Identification of Factors That Aid Carbon Sequestration in Illinois Agricultural Systems

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Illinois Digital Environment for Access to Learning and Scholarship Repository Contract Report 2003-02 Identification of Factors that Aid Carbon Sequestration in Illinois Agricultural Systems by Edward C. Krug and Steven E. Hollinger Prepared for the Illinois Council on Food and Agricultural Research (C-FAR) March 2003 Illinois State Water Survey Atmospheric Environment Section Office of the Chief Champaign, Illinois A Division of the Illinois Department of Natural Resources Identification of Factors that Aid Carbon Sequestration in Illinois Agricultural Systems Edward C. Krug and Steven E. Hollinger FINAL REPORT to Illinois Council on Food and Agricultural Research (C-FAR) on Contract IDACF 02E 14 5 WS Steven E. Hollinger Principal Investigator Illinois State Water Survey 2204 Griffith Drive Champaign, Illinois 61820-7495 March 2003 Identification of Factors that Aid Carbon Sequestration in Illinois Agricultural Systems Executive Summary Soil organic carbon (SOC) sequestration is important to climate change and cropland agriculture. Crops naturally use the greenhouse gas, carbon dioxide (CO2), from the atmosphere; the greater the crop productivity the greater the amount of CO2 used. Agronomic practices that enhance sequestration of crop biomass in soil as SOC also enhance removal of CO2 from the atmosphere, and improve and sustain soil fertility. To effectively reduce the concentration of CO2 in the atmosphere and mitigate climate change, sequestration of SOC must be long term, defined as decades or longer. This report presents a review and synthesis of scientific understanding of SOC sequestration, based on the history and genesis of soils and vegetation in Illinois, and the response of SOC and crops to agronomic practices. Recommendations for future cropland SOC research are made. In order to improve the quantity and permanence of SOC sequestration, it is necessary to understand the soil-forming factors responsible for SOC sequestration in Illinois. Five interactive soil-forming factors are widely recognized (biology, parent material, climate, topography, time); however, the literature shows that human activity can be considered a sixth soil-forming factor. Human activities affect the soil-forming factors which govern SOC sequestration. Native American land-use practices of whole ecosystem manipulation were important in governing soil formation and SOC contents in Illinois, as were the land-use practices of the settlers who displaced them. Most of Illinois is covered by geologic parent materials produced by the last Ice Age and the typical (modal) Corn Belt cropland soils of Illinois were formed from such geologic parent materials covered by tall-grass vegetation that was frequently burned by Native Americans and lightning. The frequent burning maintained tall-grass prairie over most of Illinois. Numerous soil analyses conducted during the early 20th Century showed that modal Corn Belt soils developed under Illinois’ tallgrass prairies had two to three times the SOC of their forest soil counterparts in the top 1 meter (m). Fire frequency largely governed the distribution of forests and prairies. Forests covered only about one-third of pre-settlement (before ~1750) Illinois and were located mostly in landscape elements whose topography hampered fires. Therefore, the pre-settlement distribution of forest and prairie was determined largely by three soil-forming factors: topography, climate, and Native Americans. Research conducted on humid, temperate natural areas (prairies and forests) of 20th Century North America indicate why such a great SOC difference in prairie and forest soils developed. Whereas both ecosystems produce comparable amounts of biomass, most forest biomass is aboveground and most prairie biomass is belowground where it is more efficiently incorporated into SOC. Furthermore, prairie biomass has higher concentrations of nitrogen (N) and other nutrients necessary to convert decaying biomass into humus — soil organic matter (SOM). Given the location of prairie biomass and its nutrient content, more prairie biomass becomes humus and therefore, a lesser proportion is lost to the atmosphere as CO2 gas relative to forest biomass. Research indicates that presettlement forests and prairies of Illinois had greater biological productivity, turnover, and SOC content than their natural area counterparts of the 20th Century. Fire regularly burned presettlement prairies and enhanced overall prairie productivity, ii aboveground animal life, belowground microbial and animal activity, growth of legumes, and wetness. Fire produced charcoal — black porous carbon — which robust presettlement prairie microfauna and macrofauna incorporated more than 1 m into the soil. All of these factors coalesced to enhance SOC sequestration and SOC contents to levels greater than the 20th Century prairies, which have neither the fire frequency, legume richness, nor aboveground and belowground animal ecologies of presettlement prairies. Presettlement forests had a higher fire frequency that made for more fire-resistant tree species, a lower density of trees, and maintenance of a rich groundcover of herbs, legumes, and grasses that supported abundant wildlife. Most presettlement forests in northern, central, and southern Illinois were described as open and park- like, with a grassy, herbaceous, legume-rich groundcover of prairie plant species. Such forests would have developed more SOC-rich soils than 20th Century Illinois forests. Changes in natural area forest and prairie SOC are believed to be much slower than those induced by plowing and other cropland agronomic practices. However, literature shows that rapid and large changes occur in prairies and forests with decreased fire frequency and animal activity. Such ecological changes result in SOC changes equal to or exceeding those reported for agronomic practices. For example, increased fire frequency increased SOC by 50 percent in the top 15 centimeters (cm) of a forest floor in about a decade by stimulating the growth of grasses and legumes. Conversely, protection of prairie from fire and grazing resulted in woody plant invasion and a 40 percent SOC decrease in the top 3 m in just 40 years. Additionally, after a century under forest, a prairie soil profile was converted morphologically into a forest soil profile. This analysis of the history and genesis of soils and vegetation in Illinois shows that human manipulation of soil-forming factors can have a tremendous impact on SOC sequestration. Native American land-use practices influenced SOC. A more accurate estimate of the natural area SOC sequestration potential can be achieved by including the effect of the removal of Native Americans and cessation of their land-use practices. Current SOC sequestration potential estimates have excluded this important factor. Traditional agronomic cropland practices also influence SOC by manipulating soil-forming factors through plowing, draining, crop harvest, and erosion in ways that accelerate soil SOC losses. On average, 40 percent of plow layer SOC has been lost from cultivated prairie and forest Corn Belt soils compared to the SOC found in equivalent natural area soils. However, whole-soil SOC change — SOC changes in the top 2+ m of soil — has yet to be quantified. This is an important task, especially for prairie-derived Corn Belt soils, because in the top 1.5 m of soil, over 80 percent of SOC lies below the plow layer. Time was assessed as a soil-forming factor for SOC contents of soil-development sequences, also called soil-maturity sequences. Chronological age is not an adequate definition of time because the “effective age” of a soil is also influenced by the other soil-forming factors. As soils develop, the most easily weatherable minerals are released; a portion is lost from the soil, a portion is taken up by plants, and a portion is stored in plant-available form in SOM. As soils continue to develop, their banks of SOM and plant-available nutrients grow to maturity, i.e., achieve their maxima. As soils age past their peak productive years, they become more acidic. With increased acidity and decreased P and K, N fixation and biological productivity decrease. Because formation and maintenance of soil humus requires N, P, sulfur (S), and other nutrients, all of the above factors conspire to reduce SOC sequestration in post-mature soils as effective age increases. In such aging soils, fine-soil aggregates produced by plant and animal pedoturbation decrease, with loss of aggregation becoming more pronounced with soil depth. As a result, soil structure becomes more massive, and SOM becomes less exposed to (more protected from) iii decomposition by already diminished weathering capacity of biological activity. The age of bulk- soil SOC increases as turnover rates decline; however, old SOC quickly decomposes locally around roots by the high biological activity of the rhizosphere, and SOC turnover is greater than that inferred from bulk-SOC age. Aged soils can be rejuvenated — acidity neutralized, and nutrients restored — naturally and/or by anthropogenic activities. With rejuvenation, root systems become larger and older SOC is available to the high biological activity of the rhizosphere. The discrepancy between actual SOC turnover rate and SOC turnover rate inferred from bulk-SOC age becomes even larger with rejuvenation. In recent decades, herbicides and pesticides have enabled the widespread practice

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