Labile Soil Carbon As Impacted By Dryland Cropping Systems in Eastern Colorado.

The newer method of Permanganate oxidizable carbon (POXC) measures the labile soil carbon in a quick and inexpensive manner. POXC has been shown to have a positive correlation with particulate organic matter, microbial biomass C, and total soil organic matter. As you build SOC, magroaggregates form and later water stable microaggregates. It has been shown that this test is sensitive enough to detect differences in soils due to changes in management and environmental effects. We measured POXC at three long-term experimental sites that represent different soil types in eastern Colorado. These sites ranged from 16-27% clay content (Walsh being the lowest and Stratton being the highest content). This information helped us to (i) determine if oxidizable carbon will increase with cropping intensity and (ii) determine if there is a relationship between active C and water stable microaggregates in the soil. Soils were sampled at the summit of each site with wheat-fallow (WF), wheat-corn (sorghum)-fallow (WCF), and continuous cropped rotations (CC). All but the WF rotation has been in place for the past 30 years. We collected soil at three depths: 0-2.5 cm, 2.5-5 cm, and 5-10 cm from each treatment. Soil POXC content was greater in the shallower depths (0-2.5cm and 2.5-5cm) than in the 5-10 cm depth at all sites. The CC rotation had greater POXC than WCF at the two northern sites and there was no effect of rotation on POXC levels at the southern site with the lowest clay content across all sites. These results show clay content and residue input influence the quantity and distribution of labile soil C within the soil profile.