中部土壤所含磷形態與稻穀收量及磷吸取量之關係

Abstract

利用磷形態分佈，以研究土壤中有效態磷供應狀況，過去多以盆栽為主，田間資料缺乏。本試驗之用的在探討中部土壤所含磷形態對於盆栽與田間稻穀收量與磷吸取量之關係，俾供改進稻田磷肥管理與估計計磷肥供應之參考。經在本省中部（南投、影化、雲林及臺中）四種不同類別土壤土，選取20地點，同時舉行盆找與田問試驗以及室內化驗，所得結果摘要於下： 土壤中全磷及各形態磷含量與土壤母質及其化學性狀有密切關係。點板岩沖積土全磷含量最高，以Ca-P為主。其次為砂頁岩沖積土，以Fe-P為主。再次為混合沖積土，則以Ca-P與Fe-P為主。 稻穀收量或磷吸下量與土壤中各形態磷之關係，經單相關與複相關計算結果，以及栽培前後土壤中各形態磷之變異情形，均顯示水稻所攝取之磷以Fe-P為主；但Ca-P與一有機磷則有干撓作用，尤其在田間更為顯著，因而田間水稻磷吸取量與Fe-P之相關係數顯然較盆栽者為低，相對地降低其重要性。 在盆栽情形，水稻磷吸取量與土壤PH亦呈極顯著之負相關，而在田間更與粘土及有機物含量各呈顯著之負相關；相反地，土壤中Ca-P與有機磷之含量則與土壤pH、粘土及有機物含量有密切之正相關。因此，土壤中Ca-P與有機磷阻礙水稻磷吸不者，可能主要受土壤pH與粕土及有機物含量之影響。 綜上所言，水稻磷吸取量確與土壤中Fe-P有關，但其相關程度，在田間不如盆栽者強，此可能因在盆栽不排水情形與田間自然環境之下，由於粘土與有機物呈現不同效應所致。 The application of phosphorus fractionation to the study of plant available phosphorus has been applied by several workers. However, most of them were conducted in pot culture. Information regarding the response of rice plant to various forms of soil phosphorus in field conditions is still in meager. This experiment was carried out for understanding the relationship of soil P-fraction to grain yield as well as P-uptake of rice plant under both pot culture and field conditions in order to find out the behavior of soil phosphorus between them. Twenty field trials were conducted on four categories of alluvial soils (sandstone and shale alluvial soil, slate older alluvial soil, slate recent alluvial soil, and mixed alluvial soil) scattered in central Taiwan. Soil samples for pot culture were taken from the sites where field trials had been carried out. The result may be summarized as follows: 1. The analysis of total phosphorus content showed that slate alluvial soil was the highest, sandstone and shale alluvial soil, the second, and mixed alluvial, the third. 2. The result of soil phosphorus fractionation indicated that the slate alluvail soils were dominant in Ca-P, the sandstone and shale alluvial soils in Fe-P, and the mixed alluvial soils in both Ca-P and Fe-P. The Al-P and organic-P occupied in the range of 4-7 % and 14-20% of the total phosphorus of the soils, respectively. It was also found that the amount of various forms of soil phosphorus had much to do with the nature of the soils, such as pH, clay, organic matter, CEC, exchangeable Ca and Mg, and free iron oxides. It was worthwhile to mention that remarkably positive correlation was found between soil Ca-P and soil pH, and between soil organic-P and clay. 3. In comparing the change in the amount of total phosphorus and various forms of phosphorus before and after 4 consecutive cropping of rice in pot culture, it was found that the content of total phosphorus was higher in the soils treated with phosphorus but lower in the soils received no phosphorus. The Ca-P almost remained constant in the soil without phosphorus, but increased in the soils with phosphorus. The increase in organic-P was also found in the soils with phosphorus. The other forms of phosphorus including A1-P, Fe-P, and occluded-P decreased, more or less in all soils regardless whether phosphorus had been added or not . Although the transformation of various forms of soil phosphorus is influenced by the nature of the soil and cultural practices, highly positive correlation between P-uptake and Fe-P reduced in the soil treated with-out phosphorus after cropping was obtained. It provided the evidence that Fe-P was the main source of phosphate absorbed by rice plant under submerged condition. 4. The results of simple and multiple correlation of soil phosphorus to P-uptake also indicated that soil Fe-P was the main source of phosphate absorbed by rice plant. On the contrary, soil Ca-P was negatively correlated with P-uptake under both pot culture and field conditions. Furthermore, significantly negative correlation between P-uptake and soil organic-P was also found in field conditions. Consequently, the relative importance of soil Fe-P increasing P-uptake was minimized in field conditions. 5. Negatively close relationship of P-uptake to soil pH was found in both pot culture and field conditions. In addition, contents of clay and organic matter were also negatively correlated with P-uptake in field conditions at significant level. As mentioned before, soil Ca-P and organic-P was positively correlated respectively with soil pH and clay. Thus the inhibition of P-uptake of rice plant by Ca-P and organic-P may be attributed to pH and clay content of the soils tested. In conclusion, phosphorus uptake of rice plant was highly related to soil Fe-P in pot culture provided without drainage, but less in field conditions. It is due probably to the difference in the function of clay and organic matter between them.