Iron tubes (IMAGE) American Society of Agronomy Caption PVC pipes painted with rust, known as IRIS tubes, help track how much oxygen is in the soil. When there isn't enough oxygen, microbes will turn the rust into regular iron, which washes away. These tubes are drying after being extracted from the experiments and rinsed. Credit J.C. Fiola Usage Restrictions For use with this story only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.