Submitted to: Natural Organic Matter in Soils and Water North Central Region Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 3/22/2003
Publication Date: 3/22/2003
Citation: JOHNSON, J.M., CARPENTER-BOGGS, L., LINDSTROM, M.J. HUMIC ACID AND AGGREGATE STABILITY IN AMENDED SOILS. PROCEEDINGS OF THE NATURAL ORGANIC MATTER IN SOILS AND WATER NORTH CENTRAL REGION SYMPOSIUM. 2003. p. 21. Interpretive Summary:
Technical Abstract: Ethanol production from cellulosic material (e.g. corn stover) is being developed for commercialization. Part of a life-cycle analysis on the overall feasibility of using corn stover as a biofuel includes studies that address soil sustainability. After using stover for ethanol production, the remaining by-product of fermentation has 60 to 70% lignin. Lignin has been implicated as having a role in soil stabilization. The impact of lignin could be direct or lignin may contribute to the formation of humic acid, which increases soil stability. Aggregate stability is one measure of soil stability. It was hypothesized that humic acid concentration and aggregate stability should increase if lignin inputs were increased. Two soil core incubation studies were conducted. The first used three soils collected from the 0-15 cm layer from a Svea catena. The soils were Svea (fine-loamy, mixed, superactive, frigid Pachic Hapludoll) from the toe slope with 20 g organic C kg**-1 soil, Barnes (fine-loamy, mixed, superactive, frigid, Calcic Hapludoll) from the back-slope with 17 g organic C kg**-1 soil and Langhei (fine-loamy, mixed, superactive, frigid Typic Eutropdepts) from the shoulder slope with 3 g organic C kg**-1 soil. Air-dried and sieved soils were either not amended or amended with either corn stover (3 mm) or an analog of a stover fermentation by-product (712.5 g lignin, 140.0 g cellulose and 2.5 g hemicellulose kg**-1 soil). The soil cores were incubated at 60% water-filled pore space (WFPS) at nearly constant temperature (18-22 deg C) for 60 d. In the second study, only the Svea and Langhei soils were used. The soils were either not amended or amended with either corn stover (3 mm) or stover fermentation by-product (624 g lignin, 125 g cellulose and 28 g hemicellulose kg**-1 soil). The cores were brought to an initial WFPS of 60% and allowed to dry to 35% WFPS before watering to 60% WFPS. The air temperature varied from 14 to 32 deg C during the 123 d incubation. After the incubations, the soil was removed and allowed to air-dry. An aliquot of soil was used to extract crude humic acid. After rotary sieving, the 1 to 2 mm aggregates were remoistened to near field capacity and their aggregate stability was determined. On the Langhei soil, which has very low organic carbon, the concentration of humic acid (r**2=0.82) and aggregate stability (r**2 = 0.21) was increased linearly with lignin input regardless of the source of lignin. In addition, on the Langhei soil, aggregate stability increased linearly with the increased humic acid (r**2=0.27, P= 0.0001). If observed independently, these relationships were not seen on the Barnes or Svea soil. If all soils were included, a linear model (r**2 = 0.5) described the relationship between crude humic acid concentration and aggregate stability, but the exponential model (y = y**o+ae**bx; r**2=0.58) gave a better mathematical fit. Both of these models suggest a degree of stabilization in soil particles is due to factors that are not biological. The exponential model suggests a rapid increase in aggregate stability with increased humic acid. This assumes that after some critical value there would be little gain in aggregate stability with increased addition of soil humic substances.