Paddy Soils in Tropical Asia: Part 5. Soil Fertility Evaluation
摘要
According to the Survey Manual,D Soil fertili ty is the q uali ty that enables the soil to provide the proper compounds in the proper amounts and in the proper balance for the growth of specified plants when other factors such as light, temperature, moisture, and the physical condition of the soil, are favorable. Thus, by definition the chemical nature of a soil determines its fertility. For paddy soils the importance of soil physical properties or tilth is relatively minor because of their specific man agement condition of I waterlogging. Therefore, soil fertility should deserve a higher attention in attempt to evaluate the capability of paddy soils. There have been many attempts to evaluate soil fertility in different countries or regions, such as the ones known as land capability classification and the Storie Index. In all these methods so far proposed contributing factors have been only subjectively evaluated and the final result has been presented usually in a qualitative form. Even the Survey Manual says that Soil fertili ty is not directly observable. Thus, soil may be grouped into fertility classes only by inference. Then is it not possible to evaluate soil fertility quantitatively, and to attain a fertility classification in a more objective and reproducible way? In an attempt to answer this challenging question we have proposed a method of fertility evaluation particularly intended for paddy soils 2 ,8,4) and a few preliminary applications of it made on tropical Asian paddy soils. 5 ,6,n In this paper the results of the most recent study along the same line are presented.