Soil strength after 21 years of conventional and organic cropping practices in the Mid-Atlantic region, USA

Soil compaction negatively impacts soil physical properties and crop yields and is influenced by organic matter inputs and tillage management. We evaluated cone index (CI) in five long-term organic and conventional cropping systems at the Farming Systems Project in Beltsville, MD (39.0°N, 76.9°W), to understand how different management systems influence soil strength. Measurements were collected prior to planting corn in 2017 using a tractor-mounted hydraulic five-probe penetrometer for three depths (0–15, 15–30, 30–50 cm) and three positions relative to the crop row (0, 22.5, and 45 cm). The two conventional systems, No-till (NT) and Chisel Till (CT), were both 3-yr corn-rye cover crop/soybean–wheat/soybean rotations. The three organic systems were comprised of: (Org2) 2-yr hairy vetch cover crop/corn-rye cover crop/soybean; (Org3) 3-yr hairy vetch cover crop/corn-rye cover crop/soybean–wheat; and (Org6) 6-yr corn-rye cover crop/soybean–wheat–alfalfa–alfalfa–alfalfa. Org2 and Org3 exhibited the lowest CI in the 0–15 cm depth, due to fall tillage before cover crop planting and weed control in the prior crop. In contrast, surface soil compaction in Org6 was similar to that in the conventional systems, attributed to alfalfa harvest machinery traffic over the past three years and absence of any tillage. At deeper depths (15–30 cm and 30–50 cm), the NT system consistently demonstrated lower CI compared to other systems. For tilled systems, maximum CI values at 15–30 cm were near or exceeded the root-restricting threshold of 2.5 MPa. The NT system potentially provided a larger rooting volume for water and nutrient uptake than tilled systems. Machinery traffic increased compaction, particularly at 22.5 cm from the crop row, likely due to tire sidewall pressure. Overall, the study found moderate effects of contrasting management system practices on soil strength. • Cone Index (CI) was determined in long-term organic and conventional cropping systems. • The 2-yr and 3-yr organic rotations had lower CI at 0–15 cm, likely due to recent tillage. • Averaged across systems, maximum CI was generally less than 2.5 MPa for the 15–30 cm depth. • For conventional systems, CI was lower in NT compared to CT at 15–30 cm. • Below 15 cm, the NT system consistently demonstrated lower soil strength compared to all other systems.