A tale of two systems: Does reducing tillage affect soil health differently in long-term, side-by-side conventional and organic agricultural systems?

Abstract

Tillage reduction is an increasingly common goal of farmers worldwide to reduce soil erosion and improve agroecosystem sustainability. Reduced tillage is usually achieved by different strategies in conventional and organic agricultural systems, yet it is unclear if these different strategies have contrasting effects on soil health. To compare how reduced-till strategies affect soil health under conventional and organic management, we evaluated soil health of a long-term field crop trial in Pennsylvania, USA. This trial was established in 1981 with three side-by-side management systems: an agrochemical-based conventional maize-soybean system (CNV), a legume-based low-input organic grain system (LEG), and a manure-based organic grain and forage system (MNR). Ten years after reduced-till treatments were introduced in 2008, herbicide-based no-till in the CNV system did not affect soil organic matter (SOM), cation exchange capacity, permanganate oxidizable carbon (POXC), or autoclaved-citrate extractable (ACE) protein content under conventional field crop production. Reducing tillage in the conventional system significantly increased potentially mineralizable carbon (PMC) by 23 ± 11%, and led to more severe surface compaction, reflected by 23 ± 9% shallower penetration resistance at 300 psi. In the LEG and MNR systems, tillage was reduced through cover crop-based rotational no-till, where maize and soybeans were no-till planted following the use of a roller-crimper to terminate fall-planted cover crops. In these two organic systems, moderately reducing tillage did not cause significant changes in individual soil health indicators except for a 17 ± 8% increase of PMC in the MNR system. Individual soil health indicators and Comprehensive Assessment of Soil Health (CASH) scores generally did not differ between the CNV and LEG systems, and were significantly higher in the longer-rotation, manure-based MNR system. These results suggest that soil health in organic systems was determined more by diversified crop rotations and adequate organic inputs than by reducing tillage frequency, whereas in conventional systems other co-adapting soil health practices might be necessary to alleviate surface compaction and realize the full benefits of reduced tillage.