Kagoshima University Research Center for the Pacific Islands Occasional Papers No.39, 99-105, 2003
Section 3, Report 3. The Progress Report of the 2000 and 2001 Survey of the Research Project“Social Homeostasis of Small Islands in an Island-zone”

99

PRELIMINARY REPORT ON SOIL CONDITIONS IN YAP ISLAND AND
ULITHI ATOLL OF THE FSM
TOMINAGA Shigeto ＊1), ICHITANI Katsuyuki1) , ONJO Michio1), TSUDA Katsuo 1),
PARK Byoung-Jae2), NAGAYAMA Hiroshi1), KAMADA Noriyuki 1) , and
KOHNO Rumiko 1)

Abstract
Seventy-one soil samples were collected from upland soils of Yap and four inhabited islands ofUlithi Atoll (Mogmog, Falalop, Asor, Fassarai Islands) of Yap State which were planted to taro, coconut palm and citrus trees. Chemical properties of the soil samples collected were examined and differences in the soils from the various islands were determined.
The soil samples collected from the four islands of Ulithi Atoll were alkaline since the soil pH
was greater than 8.1. The soil samples collected on Yap were neutral (average pH=7.0). These differences were due to the method by which the islands were formed. Ulithi Atoll was formed by theupheaving of coral from a reef while Yap was formed by a volcanic eruption. The soil exchange
capacity (EC) was higher in soils of the Ulithi Atoll islands than in those of Yap Island. The water content was very high in soils of taro patches while the soil water content was low in soils in which citrus
and coconuts were growing. There were no clear differences in soil nitrogen, phosphate, potassium,
calcium and magnesium among the samples collected on all the islands. The nitrogen, phosphate andpotassium levels were low while calcium and magnesium content was high in all soil samples collected.
Keywords: chemical property, EC, pH, soil, water content

Introduction
The agricultural productivity of Yap State of the Federated States of Micronesia (FSM) is
low. Taro, coconut, banana, and a few other tropical crops are the main crops grown on Yap
Island and the four inhabited islands in Ulithi Atoll of Yap State.
The low yields of all crops grown in Yap State can be accredited to several factors, including geographic location, climatic conditions, and etc., but soil conditions could play a major rolein the low yields obtained. Crops grow well and produce high yields on soils of good texture andchemical content, therefore an investigation of soil properties is needed to determine the rolesoils play in the low yields received in Yap State. In order to establish the physical and chemical
property status of the soils of Yap State, 71 soil samples were collected from upland soils of Yap
and the four inhibited islands of the Ulithi Atoll that were planted to taro, coconut palm andcitrus. The soil properties of the samples collected were compared.

＊)

Author for correspondence. Fax +81 992858552, e-mail tominaga@agri.kagoshima-u.ac.jp
Faulty of Agriculture, Kagoshima University. Kagoshima 890-0065, Japan.
2)
United Graduate School of Agriculture Sciences, Kagoshima University. Kagoshima 890-0065, Japan1)

100 T OMINAGA Shigeto, ICHITANI Katsuyuki, ONJO Michio, T SUDA Katsuo, PARK Byoung-Jae, NAGAYAMA Hiroshi, KAMADA Noriyuki, and KOHNO RumikoMaterials and Methods
A total of 71 soil samples were collected from Yap and the four inhabited islands (Mogmog,
Falalop, Asor, and Fassarai) of the Ulithi Atoll. Of the 71 samples, 27 samples were collectedon Yap Island, 12 were collected on Mogmog, 12 on Falalop, 8 on Asor and 12 samples werecollected on Fassarai Island. A sampling plot of each island is shown in Fig. 1. Soil samples wereobtained by digging to a 20 cm depth after determining the north latitude and longitude of eachsampling position. The collected soil samples were brought to Kagoshima University under refrigeration. In a Kagoshima University laboratory, the principal chemical characteristics of thesamples (pH, EC, water content, nitrogen (N), phosphate (P 2 O 5 ), potassium (K 2 O), calcium

Fig.1 Locations of soil sampling plots

101(CaO) and Magnesium (MgO)) were determined. The chemical determinations were conductedusing standard laboratory methods and nitrogen, phosphate, potassium, calcium and magnesium
analysis were calculated to percent or mg per soil dry weight.

Results and Discussion
Yap Island
The pH value of 27 soil samples (20 citrus plantings, 6 taro patches and 1 other) that werecollected on Yap Island showed high coefficients of variation (C.V.) for soil pH that ranged from
pH=4.7 to pH=8.8 with an average pH of 7.0. Thirteen of the 27 soil samples from Yap Island
were alkaline with a pH greater than 7.5. Eight of the soil samples collected from Yap Island
were acid with a pH of 6.5 or less while others were neutral in pH (pH=6.6 to 7.4). The exchange
capacity (EC) was low in all soils sampled with an average EC value of 0.061. Twenty-one of
the 27 soils had very low EC values that were less than 0.100. The soil water content of the samples collected on Yap Island varied between 8.8 and 85.5% with an average soil water content
of 25.6%. The soil water content of soil samples taken from taro patches varied between 33.1
and 85.5% while the water content of soil samples taken from citrus plantings ranged between
8.8 and 31.3%. The nitrogen content of the soils sampled on Yap Island varied between 0.12 and1.16% with an average nitrogen content of 0.40%. Phosphate content of the same samples varied
between 0.53 and 6.32 mg/100g soil and the mean phosphate value was 2.42 mg/100g of soil.
Twenty-four of 27 soil samples contained 3.01 mg of potassium per 100g of soil. Soil calcium
content varied between 13.99 and 391.72 mg of calcium per 100g of soil with a mean value of
136.14 mg/100g of soil. Magnesium content varied between 8.95 and 117.72 mg/100g with amean soil calcium value of 4.01 mg/100g of soil (Table 1).
Mogmog Island
The pH value of 12 soil samples (6 from citrus plantings, 5 from taro patches and 1 froma coconut planting) collected on Mogmog Island in Ulithi Atoll had a low C.V., were alkaline,
and the pH values ranged from 7.5 to 8.6. The mean EC value of the soils sampled on Mogmog
Island was 0.157 and the range in EC value was between 0.075 and 0.361. The pH and the EC
values of soils sampled on Mogmog Island tended to be higher than those of Yap Island. The
water content was highest in soils sampled from taro patches and was lowest in soils sampled in
citrus plantings. The average, minimum and maximum nitrogen levels in the soils sampled were0.97, 0.17 and 2.15%, respectively. The nitrogen content in soils obtained from taro patchestended to be higher than in samples taken from plots in which coconut or citrus was growing.
Phosphate content of soil samples taken from Mogmog Island was much higher than those of
Yap Island. The average, minimum and maximum values were 21.63, 0.58, and 183.50 mg/100g,
respectively. The average value for potassium content of the Mogmog soil samples was 14.06
mg/100g of soil but eight of twelve soils showed a similar potassium content of 3.01 mg/100g
of soil. The calcium content of the soils sampled on Mogmog Island was lower than those of Yap
Island and the average, minimum and maximum calcium values of the Mogmog soil samples
were 31.62, 2.80 and 75.55 mg/100g of soil, respectively. The magnesium content of the soils
sampled on Mogmog Island was higher than those collected from Yap Island. Soil magnesium
levels of the soils sampled on Mogmog Island were similar to the soil magnesium levels of soil
samples taken from the other Ulithi Islands with an average soil magnesium content of around
100 mg/100g (Table 2).

102 T OMINAGA Shigeto, ICHITANI Katsuyuki, ONJO Michio, T SUDA Katsuo, PARK Byoung-Jae, NAGAYAMA Hiroshi, KAMADA Noriyuki, and KOHNO Rumiko

Falalop Island
Twelve soil samples were collected from Falalop Island (8 from citrus plantings, 2 fromtaro patches, and 2 from coconut plantings). All soils sampled on Falalop were highly alkaline
and the soil pH of all soils sampled on Falalop was greater than 8.1 with a mean pH value of 8.4.
The mean C.V. for the pH values of the soils sampled on Falalop was 3.0. The pH of soils on
Falalop Island were higher than that of the soil samples collected on Yap Island. The EC valueof the soil samples collected from Falalop Island was 0.126 and minimum and maximum EC values were 0.053 and 0.206, respectively. The average, minimum and maximum soil water contents were 19.0, 3.9 and 48.7%, respectively. The water content of taro patch soils was as highin soil samples collected from taro patches on Falalop Island as they were in taro patches sampled on the other islands. The nitrogen content of the soils sampled on Falalop Island was thelowest of all the soils sampled on the islands of the Ulithi Atoll, although the soil nitrogen content from Falalop Island soil samples was higher than that of the soils sampled on Yap Island.
The average, minimum, and maximum soil nitrogen values for soils sampled on Falalop Island
Table 1. Chemical properties of upland soil collected on Yap Island of the FSM
Location
North
Crop
LongitudepHNo.
latitude1
Citrus 9.26.30 138.04.00 7.02
Taro
9.26.30 138.04.00 7.1
3
Citrus 9.26.19 138.03.51 8.3
4
Citrus 9.26.19 138.03.51 7.5
5
Citrus 9.30.56 138.04.49 7.96Taro
9.30.56 138.04.49 8.7
7
Citrus 9.30.43 138.05.34 7.1
8
Citrus 9.31.31 138.09.14 8.0
9Citrus 9.31.36 138.10.09 6.4
10
Citrus 9.31.43 138.10.07 6.9
11
Citrus 9.31.20 138.10.57 7.5
12
Citrus 9.31.20 138.10.57 8.5
13
Citrus 9.36.36 138.10.27 8.3
14
Citrus 9.28.17 138.04.23 8.4
15
Citrus 9.28.35 138.04.27 4.7
16
Citrus 9.30.36 138.06.46 7.8
17
Citrus 9.36.04 138.10.37 7.0
18Taro
9.36.04 138.10.37 5.3
19Taro
9.36.06 138.10.38 6.3
20
Taro
9.36.06 138.10.38 5.6
21
Citrus 9.36.08 138.10.43 8.3
22
Citrus 9.36.04 138.10.49 8.8
23Taro
9.32.01 138.10.00 4.7
24
Citrus 9.31.53 138.10.08 5.925
Citrus 9.31.52 138.10.13 6.9
26
Citrus 9.31.48 138.10.15 6.527
Garden 9.32.01 138.10.22 7.8
Average
7.0
C.V.
17.6

Water
N
content (%)
0.062
25.4
0.21
0.063
33.1
0.17
0.135
19.4
0.38
0.107
13.9
0.30
0.022
21.7
0.20
0.011
35.4
0.12
0.035
23.2
0.30
0.022
28.7
0.22
0.014
15.5
0.96
0.067
19.5
1.04
0.032
22.9
0.22
0.113
17.4
0.14
0.096
9.5
0.58
0.101
8.8
0.17
0.043
15.9
0.32
0.085
20.7
0.34
0.060
21.8
0.28
0.068
58.7
0.26
0.031
35.9
0.17
0.026
46.4
0.32
0.117
15.7
0.41
0.085
9.2
0.19
0.036
85.5
0.93
0.022
31.3
0.41
0.049
21.1
0.37
0.034
20.0
0.53
0.113
14.9
1.16
0.061
25.6
0.40
60.03964.3 73.35
EC

P2O5

K2O
CaO MgO(mg/100g・dw)
2.27
3.01 263.01 49.91
1.84
3.01 324.57 35.98
1.28
3.01 13.99 92.52
0.53
3.01 16.76 75.11
2.21
3.01 114.72 107.60
0.99
3.01 156.69 68.65
1.11
3.01 142.70 75.77
0.64
3.01 64.35 30.51
0.73
3.01 198.66 25.04
0.58
3.01 64.56 85.39
1.54
3.01 151.09 83.07
1.02
3.01 53.16 56.87
5.49
3.01 72.75 102.63
3.45
3.01
121.37
3.61
3.01 131.51
8.95
6.32
3.01 36.37 98.98
2.82
3.01 58.76 117.72
2.14
3.01 176.27 73.12
3.09
3.01 22.38 78.59
1.14
3.01 95.13 103.63
4.37
3.01 25.18 96.00
5.11
6.03 391.72 98.15
0.94
3.01 148.29 61.35
2.59
3.01 139.90 85.06
2.82 15.06 268.61 44.10
4.68
9.04 237.83 50.73
1.95
6.03 170.68 73.62
2.42
3.91 136.14 74.02
67.16 67.04 72.87 39.18

PRELIMINARY REPORT ON SOIL CONDITIONS IN YAP ISLAND AND ULITHI ATOLL OF THE FSM 103

were 0.49, 0.22 and 0.85%, respectively. Phosphate content of the soils sampled on Falalop
Island was the lowest of the four islands of Ulithi Atoll and varied between 0.78 and 20.37
mg/100g of soil. The average soil phosphorous content was 4.21 mg/100g. Soil potassium levelsof the soils sampled on Falalop Island were similar to the soil potassium levels of soil samples
taken from Yap Island and Asor Island, but the potassium level of Falalop soils was lower thanthose of Mogmog Island and Fassarai Island. The calcium content of the Falalop Island soil samples were the highest of any soil sampled on the Ulithi Atoll but lower than that of Yap Island.
The soil calcium minimum and maximum values for the Falalop Island soils was 2.80 to 492.45
mg/100g of soil. The soil magnesium content of Falalop Island soils was the lowest of all soils
sampled from the Ulithi Atoll Islands but higher than that of Yap Island (Table 3).
Table 2. Chemical properties of upland soil collected on Mogmog Island in Ulithi Atoll of the FSM
Location
North
Crop
LongitudeNo.
latitude1
Citrus 10.04.58 139.42.42
2
Taro
10.04.58 139.42.42
3
Taro
10.05.00 139.42.41
4
Taro
10.05.00 139.42.41
5
Citrus 10.04.59 139.42.36
6
Citrus 10.04.55 139.42.29
7
Citrus 10.04.56 139.42.39
8
Taro
10.04.59 139.42.39
9
Taro
10.05.01 139.42.38
10Citrus11
Citrus12
Coconut
Average
C.V.
-

pH
8.0
7.9
7.6
7.5
8.4
8.6
8.4
7.7
8.1
8.5
7.9
8.6
8.1
5.1

Water
N
P2O5
K2O
CaO MgO
content (%)(mg/100g・dw)
0.091
11.4
0.43
1.20
3.01 75.55 93.01
0.307
89.1
2.07 183.50 45.19 16.79 108.43
0.361
79.6
2.03
5.94 84.35 11.19 104.45
0.208
78.7
1.84
5.71
9.04 11.19 107.77
0.065
12.3
0.36
2.35
3.01 44.77 102.80
0.124
15.1
0.72
2.29
3.01
103.63
0.081
8.8
0.42
7.75
3.01
8.39 106.11
0.180
81.0
2.15 23.44
6.03 44.77 102.80
0.200
34.2
0.66
3.82
3.01 47.57 100.81
0.117
16.6
0.35
4.57
3.01 53.16 95.83
0.075
15.7
0.41 18.36
3.01
2.80 100.14
0.078
7.4
0.17
0.58
3.01
107.270.157
34.5
0.97 21.63 14.06 31.62 102.76
61.64989.9 82.02 237.93 179.13 77.60
4.60
EC

Table 3. Chemical properties of upland soil collected on Falalop Island in Ulithi Atoll of the FSM
Location
North
Crop
LongitudeNo.
latitude1
Citrus 10.00.55 139.47.20
2
Citrus 10.00.39 139.47.25
3
Citrus 10.00.39 139.47.25
4Citrus 10.00.32 139.47.32
5
Taro
10.00.56 139.47.30
6
Coconut 10.00.56 139.47.30
7
Taro
10.00.50 139.47.28
8Citrus 10.00.46 139.47.27
9Citrus 10.00.46 139.47.27
10
Citrus 10.00.46 139.47.27
11
Citrus 10.00.39 139.47.32
12
Coconut 10.00.42 139.47.45
Average
C.V.
-

pH
8.7
8.7
8.4
8.3
8.3
8.2
8.2
8.1
8.3
8.4
8.6
8.9
8.4
3.0

Water
N
P2O5
K2O
CaO MgO
content (%)(mg/100g・dw)
0.071
10.6
0.35
3.63
3.01
103.63
0.053
7.8
0.22
1.12
3.01 41.97 106.78
0.097
12.4
0.38
4.06
3.01
2.80 87.05
0.148
14.3
0.85
1.88
6.03
104.95
0.142
26.9
0.51
0.78
3.01
101.300.192
43.0
0.54 11.33
3.01 492.45 106.28
0.176
48.7
0.67
2.23
3.01 55.96 87.71
0.206
3.9
0.52
1.07
6.03
106.780.132
14.8
0.76 20.37
3.01
97.66
0.084
11.6
0.29
1.93
3.01 47.57 102.80
0.089
15.8
0.45
0.88
3.01
2.80 77.26
0.117
18.2
0.40
1.20
3.01
84.72
0.126
19.0
0.49
4.21
3.52 107.26 97.24
39.10872.6 38.14 139.36 33.36 177.22 10.57
EC104 T OMINAGA Shigeto, ICHITANI Katsuyuki, ONJO Michio, T SUDA Katsuo, PARK Byoung-Jae, NAGAYAMA Hiroshi, KAMADA Noriyuki, and KOHNO RumikoAsor Island
The Asor Island soils, as was the case with the other Ulithi Island soils, were alkaline. The
average pH was 8.2 with a 7.9 minimum pH and an 8.5 maximum pH. The average, minimum
and maximum EC were 0.152, 0.068 and 0.294, respectively. The soil water content was high intaro patch soils (43.0 to 86.8%) while the soil water content of soils of citrus and coconut plantings was much lower (7.1 to 16.3%). The average soil nitrogen content was 0.92%, but 2 of thetaro patch soils sampled had soil nitrogen levels greater than 2%. Soil phosphate content in one
soil sample from a citrus grove was high (i.e. 11.64 mg/100g of soil). However, the remaining
7 citrus soils had low phosphate levels (less than 1.48 mg/100g). The phosphate content of thesamples taken from the taro patches varied between 0.82 and 12.51 mg/100g. All soil samples
from Asor Island showed similar potassium content in the range of 3.01 mg/100g. However, thecalcium content fluctuated widely depending on sampling points. The average, minimum andmaximum calcium values were 79.04, 2.08 and 170.68 mg/100g, respectively. The average soil
magnesium content of Asor Island soils was 102.03 mg/100g, but the soil magnesium content did
not fluctuate greatly among the sampling points (Table 4).
Table 4. Chemical properties of upland soil collected on Asor Island in Ulithi Atoll of the FSM
Location
North
Crop
LongitudeNo.
latitude1
Citrus 10.01.28 139.46.03
2
Citrus 10.01.28 139.46.04
3
Taro
10.01.28 139.46.02
4
Taro
10.01.33 139.46.00
5
Taro
10.01.33 139.46.00
6
Taro
10.01.31 139.45.58
7
Citrus 10.01.24 139.46.01
8
Coconut 10.01.22 139.46.05
Average
C.V.
-

pH
8.4
8.4
7.9
7.9
8.1
8.0
8.5
8.4
8.2
3.1

Water
N
P2O5
K2O
CaO MgO
content (%)(mg/100g・dw)
0.082
14.8
0.50
1.48
3.01
86.38
0.093
16.3
0.38
0.78
3.01 81.14 96.83
0.189
86.8
2.16 12.51
3.01 61.56 113.41
0.294
67.2
0.97
2.49
3.01
105.12
0.252
43.0
0.47
0.82
3.01
102.13
0.142
80.8
2.32
8.16
3.01
2.80 110.42
0.068
7.1
0.21 11.64
3.01 170.68 93.68
0.095
11.6
0.33
1.28
3.01
108.27
0.152
40.9
0.92
4.87
3.01 79.04 102.03
55.94180.9 92.41 104.09
0.00 88.02
9.00
ECFassarai Island
As was the case with soils of the other Ulithi Islands, Fassarai Island soils were alkaline.
The average, minimum and maximum pH values were 8.1, 7.7 and 8.8, respectively. The average, minimum and maximum EC of Fassarai Island soils was the highest of all soils sampled on
the four Islands of the Ulithi Atoll and had a average EC value of 0.162. Soil water content of
the taro patches sampled also fluctuated greatly. Minimum and maximum water content in soilsof the taro patches was 22.0 and 84.0%, respectively. As was the case with other island soils, thesoil water content of soils in which citrus was growing was low compared to the taro patches.
The nitrogen level of Fassarai Island soils was similar to that of the other islands of the Ulithi
Atoll. The average, minimum and maximum soil nitrogen content of Fassarai Island soils was
0.81, 0.29 and 1.97%, respectively. The phosphate content of Fassarai Island soils was the highest of all soils sampled from the 4 islands of the Ulithi Atoll and Yap Island. The average soil
phosphorous content was 31.66 mg/100mg. The potassium content of Fassarai Island soils was
lower than that of Mogmog soils but higher than those of Yap, Falalop and Asor Islands. The average soil potassium content sampled from Fassarai Island was 9.04 mg/100g. The mean calcium
content of soils sampled on Fassarai Island was the lowest of the 4 islands of Ulithi Atoll andPRELIMINARY REPORT ON SOIL CONDITIONS IN YAP ISLAND AND ULITHI ATOLL OF THE FSM 105

Yap Island. Soil calcium in Fassarai Island soils was measured at 21.45 mg/100g of soil. The average, minimum and maximum magnesium values obtained for Fassarai Island soils was 98.09,
89.03 and 108.10 mg/100g, respectively (Table 5).
Table 5. Chemical properties of upland soil collected on Fassarai Island in Ulithi Atoll of the FSM
Location
No.
1
2
3
4
5
6
7
8
9
10
11
12
Average
C.V.

Crop
CitrusCitrusTaro
Taro
CitrusTaro
Taro
Citrus
Field
Taro
Taro
Citrus-North
Longitude
latitude9.53.59 139.39.33
9.53.59 139.39.33
9.53.59 139.39.33
9.53.59 139.39.33
9.53.59 139.39.35
9.53.59 139.39.35
9.53.59 139.39.35
9.54.01 139.39.33
9.54.38 139.40.01
9.54.58 139.40.01
9.54.40 139.40.02
9.53.50 139.39.34
-

pH
8.4
8.2
7.7
7.6
8.7
7.7
7.7
8.4
8.8
8.1
8.2
8.2
8.1
4.9

Water
N
P2O5
K2O
CaO MgO
content (%)(mg/100g・dw)
0.098 13.4
0.57 29.58 9.04 36.37 94.17
0.106 14.5
0.43 14.85 0.00 30.78 101.80
0.229
0.173 84.0
1.97 64.84 0.00
0.00 108.10
0.081
9.4
0.29
3.33 6.03 19.59 102.96
0.213
0.239 82.6
1.93 169.50 48.20 25.18 99.15
0.106 12.5
0.50 16.84 6.03 53.16 91.19
0.075 13.4
0.40
2.19 3.01
5.60 103.96
0.377 41.4
0.55
2.93 6.03
100.970.112 22.0
0.72
5.57 6.03 13.99 89.53
0.134 16.0
0.77
6.94 6.03
8.39 89.03
0.162 30.9
0.81 31.66 9.04 21.45 98.09
54.972 93.9 75.62 164.46 155.56 78.53
6.80
EC

Conclusions
Some chemical properties of upland soils of Yap and 4 inhabited islands of Ulithi Atoll
were compared. Soils of the 4 islands of the Ulithi Atoll were alkaline with an average soil pH
greater than 8.1. Yap Island soils had an average soil pH of 7.0 (neutral) although soil pH varied
greatly between the Yap Island samples. The high soil pH found on the four islands of the Ulithi
Atoll was probably due to the formation of the Atoll which was formed by the upheaving of acoral reef while Yap Island was formed by a volcanic eruption. The soil EC was higher in soilsof the Ulithi Atoll Islands compared to those of Yap Island. Soil water content was very high intaro patch soils and low in soils of citrus and coconut plantings. Soil nitrogen content was highin some soil samples although soil nitrogen levels were low in most soils of all the islands surveyed. The high nitrogen samples could have resulted from the spreading of manure or fertilizer
on the sampled area by the inhabitants. The soil phosphate and potassium content was low in all
soil samples taken. Soil calcium and magnesium content was relatively high, however, it is notclear why the differences between islands exist.

Acknowledgments
The authors are grateful to Prof. G. A. Couvillon, University of Georgia, for proof reading
the manuscript.