizer nitrogen.

14

The total leaf dry weight is obtained by the equation of

12

y = 0.0241 x - 6.77 (R2 = 0.905), where y is the total

10

leaf dry weight, and x is the number of leaflets per palm.

86yy=0.0241x–
6.67
R2 =0.905

42

2. Nitrogen in soil and sago leaflet samples

0
0

200

400

600

800

1000

Fig 2. Relationshipbetweenthe number  of leaflets

 and
 the

Numberofleaflets

total
weightleaf dry  of sago  palms measured in 2006
to 2008

The monthly fertilizer use percent (MFUP) of

nitrogen of initially applied fertilizer from October of2007 to October of 2008 was calculated using thefollowing equation:

MFUP (%) = (δ Nlab – δ Ncont) (TNleaflet) / (δ Nfert TNfert)
15

15

15

x (total leaf dry weight per palm) x 100,

(1)where δ Nlab is the N/ N ratio of the labeled palm,
15

15

14

δ Ncont is the N/ N ratio of the control palm, δ Nfert
15

palm (Fig. 2).

15

14

15

is the 15N/14N ratio of the fertilizer, TNleaflet is the total

nitrogen content in leaflets, and TN fert is the total

amount of fertilizer nitrogen initially applied. The

total leaf dry weight was obtained by the equation of

y = 0.0241 x - 6.77 (R2 = 0.905), where y is the total

Soil samples in the 4 m x 4 m plot were collectedfrom the experimental field in August of 2007 andJanuary of 2008, air-dried, sieved with a 2 mm meshsieve, and stored in a dark room. Soil analysis was
described in the previous report (Lina et al., 2008).

Since July of 2005, sago leaflet samples have beentaken from different positions of the sago leaf andupper, middle, and basal leaflets on the third leaf fromthe top, as Sim and Ahmed (1991) recommended thesampling of two leaflets from the middle portion of thethird leaf from the top on both sides of the rachis. Seven

months later, leaflet samples were taken from the third
leaf from the top of the standing sago palms every

month, because sago palms grow 10 leaves per year, on
average. The leaflets were cut and dried at 70 ° C for 4
hours in the Philippines.

3. Total nitrogen and δ 15N determination in soil
and sago leaflet samples

Leaflet samples were washed with deionized water,

M. Okazaki et al.

32oven-dried for 2 to 3 days at 70 ˚C

Table
Total nitrogencontent
and'!*'$%&δ 15N of soil (n$&+#= 3) in*+,.!$the study%field% (2.
'+%&$+)'"&'&+&+&$using a forced-draft oven, and groundwith a ball mill (Model MM 301,

N0

Retch, Haan, Germany) in Japan.

Total nitrogen

These samples were stored in a dark,cool room until analysis. Total



15
15
N‰
//N
‰

analyzer (PerkinElmer 2400, Waltham,
USA). The 15N was determined by ananalyzer(Euro-EA-

       
 
 
 

 !-3!07 Mean g/kg

SD

CV %

 

 

2007



Mean
SD
CV %


 
        !-3!07 Mean

SD

CV %

              

August       

15
N50:
N labeled urea, 50 kg/ha
! !   !  

application
15
N100:
N
labeled
urea,
100
kg/ha
!
       application

SD:Standard deviation, CV:Coefficient of variation

Milano, Italy) connected to acontinuous flow-isotope ratio mass
(IsoPrime,

Mean g/kg
SD
CV %

N100



Elemental Analyzer; EuroVector,
spectrometerAugust

nitrogen was analyzed with a CHNS/O
elemental

2007

N50

GV

Soil samples were taken from the surface of the experimental field.
.)+1!,/+%15%0%2!*%-&0.,2(%130&!#%.&2(%%6/%0),%-2!+8%+$    

Instruments, Manchester, UK). USGS-

40-2 (glutamic acid) was used as a second referencematerial (Lina et al., 2010). The values of δ N of
15

sago palm leaves ranged from 1.34 ± 1.64 ‰ in
Talau, Sarawak, Malaysia to 5.05 ± 0.61 ‰ in
Kendari, Sulawesi, Indonesia (unpublished).
Results

1. Total nitrogen content in soil and sago palm
samples

The mean height of sago palms in July of 2007 andJuly of 2008, shown in Table 1, are 269± 45 cm andTable 1. Mean height and number of living leaves ofsago palms

July of 2007

July of 2008

Mean palm height cm

269±45377±83

Mean number of living leaves

14±2

16±1

377± 83 cm (n = 15), and the mean number of living
leaves are 14 and 16, respectively.

The total nitrogen content and δ 15N values of soil

samples taken in August of 2007 (one month after
starting the second trial) and January of 2008 (6   

and 100 kgN/ha did not necessarily increase the total

nitrogen content. Meanwhile, the δ 15N values (N0) of

soil samples were 1.96 in August of 2007 and 2.53 in
January of 2008, which implies annual variation. The

application of urea remarkably increased the δ 15N

values in this study field. The increment of δ 15N values
did not always depend on the amount of urea applied.

The nitrogen contents of the different portions ofleaflets in Table 3 indicate the decreasing order ofTable 3. Total nitrogen content and δ 15N in differentof sago leaflets)&  portions
 $'* 

Total nitrogenSDCV %δ1515N‰
N‰
SD
CV %

g/kg

 

 



 

  
   

The sampling of sago leaflet (n = 3) was carried out in       Februaryof 2006.
 the third leaf
 from the apicalfrom was 
Leaflet sample
ofcollected.

SD: Standard
deviation CV: 
Coefficient of variation

upper, middle, and basal portions. However, the δ 15N

values with large coefficients of variation do not(1.97 gN/kg in August of 2007 and 2.12 gN/kg in

2. Nitrogen uptake by sago palms

sago fields (N0: control), Pangasugan, Leyte, was low

January of 2008). The urea application of 50 kgN/ha.02).-.&1!'.+%!9%2
//%0)$$+%!1!+
 

  
  
 
  
     

months after starting the second trial) are shown in

Table 2. The total nitrogen content in Eutropepts of

represent a trend within this study.

The relationship between the number of leafletsNitrogen Uptake by Sago Palm (Metroxylon sagu Rottb.) in Leyte of the Philippines

33

and the total leaf dry weight was obtained from 2006

kgN/ha application) and 3.3% (100kgN/ha),number of sago palm leaflets, and the monthly andthe third leaf. Since July of 2008 (10 months after urea

to 2008 (Fig. 2). Based on the equation from Fig. 2,

respectively, of the initial amount of nitrogen fertilizer,

the total leaf dry weight was estimated from thebased on the nitrogen content in the middle leaflet of

total fertilizer use percent of sago palms wereapplication), the nitrogen uptake from fertilizer by sago

calculated.

palms was obscure. The nitrogen supply as a fertilizer

The monthly total uptake of nitrogen per palm to

did not affect sago palm effectively.

fertilizer nitrogen (MFUP) initially applied with theurea application of 50 kgN/ha and 100kgN/ ha in 2007

3. Nitrogen uptake by sago palms from fertilizer

to 2008 is shown in Fig. 3. The nitrogen in sago palms

Figure 4 represents the total fertilizer use percent

on the control plot (without fertilizer) was derived from(TFUP) of sago palms at the middle stage with urea

the soil only. There were few differences in sago leaflet

fertilizer application of 50 kgN/ha and 100 kgN/ha.

MFUP%

50kgN/haapplication

100kgN/haapplication

100%
100

100%
100

95%

95%

90%

90%

85%

85%

80%

80%

75%
75

⣔ิ2
75%
75

⣔ิ2

70%

⣔ิ1
70%

⣔ิ1

65%

65%

60%

60%

55%

55%

50%
50

50%
50

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct

2007200820072008

Fig 3. Monthly fertilizerFig.3.Monthlyfertilizerusepercentinsagoleafletsofthethirdleafuse percent in sago leaflets of the third leaf from the top with the initial application of nitrogenffromthetopwiththeinitialapplicationofnitrogenth t
ith th i iti l
li ti
f it
Derivedfromfertilizer
D i dfDerivedfromsoil
il
MFUP:Monthlyfertilizerusepercent(%)

nitrogen content between the control

15

application (50 kgN/ha and 100 kgN/ha)plots, which suggests that the nitrogen

uptake of sago palms was from the soil,

not from fertilizer. Although from August

to December of 2007 the urea application

TFUP%%(without fertilizer) plot and nitrogen105

did not stimulate the nitrogen uptake ofsago palms, the MFUP increased until
March of 2008 and gradually decreased

with 50 kgN/ha and 100 kgN/haapplications. The MFUPs of sago palms,
with more- or less-developed root systems,

at the middle stage were, at most, 6.5% (500Fig
4. Total fertilizer use percent of sago palm with urea application
Fig.4.Totalfertilizerusepercentofsagopalmwithureaapplication(Oct.
2007 to Oct. 2008)(Oct.2007toOct.2008)
N50

N100

N50:Ureaapplicationof50kgN/ha
N100:Ureaapplicationof100kgN/ha
TFUP:Totalfertilizerusepercent(%)

M. Okazaki et al.

34

The TFUPs were 13.8% for 50 kgN/ha application

significant effect of N application on trunk height in1994) and wheat (Ishimaru et al., 2016).

fertilizer application had no significant positive effectand 11.5% for 100 kgN/ha application. These values

are relatively lower than those of rice (Kaneta et al.,Discussion

In this study, urea was used as a nitrogen fertilizer.

Urea is easily adsorbed on the soil surface with ahydrogen bond. Urease mediated ammonificationfrom urea, which caused the pH to increase slightly inlowland soils with the production of ammonium

carbonate. However, there was no significant

difference before and after urea fertilization(Kumazawa, 2000). The maximum activity ofammonification from urea was observed at 30 ° C, andall urea was changed to ammonium nitrogen within 2
to 3 days. The nitrification proceeded continuously
after ammonification, and the maximum nitrification

occurred at 27 to 29 ° C in soil with 24 to 27% watercontent. In the Philippines, Fillery et al. (1986)
reported that the loss of ammonia volatilization frompaddy fields where urea was applied, broadcast intofloodwaters 14 to 21 days after transplanting in

Munoz and Los Baflos, accounted for 45 and 60% ofthe15

N applied, respectively. In contrast, ammonia

volatilization in Vietnamese paddy rice fields, where
urea was applied at 20 to 40 kgN/ha as a split

application for a total of 80 to 100 kgN/ha throughout

thirteen years of growth (Kueh, 1989, 1990, 1995).
Similarly, Jaman (1983) found in Sarawak that NPK

on the rate of leaf production of sago palms in the firstyear at the Sungai Talau Peat Research Station. Jaman(1984, 1985) reported that NPK fertilizer application,pruning, weeding, seed germination, spacing, andintercropping had no significant positive effect on theannual leaf production rate of sago palms. Kakuda etal. (2005) also reported that applying seven times theusual amount of N, P, K, Ca, Mg, Cu, Zn, Fe, and B
to Histosols provided a significant difference inpetiole and sucker dry weight and that any difference
was not found in other growth factors of sago palms.

Our results on nitrogen uptake from urea fertilizer in
Inceptisols indicate a limitation of up to 13%, whichindicates that nitrogen fertilizer has a small effect on
growth and final starch production.

The small effect of nitrogen (N) application on sago

palm growth is explained by the findings of theendophytes’ activities on the N fixation (Shrestha et al.,2006, 2007). When sago palm becomes easily able toabsorb N from the soil, it does not require N support byendophytes. Accordingly, it is concluded that
endophytes play an important role in sago palm growth

without N application. Another explanation is theemission of nitrous oxide (N2O) and nitric oxide (NO)the cropping period, was 1.7 to 14.6% of the applied

production through nitrification and denitrification in

importance to nitrification/denitrification in tropicalaccompanied with the dissolution and elution of

N (Watanabe et al., 2009). Ammonia volatilization is

the important nitrogen loss mechanism and has equal
wetlands.

There has been a long time to discuss the effect ofboth reductive and oxidative conditions of sago fields

intermittently after applying urea fertilizer,
nitrogen by irrigation water. The production of nitrous
oxide (N 2O) and nitric oxide (NO) (Firestone andnitrogen application to sago palms in Sarawak ofDavidson, 1989) easily occurs in sago fields

application on leaf production in undrained Fibrists atthat N2O and NO emissions were observed in a Typic

Malaysia. Since 1976, Kueh (1979, 1980, 1981, 1982,

1983) found no effect of nitrogen (ammonium sulfate)

Stapok of Sarawak. In case of the eleventh year of
growth, trunk heights in Histosols with minimal

drainage at Stapok Station seemed to increase with N
application (Kueh, 1987). However, there was nointermittently irrigated by irrigation water in Histosols(Inubushi et al., 2003). Lan et al. (2014) represented
Epiaquept in US Soil Taxonomy with paddy ricecultivation. Sago palm fields also have the repetition ofoxidative and reductive conditions seasonally, in asituation similar to that of the paddy field.

Nitrogen Uptake by Sago Palm (Metroxylon sagu Rottb.) in Leyte of the Philippines

References

Fillery, I. R. O., J. R. Simpson and S. K. De Datta
1986 Contribution of ammonia volatilization to35

Soil characteristics in sago palm grown area;

Factors associated with fate of inorganic nitrogenin soil. Sago Palm 8: 9-16. (in Japanese)

total nitrogen loss after applications of urea to

Kakuda, K., A. Watanabe, H. Ando and F. S. Jong

Microbiological basis of NO and N2O production(Metroxylon sagu Rottb.) cultivated in peat soil.

wetland rice fields. Fertilizer Research 8: 193-202.

Firestone, M. K. and E. A. Davidson 1989

and consumption in soil. In: Exchange of Trace

Gasses between Terrestrial Ecosystems and the2005 Effects of fertilizer application on the root

and aboveground biomass of sago palm
Japanese Journal of Tropical Agriculture 49: 264269.

Atmosphere. (Andreac, M. O. and D. S. Schimel

Kaneta, Y., H. Awasaki and Y. Murai 1994 The non-latest research works in pedology in AsianJapanese Journal of Soil Science and Plant

eds.) John Wiley & Sons (New York) 7-21.

Hamazaki, T., T. Ohkura and K. Miura 2010 The
countries 4, The latest studies on the Philippine

tillage rice culture by single application of fertilizer

in a nursery box with controlled-release fertilizer.
Nutrition 65: 385-391. (in Japanese)

soils, Soil environment and agriculture in the

Kimura, S. D., M. Okazaki, S. B. Lina and M. Igura

Inubushi, K., Y. Furukawa, A. Hadi, E. Purnomo andPangasugan, Leyte, pp. 92, Tokyo University oftropical islands. Japanese Journal of Soil Scienceand Plant Nutrition 81: 267-272. (in Japanese)

H. Tsuruta 2003 Seasonal changes of CO2, CH4
and N2O fluxes in relation to land-use change intropical peatlands located in coastal area of South
Kalimantan. Chemosphere 52: 603-608.

Ishimaru, T., T. Arai and T. Yamamoto 2016
Fertilizer nitrogen utilization rate and contribution

ratio of nitrogen from soil in the grain protein
content of the wheat cultivar “ChikushiW2” forChinese noodles. Japanese Journal of Crop Science85: 385-390. (in Japanese)

Jaman, O. 1983 Fertilizer response in drained peat at
Sungai Talau Station. Annual Report of
Department of Agriculture of Sarawak, p. 87–88,
Department of Agriculture of Sarawak.

Jaman, O. 1984 Fertilizer response in drained peat at
Sungai Talau Station. Annual Report of
Department of Agriculture of Sarawak, p. 97-101,
Department of Agriculture of Sarawak.

Jaman, O. 1985 Fertilizer response in drained peat at
Sungai Talau Station. Annual Report of

Department of Agriculture of Sarawak, p. 105-110,
Department of Agriculture of Sarawak.

Kakuda, K. H. Ando, Y. Yoshida, Y. Yamamoto, Y.

Nitta, H. Ehara, Y. Goto and B. H. Puruwanto 2000

2007 Sago project in Leyte, Sago starch productionin the sago – taro intercropping system inAgriculture and Technology.

Kueh, H. S. 1979 Sago NPK fertilizer experiment.

Annual Report of Department of Agriculture of

Sarawak, p. 157-158, Department of Agriculture of
Sarawak.

Kueh, H. S. 1980 Sago NPK fertilizer experiment.

Annual Report of Department of Agriculture of

Sarawak, p. 167-168, Department of Agriculture of
Sarawak.

Kueh, H. S. 1981 Sago NPK fertilizer experiment.

Annual Report of Department of Agriculture of

Sarawak, p. 169-170, Department of Agriculture of
Sarawak.

Kueh, H. S. 1982 Sago NPK fertilizer experiment.

Annual Report of Department of Agriculture of

Sarawak, p. 168-170, Department of Agriculture of
Sarawak.

Kueh, H. S. 1983 Fertilizer response in undrained

deep peat at Stapok Station. Annual Report of
Department of Agriculture of Sarawak, p. 85-86,
Department of Agriculture of Sarawak.

Kueh, H. S. 1987 Fertilizer response of sago in deep
peat under minimal drainage conditions at Stapok

Station. Annual Report of Department of36

M. Okazaki et al.

Agriculture of Sarawak, p. 81, Department ofContributions to Food Security and Sustainablepeat under minimal drainage conditions at Stapok

Paquay, L. E. C. R., D. L. Schuiling, G. H. De

Agriculture of Sarawak.

Kueh, H. S. 1989 Fertilizer response of sago in deep
Station. Annual Report of Department ofAgriculture of Sarawak, p. 86-87, Department ofAgriculture of Sarawak.

Kueh, H. S. 1990 Fertilizer response of sago in deep
peat under minimal drainage conditions at Stapok

Livelihoods (H. Ehara, Y. Toyoda, D. V. Johnsoneds.) Springer Open (Singapore) 193-206.

Buruijin, R. W. P. Roos and M. Flach 1986 Effectsof nutrient shortage on young sago palm seedlings.
In Sago-’85: Proceedings of the 3rd International

Sago symposium. (ed.) Yamada, N. and K.
Kainuma, Tokyo, p. 1-6

Station. Annual Report of Department of

Purwanto, B. H., K. Kakuda, H. Ando, F. S. Jong, Y.

Kueh, H. S. 1995 The effects of soil applied NPK(Metroxylon sagu Rottb.) to controlled release N

Agriculture of Sarawak, p. 68-69, Department ofAgriculture of Sarawak.

fertilizers on the growth of the sago palm (Metroxylon
sagu Rottb.) on undrained deep peat. In: Proceedings

Yamamoto, A. Watanabe and T. Yoshida 2002
Nutrient availability and response of sago palm

fertilizer on coastal lowland peat in the tropics. Soil
Science and Plant Nutrition 48: 529-537.

of the fifth International Sago Symposium, 1994, Hat

Shrestha, A., K. Toyota, T. Nakano, M. Okazaki, M.

Kumazawa, K. 2000 Urea and fertilizer and Mitsui’s

parts of sago palm (Metroxylon sagu) and

Yai, (Subhadrabandhu, S. and S. Sdoodee eds. Acta
Horticulture 389) ISHS (Leiden) 67-76.

Laboratory. Fertilizer Science 22: 35-60. (inJapanese)Lan, T., Y. Han, M. Roelcke, R. Nieder, Z. Cai 2014

Sources of nitrous and nitric oxides in paddy soils:

Nitrification and denitrification. Journal ofEnvironmental Sciences 26: 581–592.

Lina, S., M. Okazaki, S. D. Kimura, S. Matsumura,
M. Igura, M. A. Quevedo, A. B. Loreto and A. M.
Mariscal 2008 Ammonium nitrogen releasing from

A. Quevedo, A. B. Lotreto, A. A. Mariscal andAbayon, E. 2006 Nitrogen-fixing activity in various
characterization of aerobic nitrogen-fixing bacteriacolonizing the sago palm. Sago Palm 14: 20-32.

Shrestha, A., K. Toyota, M. Okazaki, Y. Suga, M. A.
Quevedo, A. B. Loreto and A. A. Mariscal 2007

Enhancement of nitrogen-fixing activity ofEnterobacteriaceae strains isolated from sago palm(Meteroxylon sagu) by microbial interaction with
non-nitrogen fixers. Microbes and Environments
22: 59-70.

kaolin-dominant soil in Leyte of the Philippines.

Sim, E-S and M. I. Ahmed 1991 leaf nutrient

Yonebayashi, M. Igura, M. A. Quevedo and A. B.

Proceedings of the fourth International Sago

Pedologist 52: 107-117.

Lina S. B., M. Okazaki, S.D. Kimura, Y. Yano, K.
Loreto 2009 Nitrogen uptake by sago palm(Metroxylon sagu Rottb.) at early stage of growth.
Soil Science and Plant Nutrition 55: 114-123.

Lina, S. B., M. Okazaki, S. D. Kimura, S. Yano, K.

Yonebayashi, S. Matsumura, M. A. Quevedo and A.

variations in sago palms. In: Towards greater
advancement of the sago industry in the ‘90s,

Symposium, August 6-9, 1990, Kuching, Malaysia(Ng, T.-T., Y.-L. Tie and H.-S. Kueh eds.) Ministryof Agriculture & Community Development,
Sarawak and Department of Agriculture, Sarawak,
Malaysia (Kuching) 94-102.

B. Loreto 2010 Nitrogen uptake and growth response

Watanabe, T., T. T. Son, N. N. Hung, N. Van Truong,Okazaki, M. and Y. Sasaki 2017 Soil environment inflooded paddy fields in Vietnam. Soil Science andof sago palm (Metroxylon sagu Rottb.) to various
forms of urea fertilizer. Sago Palm 18: 73-83.

sago palm forest. In: Sago Palm, Multiple

T. Q. Giau, K. Hayashi and O. Ito 2009
Measurement of ammonia volatilization fromPlant Nutrition 55: 793-799.