Long‐term organic management combined with conservation tillage enhanced soil organic carbon accumulation and aggregation

Abstract

AbstractSuccessful synergy between organic management and conservation tillage could provide the best agroecological benefits by minimizing the negative effects of both synthetic chemicals and intensive tillage on soils. We studied the long‐term impacts of conventional and organic crop management under different tillage regimes on soil organic C (SOC) and soil aggregation, leveraging Rodale Institute's long‐term Farming Systems Trial. The experiment was initiated in 1981 with three cropping systems under intensive tillage management: (a) conventional (3‐yr rotation of corn–corn–soybean) with synthetic fertilizer application, (b) organic–legume (4‐yr rotation of corn–oats–soybean/wheat–wheat) organic system with legume as sole N source, and (c) organic–manure (8‐yr rotation of soybean/wheat–wheat/hay–hay–hay–corn silage/wheat–wheat–corn–oats) organic system with composted manure and legumes as N sources. There were eight replications for each of these cropping systems when the trial was initiated in 1981. In 2008, four replicates of each cropping system treatment were placed under conservation tillage management. Soils were collected from 0 to 10‐, 10 to 20‐, and 20 to 30‐cm depths in 2018 and measured for total SOC, active SOC fractions (microbial biomass C, water extractable C, permanganate‐oxidizable C), aggregate size distribution, and wet aggregate stability. Overall, total and active SOC increased by 16–132% under organic management compared with conventional management and the increase was more pronounced under organic–manure treatment than organic–legume treatment. Results also showed that 10 yr of tillage treatments did not influence active and total SOC concentrations, but influenced dry aggregate size distribution and wet aggregate stability. This study suggests that in long‐term organic cropping systems, incorporated composted manure and perennial hay vs. legumes alone accumulated the greatest amount of SOC compared with conventional systems. Conservation tillage in organic systems improved aggregation; however, beyond 10 yr, it is necessary to reflect tillage effects on SOC.