Washington has become the first US state to legalize human composting, where people can elect to have their body turned to soil after death, as an alternative to cremations and burials.

The bill, signed by Governor Jay Inslee on Tuesday, aims to reduce pressure on crowded graveyards in inner city areas, and allows loved ones to use the soil for cultivation.

Katrina Spade, whose company Recompose will provide the service in Washington, says the process offers a natural and safe alternative to traditional burials which reduces carbon emissions and land usage.