The researchers studied how to tell if compost made from biogas residues and spent mushroom substrate is mature enough for plants to grow well. They looked at how the compost changed physically and chemically over time. They found that certain parameters like organic carbon, nitrogen levels, and certain nutrients can show if the compost is ready for plants. The compost that was 100% mature showed better plant growth than regular seedlings. This means that using specific measurements can help determine if compost is good for plants to grow in.