Agricultural practices affect the status of legacy phosphorus (P) in soils and consequently the P bioavailability and susceptibility of losses to water resources. Previous studies have primarily assessed P status within agroecosystems, and rarely have these results been compared to native conditions. We evaluated the effects of long-term (45 years) consistent cropping [continuous corn (CC), corn-oats-alfalfa-alfalfa rotation (CR), and continuous bluegrass sod (CB)] with and without P fertilization on changes in P fractions of different bioavailability in a Brookston clay loam, as compared to an adjacent forest native soil. Soil P was separated into various inorganic P (P_i) and organic P (P_o) fractions using a modified sequential fractionation method. Phosphorus in native soil was predominated by moderately labile P_o (NaOH-P_o), 44%, followed by moderately stable P_i (HCl-P), 26%. Compared to the native soil, consistent cropping without P fertilization significantly decreased all P fractions except for water-extractable P_o, with the largest decrease in labile P_i (water-P_i + NaHCO₃-P_i) and moderately labile P_o of 65 and 73 mg kg^–1, respectively, over 45 years. Consistent cropping with fertilization retained comparable amount of total P in CC and RC, but increased total P in CB, relative to the native soil. Averaged over cropping systems, labile P_i, NaOH-P_i, and HCl-P increased by 129, 74, and 20 mg kg^–1, respectively, whereas labile P_o and moderately labile P_o decreased by 8 and 60 mg kg^–1, respectively, compared to the native soil. This study indicates that long-term cropping significantly enhanced the rate of moderately labile P_o mineralization, irrespective of fertilization. The increases of total P and P_o in the fertilized CB plots suggest that P accumulation in long-term grass fields is a concern as far as potential P contamination in surface waters.

农业实践影响土壤中遗留磷（P）的状况，因此影响磷的生物利用度和水资源损失的敏感性。先前的研究主要评估了农业生态系统中的磷状况，很少将这些结果与自然条件进行比较。我们评估了长期（45年）一致施肥[连续玉米（CC），玉米燕麦-紫花苜蓿-苜蓿轮作（CR）和连续蓝草草皮（CB）]施肥和不施磷对磷素变化的影响与邻近森林原生土壤相比，布鲁克斯顿粘土壤土具有不同生物利用度的部分。土壤P被分为各种无机P（P _i）和有机P（P _o）分数，采用改进的顺序分馏方法。天然土壤中的磷以中等不稳定的P _o（NaOH-P _o）为主要成分，为44％，其次是中等稳定的P _i（HCl-P），为26％。相比于天然的土壤，而不施P一致裁剪显著下降均P馏分除了水提取磷_ø，在不稳定的P中的最大下降_我（水-P_我+的NaHCO ₃ -P_我）和适度不稳定P _ø的65和73 mg kg ^–1分别超过45年。与施肥相一致的耕作，相对于天然土壤，CC和RC的总P保持相当的水平，但CB的总P却增加了。在整个种植系统中，不稳定的P _i，NaOH-P _i和HCl-P分别增加129、74和20 mg kg ^–1，而不稳定的P _o和中度不稳定的P _o减少8和60 mg kg ^–与天然土壤相比分别为¹。这项研究表明，无论施肥如何，长期种植都显着提高了中度不稳定的_PO矿化速率。总P和P _o的增加 受精的CB地块中的磷表明，长期表层土壤中的P积累与地表水中潜在的P污染有关。