Study on minor elements of Ryukyuan soils. 1. Preliminary test by Spurway Soil Test Kit. 5. Soils from northern part of Okinawa-jima.

1. One hundred and ninty-seven soil samples from fifty-nine localities in northern Okinawa were taken and tested by the Spurway Soil Test Method for the same purpose as in the previous reports. 2. Magnesium was contained moderately in most soil samples, so there is little possibility of magnesium deficiency. These tests indicated that soils from northern Okinawa contained less Mg^ than those from southern Okinawa. 3. The soluble iron test in slightly alkaline soils was negative same as the soils in southern Okinawa. Even in acid soil, there were many samples showing low test with the reserve test which indicate the possibility of iron deficiency. 4. In the case of manganese (Mn^), many samples gave low test which indicates the possibility of manganese deficiency for plants. There were no samples showing toxic level of soluble manganese. 5. Test for sulfates (S0_4^) were negative in all of the soil samples. This indicates S04^ content is below toxic level. 6. Tests of other than the above elements were also made and the results are summarized as follows: a) NO_3^- and NH_4^+ content are generally low in almost all soil samples. b) Phosphorus content in most soil samples was very low and many of them gave less than 1 ppm. by the reserve test. c) Many samples showed less than 20 ppm. by the reserve test for potassium. However, samples from three localities gave abnormally high test by the reserve method which were considered as a result of past heavy fertilization. d) Ca^ content in most soil samples except the ones derived from palaeozoic limestone, Ryukyu Limestone and alluvial deposits were generally low which indic:tte the need of lime application for most high-lime requiring crops. e) Al^, Cl^- and NO_2^- were all below toxic levels. 7. Elements other than the above were not checked because the Spurway Soil Test Kit does not have such testing methods