Quantification of a sensitive soil carbon constituent as affected by soil type, tillage system, and crop rotation

The objectives of this research were to develop a method by which to assess the total potential release of reducing sugars from soils and then to use that method to assess the effects of soil type, tillage system, crop rotation, time, and physio-spatial distribution on that soil organic carbon pool.;Findings of this research demonstrated that the decrease in rate of production of reducing sugars as the value of total reducing sugars released reached Rr was due to a decrease in the substrate pool from which these monosaccharides were nascent. After five days of incubation, concentrations of total reducing sugars released matched calculated R r values. Therefore, incubation of field-moist surface soil (0-15 cm) for five days at 30°C in 60% methanol solution was used to estimate Rr and to assess the impacts of soil type at different locations, tillage system, and crop rotation on the total potential reducing sugar carbon pool.;Tillage, crop rotation, and location all significantly impacted the concentration of releasable reducing sugar in soils. On average, soil from the no-till system exhibited mean concentrations of 7.5 and 19.9 mg kg-1 soil more releasable reducing sugars than chisel-plow and moldboard plow tillage systems, respectively. The chisel-plow tillage system had concentrations that were, on average, 12.3 mg kg-1 soil greater than the moldboard plow tillage system. In general, releasable reducing sugar concentrations were 2.4 mg kg-1 soil greater in continuous corn than corn-soybean rotation. Although of different magnitude, the trends of these management effects were the same regardless of location.;The effects of a temporal variable on these releasable reducing sugar concentrations were significant; the impact of one single spring secondary tillage treatment was assessed and was found to be significant. Regardless of tillage management system, results show that releasable reducing sugar concentrations in soils had, on average, significantly decreased the following spring when compared to concentrations analyzed from samples that were collected the previous fall. Furthermore, when soil reducing sugar concentrations of spring baseline (prior to spring secondary tillage), were compared to concentrations after a single secondary tillage pass, concentrations averaged 18% lower in the moldboard plow tillage system, 6.9% lower in the chisel plow tillage system, and 9% greater in the no-till system (which was used as a control). Changes in reducing sugar concentrations during this six-day time period in the corn-soybean rotation, were as follows: decreases of 18.7% in reducing sugar concentration with moldboard plow tillage system, 8.3% with the chisel plow tillage system, and an increase of 11% with no-till were noted compared to decreases of 17.4%, 5.4%, and an increase of 6.9% for the same tillage treatments, respectively, in the continuous corn cropping system.;Analysis of the physio-spatial distribution of releasable reducing sugars in field-moist soil aggregates from no-till, chisel plow, and moldboard plow surface (0-7.5 cm) and subsurface (7.5-15 cm) soil samples demonstrated that soil aggregates of size fractions 1-2 and 2-4 mm held the greatest concentrations of releasable reducing sugars. A stratification effect was noted in the no-till system, where the average concentration of releasable reducing sugars from all aggregate fractions was 63.9 mg kg-1 in the top 0-7.5 cm surface soil and 33.4 mg kg-1 in the 7.5-15 cm subsurface soil depth. Average concentrations were more homogenized in the other tillage systems with greater concentrations in subsurface soil (7.5-15 cm), and significantly greater concentrations in chisel plow subsurface soil depth than in the moldboard plow subsurface soil depth. (Abstract shortened by UMI.).