降低pH對鹼性土壤中磷有效性與可溶性的影響

Effects of Decreasing pH on Phosphorous Availability and Solubility in Alkaline Soils

李雪甄(Hsueh-Chen Li) ； 莊愷瑋(Kai-Wei Juang)

《臺灣農業化學與食品科學》 49卷3期 (2011/06) Pp. 99-110

https://doi.org/10.6578/TJACFS.2011.013

摘要

As pH decreased by amendment of acidifying materials in alkaline or calcareous soil, soil P becomes more releasable, thus increasing P availability and also P loss into the environment. The objective of this study was to investigate the effects of decreasing pH on P availability and solubility in alkaline soils. Four agricultural soils (Chengchung, Lukang, Taikang, and Tapais) of Taiwan, whose pH range from 7 to 8, were used for investrgation. The soils were amended with five levels of P (0, 25, 125, 250 and 500 mg/kg) and incubated for 90 days. Then their pHs were adjusted to two target ranges (5-6 and 6-7) using HCl followed by a stabilization period for 2 weeks. The available P indices, Bray No. 1, Olsen, and Mehlich 3 methods, and the soluble P indices, water and CaCl(subscript 2) extractions, for each soil sample were measured. In the results, pH decreasing to 5-6 and 6-7 significantly resulted in raise of available P in Taikang and Tapais soils which contain relatively high calcium carbonate equivalent and Mehlich 3 extractable Ca but low oxalate extractable Fe. However, for Lukang soil which contains extremely high oxalate extractable Fe, there was no significant raise of available P with decreasing pH. Because Chengchung soil contains relatively high oxalate extractable Fe, there was less enhancement of P availability due to decrease of pH, when high levels of P was applied. Moreover, the water extractable P in the four soils showed soluble P significantly reduced with decreasing pH. When the Tapais soil was adjusted to pH 5-6, the soluble P increased probably due to a large amount of Ca-P precipitates under this condition. Therefore, decreasing pH to the value of 6 to 7 for Tapais, Taikang, and Chungcheng soils could simultaneously increased P availability and reduced P solubility; nevertheless, decreasing pH to lower than 6 for Tapais soil could increase soluble P. Decreasing pH for Lukang soil could reduce soluble P but could not increase P availability. In summary, decreasing pH will increase P availability and reduce soluble P in the alkaline soils which contain relatively high Ca content but low Fe and Al oxides. However, decreasing pH for the alkaline soils with high Ca content and Fe and Al oxides can only reduce soluble P but not raise availability of P.

關鍵字

有效性磷 ； 可溶性磷 ； 土壤檢測磷 ； 磷固定 ； 石灰質土壤

並列摘要

As pH decreased by amendment of acidifying materials in alkaline or calcareous soil, soil P becomes more releasable, thus increasing P availability and also P loss into the environment. The objective of this study was to investigate the effects of decreasing pH on P availability and solubility in alkaline soils. Four agricultural soils (Chengchung, Lukang, Taikang, and Tapais) of Taiwan, whose pH range from 7 to 8, were used for investrgation. The soils were amended with five levels of P (0, 25, 125, 250 and 500 mg/kg) and incubated for 90 days. Then their pHs were adjusted to two target ranges (5-6 and 6-7) using HCl followed by a stabilization period for 2 weeks. The available P indices, Bray No. 1, Olsen, and Mehlich 3 methods, and the soluble P indices, water and CaCl(subscript 2) extractions, for each soil sample were measured. In the results, pH decreasing to 5-6 and 6-7 significantly resulted in raise of available P in Taikang and Tapais soils which contain relatively high calcium carbonate equivalent and Mehlich 3 extractable Ca but low oxalate extractable Fe. However, for Lukang soil which contains extremely high oxalate extractable Fe, there was no significant raise of available P with decreasing pH. Because Chengchung soil contains relatively high oxalate extractable Fe, there was less enhancement of P availability due to decrease of pH, when high levels of P was applied. Moreover, the water extractable P in the four soils showed soluble P significantly reduced with decreasing pH. When the Tapais soil was adjusted to pH 5-6, the soluble P increased probably due to a large amount of Ca-P precipitates under this condition. Therefore, decreasing pH to the value of 6 to 7 for Tapais, Taikang, and Chungcheng soils could simultaneously increased P availability and reduced P solubility; nevertheless, decreasing pH to lower than 6 for Tapais soil could increase soluble P. Decreasing pH for Lukang soil could reduce soluble P but could not increase P availability. In summary, decreasing pH will increase P availability and reduce soluble P in the alkaline soils which contain relatively high Ca content but low Fe and Al oxides. However, decreasing pH for the alkaline soils with high Ca content and Fe and Al oxides can only reduce soluble P but not raise availability of P.

並列關鍵字

Available P ； Soluble P ； Soil test P ； P-fixation ； Calcareous soil