Woody perennial cropping systems have the potential to produce food while maintaining or improving soil health relative to annual cropping systems. We used space-for-time substitution to assess soil health improvements by a Chinese chestnut – pawpaw agroforestry (AF) system in Iowa, USA relative to corn – soybean rotation (CSR), representing conventional annual crop management, and secondary forest (SF), which served as a natural woody perennial ecosystem reference point for improved soil health. We also compared several Chinese chestnut (Castanea mollisima Blume) and pawpaw (Asima trilobal (L.) Dunal) AF guilds, including single and double density chestnut monoculture, pawpaw monoculture, and chestnut and pawpaw polyculture, to evaluate the effects of tree density versus diversity on soil health. We found significant improvements in biogeochemical metrics of soil health for a mature (24 years old) AF system established on fields previously in annual crop production, relative to an adjacent no-till CSR system. Surface soil (0–30 cm depth) total and microbial stocks of carbon and nitrogen in the agroforestry system were greater in AF than in CSR, but less than in the SF. Soil carbon stocks down to one meter increased from CSR (62.7 Mg C ha^-1 ± 3.22 SE) to AF (72.1 Mg C ha^-1 ± 2.23 SE) and SF systems (80.8 Mg C ha^-1 ± 4.46 SE), but did not differ between the two perennial systems. Acid - base chemistry in surface soils was similar between AF and CSR, but SF ecosystems had significantly higher pH, CEC_e, and percent base saturation than both cropping systems. We found few effects of AF guild (i.e. groupings of woody crop species) on the biogeochemical metrics of soil health, suggesting that modest increases in woody perennial crop density and diversity did not lead to further improvements to soil health. Overall, land conversion to agroforestry from annual crop production improved soil health and increased soil carbon sequestration.

与一年生种植系统相比，木本多年生种植系统具有生产粮食的潜力，同时保持或改善土壤健康。我们使用时空替代来评估美国爱荷华州栗木-木瓜农林业 (AF) 系统相对于玉米-大豆轮作 (CSR)（代表传统的一年生作物管理）和次生林 (SF) 对土壤健康的改善情况，作为改善土壤健康的天然木质多年生生态系统参考点。我们还比较了几种板栗 ( Castanea mollisima Blume) 和木瓜 ( Asima trilobal (L.) Dunal) AF 公会，包括单密度和双密度板栗单一栽培、木瓜单一栽培以及栗子和木瓜混养，以评估树木密度与多样性对土壤健康的影响。我们发现，相对于相邻的免耕 CSR 系统，在以前一年生作物生产领域建立的成熟（24 岁）AF 系统的土壤健康生物地球化学指标显着改善。农林业系统中表层土壤（0-30 cm 深度）的碳和氮总量和微生物储量在 AF 中高于 CSR，但低于 SF。土壤碳储量低至一米，从 CSR (62.7 Mg C ha ^-1 ± 3.22 SE) 增加到 AF (72.1 Mg C ha ^-1 ± 2.23 SE) 和 SF 系统 (80.8 Mg C ha ^-1± 4.46 SE），但两个多年生系统之间没有差异。AF 和 CSR 之间表层土壤的酸碱化学相似，但 SF 生态系统的 pH 值、CEC _e和碱饱和百分比显着高于两种种植系统。我们发现 AF 公会（即木本作物物种的分组）对土壤健康的生物地球化学指标几乎没有影响，这表明木本多年生作物密度和多样性的适度增加并未导致土壤健康的进一步改善。总体而言，从一年生作物生产向农林业转变的土地改善了土壤健康并增加了土壤碳固存。