Aggregate Turnover Controls on Soil Organic Matter: The Influence of Management and Mineralogy

Colorado State University, Fort Collins CO

Investigators

Abstract

Soil disturbance from tillage is a major cause of organic matter and carbon loss from agricultural ecosystems, which contributes to the buildup of atmospheric CO2 and can lead to a loss of fertility. No-till cropping systems, in which crops are planted without tillage, have been shown to increase soil organic matter (i.e. carbon) levels and improve soil physical properties. However, the extent of soil organic matter improvement with no-tillage management varies between soils and the mechanisms of organic matter stabilization in no-tillage systems are unclear. The investigators' previous research has suggested that the buildup and stabilization of carbon under no-till is closely linked to the dynamics of soil aggregates, conglomerations of primary mineral particles and organic matter which range in size from 50 to > 2000 microns. The objective of the project is to develop a unified explanation of how aggregate dynamics control organic matter cycling that is applicable across domains of soil properties and soil disturbance regimes. A tracer approach will be employed to measure rates of aggregate formation and degradation, along with physical fractionation techniques to isolate aggregate-associated organic matter fractions. Fundamental knowledge of aggregate dynamics and the turnover of associated soil organic matter is central to understanding ecosystem function because it explains basic controls on nutrient cycling and soil water relationships. Further it will help in quantifying the degree to which no-tillage systems can be managed to sequester carbon, as a way to mitigate increasing CO2 in the atmosphere. This new understanding will also provide us the information needed to implement fully quantitative ecosystem simulation models with a new core concept for soil organic matter dynamics.