Organic matter levels in soil affect the flexibility of cultural practices, the impact of drought, the earliness of getting on the land, and the amount of CO2 released. Low levels of organic matter in association with compacted soils may influence mechanical impedance of roots. Root growth in compacted low organic-matter level soils is not well understood, but it can be assumed that the extra energy required for root growth is not available for yield. Farmers today may have to return to the former practice of plowing down organic matter to maintain crop productivity and reduce erosion (Fig. 14-1).