Developing meaningful agroecosystem soil P inventories necessitates moving beyond single measures of readily extractable inorganic P (P_i) limited to surface depths. We drew on a long-term (36 year) experimental field trial in the US Maize Belt (northwestern Illinois) to evaluate how crop rotation [maize-maize (Zea mays L.) vs maize-soybean (Glycine max L. Merr.)] and N fertilization (0 vs 269 kg N ha⁻¹) impact P dynamics throughout the soil profile by using sequential fractionation and phosphatase activity assays, contextualized by soil P stocks and agronomic P balances. Distribution of P fractions by depth (0–15, 15–30, 30–60, 60–90 cm) indicate that management effects were limited to the surface soil layers (0–30 cm). Soil P fractions differed more by depth than by experimental treatments. Long-term N fertilization significantly decreased pH concurrently with labile organic P (P_o) and phosphodiesterase activity. Soil labile inorganic P (P_i) was two-fold lower under N fertilization compared to zero N fertilization, reflecting greater yield and thus P export via grain harvest. Under N fertilization, integration of soybean elevated soil phosphodiesterase activity and decreased water-extractable P_o. Higher stocks of soil P_o than labile P_i at surface depths (0–30 cm) corroborated a hypothesized appreciable pool size of soil P_o relative to the labile P_i pool to which most agronomic assessments are limited. Large negative agronomic balances over the 36-year period (−426 to −945 kg P ha⁻¹) are suggestive of legacy P from pre-experiment manure application and high native P stocks, with net P export equivalent to 11–35% of soil P stocks at 0–90 cm depth at the initiation of the experiment. These results contribute to a better understanding how N fertilization and rotation practices influence soil P cycling and stocks, thereby informing P budgets for comprehensive agroecosystem P management.

开发有意义的农业生态系统土壤 P 清单需要超越仅限于表面深度的易于提取的无机 P (P _{i ) 的单一测量。}我们在美国玉米带（伊利诺伊州西北部）进行了一项长期（36 年）的田间试验，以评估作物轮作 [玉米-玉米 ( Zea mays L.) 与玉米-大豆 ( Glycine max L. Merr.) ] 和 N 施肥（0 对 269 kg N ha ^-1) 通过使用连续分馏和磷酸酶活性测定影响整个土壤剖面的 P 动态，由土壤 P 库存和农艺 P 平衡背景化。P 组分按深度（0-15、15-30、30-60、60-90 cm）的分布表明管理效果仅限于表层土壤层（0-30 cm）。土壤 P 分数在深度上的差异比在实验处理上的差异更大。长期施氮肥显着降低了 pH 值，同时不稳定的有机磷 (P _o ) 和磷酸二酯酶活性也随之降低。土壤不稳定无机磷（P _i) 与零氮施肥相比，施氮肥低两倍，反映了更高的产量，因此通过谷物收获输出磷。在施氮肥的情况下，大豆的整合提高了土壤磷酸二酯酶的活性，降低了可水提取的 P _o。在地表深度（0-30 厘米） ，土壤 P _o储量高于不稳定 P _{i库，证实了假设的土壤 P o}池大小相对于大多数农艺评估受限的不稳定 P _i池。36 年期间出现大量负农艺平衡（-426 至 -945 kg P ha ^-1) 表明来自实验前施肥和高原生 P 库的遗留 P，在实验开始时，净 P 输出相当于 0-90 cm 深度土壤 P 库的 11-35%。这些结果有助于更好地理解施氮和轮作如何影响土壤磷循环和库存，从而为全面农业生态系统磷管理的磷预算提供信息。