Mechanical weeding effects on soil structure under organic vegetables

Summary

Mechanical weeding of vegetables involves the repeated use of cultivators and tractors. This repeated tillage and compaction changes soil structure. We studied these changes in fields of organic beans and carrots. Structure was described using visual assessment and by measuring soil strength. Under beans, the soil strength below the growing root zone was highly variable and in some areas was strong enough to restrict root growth. The carrots were grown in beds containing zones of crop and bare, weeded soil. The structure of the weeded soil in the top 10 cm layer eventually became disrupted and compacted enough to deter root growth. In addition the topsoil and subsoil in the wheel-tracks between the beds became very compact with little distinguish-able structure. This compaction extended to the sub-soil and persisted into the next cropping season.