Abstract. Modern agricultural systems rely on inorganic nitrogen (N) fertilization to enhance crop yields, but its overuse may negatively affect soil properties. Our objective was to investigate the effect of long-term N fertilization on key soil properties under continuous corn [Zea mays L.] (CCC) and both the corn (Cs) and soybean [Glycine max L. Merr.] (Sc) phases of a corn-soybean rotation. Research plots were established in 1981 with treatments arranged as a split-plot design in a randomized complete block design with three replications. The main plot was crop rotation (CCC, Cs, and Sc), and the subplots were N fertilizer rates of 0 kg N ha⁻¹ (N0, controls), and 202 kg N ha⁻¹, and 269 kg N ha⁻¹ (N202, and N269, respectively). After 36 years and within the CCC, the yearly addition of N269 compared to unfertilized controls significantly increased cation exchange capacity (CEC, 65 % higher under N269) and acidified the top 15 cm of the soil (pH 4.8 vs. pH 6.5). Soil organic matter (SOM) and total carbon stocks (TCs) were not affected by treatments, yet water aggregate stability (WAS) decreased by 6.7 % within the soybean phase of the CS rotation compared to CCC. Soil bulk density (BD) decreased with increased fertilization by 5 % from N0 to N269. Although ammonium (NH₄⁺) did not differ by treatments, nitrate (NO₃−) increased eight-fold with N269 compared to N0, implying increased nitrification. Soils of unfertilized controls under CCC have over twice the available phosphorus level (P) and 40 % more potassium (K) than the soils of fertilized plots (N202 and N269). On average, corn yields increased 60 % with N fertilization compared to N0. Likewise, under N0, rotated corn yielded 45 % more than CCC; the addition of N (N202 and N269) decreased the crop rotation benefit to 17 %. Our results indicated that due to the increased level of corn residues returned to the soil in fertilized systems, long-term N fertilization improved WAS and BD, yet not SOM, at the cost of significant soil acidification and greater risk of N leaching and increased nitrous oxide emissions.

中文翻译：

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连续玉米和玉米-大豆管理下施氮36年后的土壤性质

摘要。现代农业系统依靠无机氮（N）施肥来提高农作物的产量，但是过度使用它可能会对土壤特性产生负面影响。我们的目的是研究长期施用氮肥对连续玉米[ Zea mays L.]（CCC）以及玉米（Cs）和大豆[ Glycine max L. Merr。]（Sc）阶段土壤关键性状的影响。玉米-大豆旋转。研究区建立于1981年，其处理方法是在三个完整重复的随机完整区组设计中以拆分区设计的方式进行安排。主要地块为作物轮作（CCC，Cs和Sc），子图为N肥料施肥量为0 kg N ha ^-1（N0，对照），202 kg N ha ^-1和269 kg N ha ^-1（分别为N202和N269）。36年后，在CCC中，与未施肥的对照相比，每年添加N269显着提高了阳离子交换能力（CEC，在N269下提高了65％）并酸化了土壤的顶部15厘米（pH 4.8对pH 6.5）。土壤有机质（SOM）和总碳储量（TCs）不受处理的影响，但与CCC相比，CS轮作大豆期内的水团聚体稳定性（WAS）降低了6.7％。从N0到N269，随着施肥量的增加，土壤容重（BD）降低了5％。尽管铵（NH ₄ ⁺）在处理上没有差异，但硝酸盐（NO _3）−）与N0相比，N269的含量增加了八倍，这意味着硝化作用增强。与施肥地（N202和N269）的土壤相比，CCC下未施肥的对照土壤的有效磷水平（P）高出两倍多，钾（K）高出40％。与氮肥相比，氮肥施用可使玉米平均增产60％。同样，在N0条件下，旋转玉米的产量比CCC高45％。施氮量（N202和N269）使作物轮作效益降低至17％。我们的结果表明，由于施肥系统中返回土壤的玉米残留量增加，长期施氮改善了WAS和BD，但未改善SOM，但代价是土壤酸化显着，氮浸出风险增加和亚硝酸盐增加氧化物排放。