Accumulation of the gaseous hormone ethylene helps roots sense compact soil.

Soil compaction, in which soil grains are pressed together leaving less pore space for air and water, is a persistent problem in mechanized agriculture. Most plant roots fail to penetrate soil if it is too dense. One might assume that they are physically unable to penetrate the compact soil. However, new research demonstrates a more complex mechanism that requires the build-up of the volatile plant hormone ethylene in the rhizosphere 1 . Ethylene itself can arrest growth and, in compact soil, it is present in higher concentrations near roots due to its reduced ability to diffuse. Roots that lack the ethylene response pathway grow better through compact soil, demonstrating that it is physically possible to do so. The work suggests new levers for crop improvement in increasingly degraded soils.