Effect of Tillage and Carbon Input Levels on Carbon and Nitrogen Dynamics Over the Long-Term

EPA Grant Number: U916177
Title: Effect of Tillage and Carbon Input Levels on Carbon and Nitrogen Dynamics Over the Long-Term
Investigators: Hooker, Bethanie A.
Institution: University of Connecticut
EPA Project Officer: Graham, Karen
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $105,964
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Fellowship - Terrestrial Ecology and Ecosystems , Ecological Indicators/Assessment/Restoration


The objective of this research project is to study the effect of tillage and carbon input levels on long-term carbon and nitrogen dynamics. The influence of cropland carbon (C) on atmospheric CO2 levels is receiving increasing attention in research and policy arenas. Cropland can function as a sink or a source for atmospheric CO2 (Karlen and Cambardella, 1996). For example, soils under no-till management have been shown to contain longer-lived (i.e., more slowly decomposed) C than conventionally tilled soils, in which soil is churned, a process which activates and accelerates decomposition. No-till soils are believed to sequester carbon, thus reducing the overall amount of C in the atmosphere as CO2. As a result, the use of conservation tillage, such as no-till, has been promoted as part of a strategy to reduce C loss from agricultural soils (Kern and Johnson, 1993). Currently, the U.S. Environmental Protection Agency (EPA) is exploring avenues whereby cropland can be used to generate carbon "credits" that would theoretically offset carbon emissions from fossil fuel combustion. Unfortunately, our current understanding of the processes and pathways that govern whether carbon from crop residue is retained in the soil or released as atmospheric CO2 is far from complete. However, if agricultural management and policy goals aimed at reducing atmospheric CO2 are to be achieved, these processes must be understood. In their recent book examining agricultural soil processes and their links to the global C cycle, Lal, et al., (1998) emphasize that agricultural research priorities must now include understanding the principle processes for C sequestration in soils, and understanding the relative significance of agricultural, agroforestry, and pasture management practices to C sequestration.


Another aspect of intensive agriculture which is receiving attention is leaching and gaseous losses of nitrogen (N) (such as the strong greenhouse gas N2O). Although increasing fertilizer N has greatly improved crop yields, and the amount of C in new plant biomass, these practices have led to leaching and gaseous losses of N, representing not only environmental problems, but also economic losses to the farmer (Matson, et al., 1997). These losses are driven by the mismatch between the timing of fertilizer N availability in soil and the timing of plant uptake through the season (Robertson, et al., 2000). Management practices capable of reducing this mismatch in time could significantly increase nutrient use efficiency of crops and decrease negative environmental impacts of intensive agriculture (Mosier, et al., 1998).

At the University of Connecticut Plant Science Research Farm, I have access to a remarkable set of corn fields that have been maintained in silage corn (stover removed each year) or grain corn (stover is left to decompose on site) under no-till or conventional till management regimes, with three replicates, for 30+ years. Paul, et al. (1997) established a network of 35 long-term sites covering dominant corn, wheat, and soybean regions in the United States and Canada, and standardized data from these sites have been taken for parameterizing and testing mathematical models. No New England site is included in this network (Paul, et al., 1997; Paustian, et al., 1995); the closest site is Rodale, in Pennsylvania. Also, though management practices in the network include combinations of various tillage and fertilizer regimes, crop rotations, and residue management strategies, in no case were common silage and grain corn harvest techniques combined with no-till and conventional till management in a long-term (> 20 year) experiment (Rasmussen, et al., 1998).

For my research project, I propose a set of experiments in these long-term agricultural plots exploring treatment-induced patterns in short-term and long-term carbon and nitrogen dynamics. These patterns and mechanisms are dependent on the soil type, the climate, and the specific management regimes used here.

It is hoped that by using these data in conjunction with larger cross-climate, cross-region data sets already in the agricultural community, the results of this research will help test empirical and mechanistic models of C sequestration and N loss. Ultimately, these models may provide accurate predictions of soil organic carbon (SOC) sequestration and N trace gas flux under a variety of climatic and management regimes.

Supplemental Keywords:

fellowship, tillage, cropland carbon, atmospheric carbon, carbon sequestration.

Progress and Final Reports:

  • 2003
  • 2004
  • Final