Long‐term agricultural experiments in the Coastal Plain of the southeastern United States are needed to understand biogeochemical processes and design better systems to overcome a changing climate and other perturbations. We determined a suite of soil organic C and N fractions after 19 yr of management from a diverse farming system project in Goldsboro, NC. Soil was collected at 0‐ to 6‐, 6‐ to 12‐, and 12‐ to 20‐cm depth increments from 14 treatments that were subsets of five overarching treatments of conventional cropping, integrated crop–livestock systems, organic cropping, plantation forestry, and old‐field successional land use. Surface residue C and N were greater with woody (i.e. plantation forestry and successional) than with cropping systems (7,491 and 2,896 kg C ha⁻¹, respectively; 138 and 60 kg N ha⁻¹, respectively). Soil‐test biological activity was greater with alternative cropping (i.e. integrated crop–livestock and organic systems) than conventional cropping (314 vs. 220 kg CO₂–C ha⁻¹ 3 d⁻¹, respectively). An integrated crop–livestock system with grazed pasture in long rotations with crops had greater net N mineralization than hayed forage in shorter rotations (111 vs. 92 kg N ha⁻¹ 24 d⁻¹, respectively). Total organic C and particulate organic N concentrations were highly stratified with depth, but stocks were not different between conventional and no‐till cropping when summed to 20 cm. We conclude that alternative cropping systems with forage‐based rotations, limited tillage, and organic inputs can create long‐lasting improvements in soil organic C and N fractions than conventional agricultural and more naturalized systems.

中文翻译：

---

在北卡罗来纳州沿海平原进行了19年耕作制度研究之后，土壤碳和氮含量

为了了解生物地球化学过程并设计更好的系统以克服气候变化和其他干扰，需要在美国东南沿海平原进行长期农业试验。经过19年的管理，我们从北卡罗来纳州戈德斯伯勒的一个多样化农业系统项目中确定了一套土壤有机碳和氮组分。从14种处理中以0至6、6至12和12至20 cm的深度增量收集土壤，这些处理是常规耕种，作物-牲畜综合系统，有机作物，人工林的五种总体处理的子集，以及旧土地的连续土地利用。木本植物（即人工林和演替林）的表面残留物C和N大于种植系统（分别为7491和2896 kg C ha ^-1； 138和60 kg N ha^-1）。与常规种植相比，替代种植（即作物-牲畜和有机系统一体化）的土壤试验生物活性更高（分别为314 vs. 220 kg CO ₂ –C ha ^-1 3 d ^-1）。轮作放牧的牧草与农作物的综合畜牧系统在较短的轮作中比干草草料有更高的净氮矿化度（111 vs. 92 kg N ha ^-1 24 d ^-1， 分别）。总有机碳和有机氮的浓度在深度上高度分层，但常规耕作和免耕作物的总蓄积在20 cm时没有差异。我们得出的结论是，与常规农业和更自然化的系统相比，具有基于牧草的轮作，有限的耕作和有机投入的替代种植系统可以长期改善土壤有机碳和氮组分。