Cultivated soils in the Everglades are being converted to their historic use as pastures or seasonally flooded prairies as parts of restoration efforts, but long-term cultivation may have altered soil P distribution and availability which may pose eutrophication hazards upon change in land use. The objectives of this study were to determine the distribution of P in soil chemical and physical fractions for contrasting long-term land management practices. The distribution of P in labile, Fe-Al bound, Ca bound, humic-fulvic acid, and residual pools in five aggregate-size fractions were measured for fields under sugarcane (Saccharum sp.) cropping for 50 years and perennial pasture for 100 years. Both land uses were characterized by a high degree of macroaggregation, as aggregates >0.25 mm contained 76 and 83% of the total soil under cultivation and pasture, respectively. Soils under sugarcane sequestered a total of 77 kg ha-1 more P than pasture at 0-15 cm. The distribution of P in chemical fractions significantly varied between land uses as cultivation increased P sequestration in Ca-bound fractions more for sugarcane (244 kg P ha-1) than pasture (65 kg P ha-1). Pasture sequestered more P in organic pools, as storage in humic-fulvic acid and residual fractions were 26 and 25%, respectively, higher than sugarcane. Labile P was 100% higher for pasture than sugarcane, but Fe-Al bound P storage did not differ between land uses. Aggregation increased P sequestration in humic-fulvic acid and residual fractions, and P storage in organic pools increased with increasing aggregate size. In contrast, cultivation decreased aggregation and increased P accumulation in inorganic fractions. Long-term cultivation altered the distribution of soil P from organic to inorganic pools. The P stored in inorganic pools is stable under current land use, but may be unstable and pose eutrophication hazards upon onset of future land use change to the seasonally flooded prairie ecosystem.
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机译：作为恢复工作的一部分，大沼泽地的耕作土壤已转变为牧场或季节性洪水大草原的历史用途，但长期耕作可能会改变土壤磷的分布和可用性，这可能会因土地用途的变化而引起富营养化危害。这项研究的目的是确定磷在土壤化学和物理成分中的分布，以与长期的土地管理实践进行对比。在甘蔗（ Saccharum sp。）种植了50个甘蔗的田地中，测定了五种骨料级分中不稳定态，Fe-Al结合，Ca结合，腐殖酸和剩余池中P的分布。年，多年生牧场为100年。两种土地利用都具有高度的宏观聚集特征，聚集体> 0.25 mm分别占耕种和牧场总土壤的76％和83％。在0-15厘米处，甘蔗下的土壤固存的磷比牧场高出77 kg ha -1 。耕地之间化学组分中磷的分布差异显着，因为耕种使甘蔗（244 kg P ha -1 ）的钙结合部分中的磷固存比牧场（65 kg P ha ）多-1 ）。牧草在有机池中螯合了更多的磷，因为腐殖酸-富里酸和残存馏分中的磷分别比甘蔗高26％和25％。牧场中的不稳定磷比甘蔗高100％，但是在土地利用之间，铁铝结合的磷储量没有差异。聚集增加了腐殖酸-富里酸和残留部分中的P螯合，有机池中的P储存随着聚集体尺寸的增加而增加。相反，培养减少了无机部分的聚集并增加了P的积累。长期耕作改变了土壤磷从有机库向无机库的分布。无机池中存储的磷在当前土地利用下是稳定的，但在未来土地利用改变为季节性被洪水淹没的草原生态系统时，可能会不稳定并造成富营养化危害。
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