Soil phosphorus characteristics and reaction of soil phosphorus to different fertilizers under different rotation systems and fertilization management for eleven years

為暸解經長期不同施肥管理之後，所引起 土壤磷的肥力及化學性質改變，本試驗取 高雄農改場在高雄縣旗山鎮砂岩及黏板岩 混合沖積土設置的有機農耕法長期試驗田 的六種土壤，做添加肥料之孵育試驗。六 種土壤分別為採自兩種輪作系統﹙第一輪 作系統，代號R1；第二輪作系統，代號R2﹚， 各系統分設有機農耕法﹙代號O﹚，慣行農 耕法﹙代號I﹚及折衷農耕法﹙代號C﹚等 三種處理。本試驗利用土壤的孵育，研究 長期不同施肥管理下的各土壤對相同施肥 量，而不同來源添加磷的反應。土壤孵育 分為四種施肥處理，即不添加任何肥料物 質之對照組、施化學肥料、施豌豆渣堆肥 及施牛糞堆肥，在田間容水量下進行孵 育。化學肥料之施用為50 - 25 - 40（N - P2O5 - K2O）mg kg-1。有機肥料則為含50 mg kg-1 的磷酐。於第30 天、90 天、150 天測 定其各磷有效性的變化， 且利用修正 Hedley 的序列萃取法，以不同強弱的萃取 劑來劃分土壤中的磷，將孵育150 天的土 壤磷劃分為水溶性磷、碳酸氫鈉萃取有機 磷及無機磷、氫氧化鈉萃取有機磷及無機 磷、鹽酸萃取磷及殘餘磷，並探討經長期 不同施肥處理及不同來源添加磷的影響。 另利用McLean (1979) 提出的速測法的觀 念，測定孵育不同時間的土壤於添加水溶 性磷二小時後之固定率，由此可了解不同 施肥管理對土壤的磷肥力狀況及磷肥的固 定趨勢。 結果顯示，有機農耕法有較高的磷有 效性，且在各孵育階段也都有較高的磷有 效性。三種農耕法土壤，添加磷的孵育試 驗中，均隨時間增加而增加Bray-1 磷的含 量。大部分土壤經孵育後，隨時間的增加 而有較高的表觀磷回收率。在土壤劃份磷 的部份，各土壤中都存在相當多量的鹽酸 可萃取磷，即難利用性磷所佔比例甚多。 有機農耕法土壤有最高的碳酸氫鈉萃取無 機磷含量，慣行農耕法次之，折衷農耕法 最少；而在不同輪作系統下的比較，則顯 現第一輪作系統之土壤比第二輪作系統者 的碳酸氫鈉萃取無機磷的含量高，而添加 不同磷來源的結果，以添加牛糞堆肥者的 碳酸氫鈉萃取無機磷的含量較高，而添加 化學肥料者的含量較少。To understand the changes in chemical characteristics and transformation of soil phosphorus (P) after long-term fertilization management, six soils from a branch station of Kaoshiung District Agricultural Improvement Station were investigated in this incubation study. The six soils from the Improvement Station were under two long-term crop rotation systems with three kinds of fertilization management, i.e., organic farming, conventional farming and intermediate farming, respectively. Soil samples for incubation study and analysis were drawn from a depth of 0-20 cm of each plot and passed through a 0.85 mm sieve. The incubation study consisted of a chemical fertilizer, two compost treatments, and a without fertilizer addition control. Soil of 500 g was completely mixed with the fertilizer and incubated under field capacity (-33.3 kPa ) in a plastic bag with several pores for exchange of gas. The composts were added to the soil at the rate of 50 mg P2O5 kg-1 soil on a dry weight basis and that of chemical fertilizer was 50-50-40 (N-P2O5-K2O ) mg kg-1. A complete 8 × 4 factorial design with three replications was adopted. All samples were incubated at 25 ± 3 ℃. Deionized water was added to bring the soil moisture to its initial value every three days. Soils were sampled after 30, 90, and 150 days of incubation. The Bray-1 P, Olsen P, and apparent P recovery were determined at each sampling. Soil P fractions were determined by modified Hedley sequential fractionation procedure for samples of 150 days’ incubation. The results indicated that the Bray-1 and Olsen extractable P of organic farming soil were higher than those of the other soils. The same tendency of the effect of fertilization history on Bray-1 and Olsen extractable P existed during incubation. Bray-1 P of all soils was increased with incubation time. The apparent P recovery also increased with incubation time for most of the soils. The HCl extractable P concentrations of the soils were the highest among various P fractions. Sodium bicarbonate solution extractable inorganic P of organic farming soil was higher than that of conventional farming soil and that of the intermediate farming soil the lowest. The sodium bicarbonate solution extractable inorganic P of soil of rotation system 1 was higher than that of rotation system 2. The sodium bicarbonate solution extractable P of the soil treated with dairy dung compost was the highest and that treated with chemical fertilizer the lowest among the four treatments that treated just before incubation. In conclusion, the P fertility and P chemistry of soil were significantly affected by the fertilization history and less affected by short-term application of adequate amount of fertilizer.