Soil microaggregate and macroaggregate decay over time and soil carbon change as influenced by different tillage systems

Soil tillage can affect the formation and stability of soil aggregates. The disruption of soil structure weakens soil aggregates to be susceptible to the external forces of water, wind, and traffic instantaneously, and over time. The choice of tillage system or land management changes the soil physical condition and soil organic matter content, which is an essential factor in building soil aggregates. This study was conducted to investigate the effects of different tillage systems on the rate of decay of different sizes of soil aggregate fractions and other associated properties over time as subjected to a continuous wetting process. This research was conducted on a long-term tillage study, established in 2002 at the Iowa State University Agronomy Research Farm near Ames, Iowa. The soil association in this study is Clarion-Nicollet-Webster (Clarion [fine-loamy, mixed, mesic, Typic Hapluduolls], Nicollet [fine-loamy, mixed, mesic, Aquic Hapluduolls], and Webster [fine-loam, mixed, mesic, Typic Endoaquolls]). The experimental design was a randomized complete block design with four replications. Main plot treatments were five tillage systems: moldboard-plow, chisel-plow, deep-rip, strip-till, and no-till. The cropping system was corn (<i>Zea mays</i> L.)–soybean (<i>Glycine max</i> L.) rotation. Wet aggregate stability was measured using the Wet Sieving Apparatus (Eijkelkamp, Agrisearch Equipment. Art no. 08.13). Soil organic carbon (SOC) and soil total nitrogen (N) were analyzed by dry combustion using CHN Analyzer (TruSpec CHN Version 2.5x). Results show no-till with the highest carbon (C) content and the highest macro- and microaggregate stability over time. The findings also show a strong relationship between the increase in SOC content and the stability of macro- and microaggregate under continuous wetting process. Furthermore, the findings suggest that aggregate stability and moisture content are highly correlated with SOC content, and the rate of decay of both aggregate sizes (macro and micro) is highly influenced by the intensity of tillage. The implication of this research is the importance of no-till not only in increasing the stability of micro- and macroaggregates and SOC storage, but also in its effect on increasing the stability of all aggregate fractions in continuous wet conditions for extended periods of time.