利用酸性改良劑降低粘板岩石灰性土壤pH值對土壤中鉀行為的影響

Abstract

摘 要 石灰性土壤因含碳酸鹽尤其是CaCO3，以及高pH值之緣故，致使土壤中K／(Ca+Mg)比太小，植物不易利用土壤中的鉀。以酸性物質之添加來降低土壤pH值，為改良石灰性土壤的方法之一，唯以酸性物質改良石灰性土壤時對鉀行為影響之相關研究仍有限，仍需探討及評估。本研究之目的在探討以硫磺粉與硫酸鋁降低石灰性土壤pH值時，對土壤中鉀行為的影響。選取碳酸鈣含量差異大之五種石灰性土壤，分別添加不同劑量之硫磺粉與硫酸鋁，並於25℃，-33 kPa田間容水量下進行培育試驗，使各供試土壤pH值降低至約7.0及6.5，培育期間測定土壤pH值、各型態鉀含量，培育後測定pH值、各型態鉀、鈣、鎂含量及鉀的Q/I關係。鹿港與圳寮土壤分別施入高量(h)及低量(l)之硫磺粉(S)及硫酸鋁(AlS)兩種酸性改良劑，於25℃及田間容水量下培育八週，培育期後風乾再施入0, 150 mg /kg鉀(K0, K150)於25℃及田間容水量下培育四週。另於相同的溫度及田間容水量下，供試土壤先施入0, 150mg/kg鉀培育四週，風乾後再施入不同含量(h, l)之兩種酸性改良劑培育八週。所有土壤樣品培育共十二週後，分別測定土壤pH值、各型態鉀、鈣、鎂的含量及鉀的Q/I關係。結果顯示硫酸鋁改良五種黏板岩石灰性土壤初期可獲得較施用硫磺粉者釋出較多的土壤溶液鉀，長期培育後黏板岩石灰性老沖積土仍能保持高量的溶液鉀，而試驗前後之黏板岩石灰性新沖積土之土壤溶液鉀含量則無顯著差異。添加酸性改良劑於土壤可促進土壤非交換性鉀的釋出，但非交換性鉀含量較低，農業活動較頻繁之員林土壤則出現鉀的固定作用。酸化石灰質土促使土壤ARKo下降至1×10-3(mol/L)1/2甚至更低，會使土壤鉀之供應不利於植物中長期生長時吸收利用，而高的PBCK值顯示應施用大量的鉀肥及減少鉀肥施用的頻率。先添加硫磺粉後添加鉀肥之鹿港土壤造成後添加的鉀肥在土壤中以溶液鉀的型態為主，添加較低量的硫磺粉之處理則能提升土壤交換性鉀量。後添加不同量的硫磺粉對土壤中三態鉀的分布影響較小，此現象亦出現在先添加硫酸鋁的處理，後添加硫酸鋁的處理則促進鉀離子的吸附增加交換性鉀量，添加高量的硫酸鋁促進鉀離子的吸附增加量較低。後施入的鉀肥無法被改良後之圳寮土壤吸附或固定，而先施入鉀肥之處理因部分的鉀吸附在特定位置或進入礦物層間固定，之後添加的酸性改良劑並不能交換出這些位置的鉀。本試驗鹿港與圳寮土壤ARKo值的下降顯現施入硫磺粉和硫酸鋁培育後供應植物鉀的能力均較未試驗的原土壤低，試驗後高的PBCK值顯示若欲再施鉀肥則可施用大量的鉀肥及減少鉀肥施用的頻率。先施用鉀肥培育後，再施用低量的硫酸鋁為以施用硫磺粉或硫酸鋁改良石灰性的鹿港與圳寮土壤時最佳的改良策略。

Abstract

Carbonates, particularly CaCO3, in calcareous soils with a high soil pH, result in a K/(Ca+Mg) value that is very small and the plants cannot efficiently use the potassium. One way to improve calcareous soil is to lower its pH value by applying acidic amendments. However, research on the effect of the acidic amendments on the behaviors of K in calcareous soils is limited and further assessments are required. The objectives of this study were to investigate the behavior of K when sulfur(S) and aluminum sulfate[Al2(SO4)3‧14H2O] (AlS) were applied to reduce the pH of calcareous soils. Five calcareous soils with different CaCO3 levels were examined. Incubation was performed while different amounts of S and Al2(SO4)3‧14H2O were applied to the soil until the soil pH was lowered to 7.0 and 6.5 under the condition of 25℃ and -33kPa water potential. The pH values, and the concentrations of different forms of K in the soils were measured throughout the incubation period. The pH values, various concentrations of forms of Ca, Mg and K as well as the quantity/intensity (Q/I) relationships of K were measured after the incubation. An eight week incubation period was performed while different amounts of S and Al2(SO4)3‧14H2O were applied to the Lukang and Chunliao soils until the soil pH was lowered to 7.0 and 6.5 under the condition of 25℃ and -33kPa water potential. After air dry, the soil incubated four weeks with 0, 150 mg K/kg under the same temperature and water potential. The another incubation were added K fertilizer then applied S and Al2(SO4)3‧14H2O. The pH values, and the concentrations of different forms of K in the soils were measured throughout the incubation period. After a twelve week incubation period, the pH values, various concentrations of forms of Ca, Mg and K as well as the quantity/intensity (Q/I) relationships of K were measured after the incubation. The result of applying acidic amendments to five types of soils indicated that more solution K was released than S when applying Al2(SO4)3‧14H2O during the initial stage. A rich concentration of solution K was retained in these five types of soils, even after being incubated for eight weeks. The addition of acid amendments promoted the release of non-exchangeable K in slate calcareous alluvial soils. Nevertheless, a fixation did occur for soils with a lower non-exchangeable K content and frequently farming such as the Yuanlin soil. Acidification of calcareous soil lowered the ARKo to be as low as 1×10-3(mol/L)1/2 or less. This result did not improve the soil supply of K to the plants after the short term. However, the high potential buffering capacity of K (PBCK) indicated that the frequency of using K fertilizer should be reduced, and a large amount of K fertilizer should be needed. The result of applying S then adding K fertilizer to Lukang soil indicated that most added K fertilizer in soil was solution K. Lower quantity of S applied could increase exchangeable K in Lukang soil. The S which added than K fertilizer was less effect three K forms in soil. In the other the Al2(SO4)3‧14H2O added was increased th soil exchangeable K but increased less in higher Al2(SO4)3‧14H2O added treatment. After applying acidic amendments, the K fertilizer that added then acidic amendments didn't absorb or fix with Chunliao soil. Before the acidic amendments adding, K fertilizer provided more specific sites K on soil minerals, and the added acidic amendments can't adsorb it. Acidification of calcareous soil lowered the ARKo value. This result did not improve the Lukang and Chunliao soils supply of K to the plants then check. However, the high potential buffering capacity of K (PBCK) indicated that the frequency of using K fertilizer should be reduced, and a large amount of K fertilizer should be needed. After K fertilizer incubation, applying lower quantity of Al2(SO4)3‧14H2O is the best method to improve calcareous Lukang and Chunliao soil with S or Al2(SO4)3‧14H2O.