At present, the definition and chemical analysis method of available soil phosphorus for plants have not been standardized because of the complexity of crop and soil characteristics in Korea and many analysis methods have been suggested with different extraction conditions. Suitable analytical method of available soil P should be established by the trial of various methods based on crop nutrition and soil conditions. To establish the most suitable analysis method of available soil P, a pot experiment with young maize was conducted over 44 different upland soils collected over the land of Korea. The amount of uptaken P by the plant was determined by ten different chemical methods for the available soil P.
The results obtained were as follows:
1. Total phosphorus content in the sample soils ranged 533∼4917 ppm, and showed significant positive correlation with the content of organic matter.
2. The P consent was relatively low in the acid sulfate soil and very high in the volcanic ash soil although both types of soil contained high level of orgic matter.
3. The amount of extractable P determined by ten different methods were varied more or less, and the ratios of the extractable P to the total soil P were in the range of 1∼48%.
4. The relative values to the amount of extractable soil P by different methods were in the order of
H₂O(5min.)(10.) $lt; H₂O(60min.)(2.27) $lt; NH₄HCO₃(5.57) $lt; NaHCO₃(7.42) $lt; Double lactate(9.71) $lt; Bray No.1(12.53) $lt; Lancaster(17.63) $lt; Nelson(25.96) $lt; AcOH(27.6) $lt; CAL-method(50.27).
5. The amount of extractable P determined by all of applied methods was very low in acid sulfate soil, volcanic ash soil and coarse textured soil.
6. Soil pH and total soil P generally showed significant positive correlation with the chemically extracted P, and soil organic matter was negatively correlated with the determined by Nelson-and CAL-method. Olsen method which showed significant correlation with exchangeable calcium seemed to be recommendable for calcareous soils.
7. Total amount of uptaken P by young maize through continuous twice cropping was 4.05% of total soil P in average, and the uptake in the second cropping was twice as much as that of the first cropping.
8. Three determination methods, i.e. Soltanpour-, Double lactate-, and Bray No. 1-method seemed to be more suitable than Lancaster method which is widely practiced at present in Korea. However, further study should be carried out with other crops and soils to most adequate chemical method for determination of available soil P.
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