土壤樣本乾燥程度對於磷鉀有效指數的影響

Effect of Drying on the Availability Index of Soil Phosphorus and Potassium

林家棻(Char-Fen Lin) ； 李子純(Tze-Shun Lee Wang) ； 王幼惠(Yu-Hwea Wong)

《中華農業研究》 21卷4期 (1972/12) Pp. 233-249

https://doi.org/10.29951/JARC.197212.0004

摘要

本文之目的乃探討土壤樣本乾燥後，對於磷、鉀有效指數之影響，與土壤性質、作物收量以及磷、鉀吸收量之關係；同時并探討其抑制方法。經選用20種本省主要土壤之樣本，予以不同乾燥處理後，分別用兩種磷、鉀速測法加以測定，所得結果摘要如下：
(1)田間濕土經乾燥後，磷有效指數因個別土壤而變異，或增或減，相差甚大。在Bray氏法中平均較田間濕土增加25%~40%，其變異幅度與土壤之C.E.C大小有關。在Mehlich氏法中磷有效指數之變異幅度較Bray氏法爲低，可能因土壤中Al-P及Fe-P受烘乾之後，變異甚大，而Ca-P則較小所致。就平均數而言，風乾、曬乾或40℃烘乾約較田間濕土增加5%~7%，但110℃烘乾者可提高至32%，其變異幅度與粘土，Fe-P，及Ca-P等含量有關。
(2)田間濕土經乾燥之後，鉀有效指數普遍提高。在醋酸銨法中，平均較田間濕土增加15%~17%，烘乾者可達30%，而在Mehlich氏法中則可提高至28%~34%，110℃烘乾者可達49%，其變異情形與土壤之C.E.C成顯著之正相關。
(3)烘乾前加Doxtrose，或風乾後加水濕潤，或施以Octanol處理，確可抑制磷、鉀因乾燥而釋放，但無法將個別土壤完全恢復至與田間濕土一致。
(4)利用Neubuaer法檢定土壤，經不同乾燥處理後，所得磷、鉀有效指數與稻苗乾重或磷、鉀吸收量之相關情形，顯示Mehlich氏法不適於稻田速測之用，Bray-P所得之相關係數，以田間濕土最高，且達極顯著平準，其次爲再濕潤處理或Octanol處理，亦達顯著或極顯著平準；風乾、曬乾或烘乾處理者最低，甚至有未達顯著平準。但Bray法應用於鈣質土壤時，其相關係數有減低趨勢。Mehlich-K及醋酸銨－K之相關係數均達極顯著平準，烘乾者其相關係數較田間濕土者有更高之趨勢，此可能因為烘乾可提高鉀有效指數之測定值。而在Neubauer法栽培之下，所用土壤有限，但播種量高，其相關係數受土壤中鉀量(Quantity)之影響較鉀強度(Intansity)爲大。
因此就土壤速測值與作物收量或PK吸收量之相關而言，樣本乾燥對於土壤中Al-P及Fe-P變異甚大，利用Bray's法測定時，以田間濕土爲宜，對於Mehlich-K及醋酸銨－K之影響雖然較小，但因K之釋放受乾燥溫度之影響甚大，樣本乾燥條件必須一致，否則將影響推薦量估計之偏差。

並列摘要

The aim of this study was to find out the effect of drying on the soil PK and its relation to dry matter content as well as PK-uptake of rice seedlings. The control of PK-releasel/fixation on drying by addition of chemicals was also involved.
Twenty soil samples including 8 main soil groups of Taiwan were taken for study. Each soil sample was treated with four methods of drying and determined by two extrac-tants. To control PR-release/fixation on drying, chemical compounds (dextrose/octanol/water) were added either before or after drying. The relation between soil P and P-uptake as well as soil K and K-uptake was detected by the Neubauer test in which rice was used instead of rye seeds and soil was kept under submerging condition. The results may be summarized as follows:
1. The effect of drying on the availability index of soil P was extremely great especially in the case of the Bray P-1 test. However, the average increase of soil P-value on different methods of drying as compared to that of field moist soil was at 25%-40% for the Bray's method and 5%-32% for the Mehlich's method. The decrease was also found in Schist alluvial soils. The change of soil P on drying was found to be related to the C.E.C. and the contents of clay, Al-P, Fe-P, and Ca-P of the soil.
2. The soil K was almost unanimously increased by drying. However, the magnitude of increase was different from soil to soil. The average increase as compared to that of field moist soil was 15%-30% and 20%-49% for the ammonium acetate and Mehlich's method, respectively. The C. E. C. was one of the dominant factors in responsoring the change of soil K on drying.
3. The control of PR-release/fixation on drying by addition of dextrose/octanol/water was found effective for certain soil but not for all soils.
4. Evidences from Neubauer test indicated that the available P determined by Bray's method with undried soil samples gave the best estimation of plant-available P in the soil. Those with air-dry rewet as well as air-dry octanol treated improved the estimation of available P over those obtainable with either air-dry or oven-dry soils. The relation-ships of Mehlich's P to the dry matter content or to the P-uptake of rice seedlings were insignificant. Soil K-value measured by ammonium acetate method was significantly related to the dry matter content as well as to K-uptake of rice seedlings in spite of drying effect. It was also true in the case of Mehlieh's method. As the release of soil K was closely related to the drying temperature, the condition for drying soil samples should be carefully controlled in order to avoid a fictitious recommendation for K fertilization.