Tillage Effects on Aggregate Turnover and Sequestration of Particulate and Humified Soil Organic Carbon

Abstract

The seasonal dynamics of soil organic carbon (SOC) fractions and dry aggregates were investigated to determine whether aggregate turnover rates explain the variable influence of no‐till (NT) practices on SOC accrual in Illinois. Soils were collected (0–15 cm) of two 17‐yr‐old trials where NT and conventional tillage (CT) practices had variable effects on SOC sequestration in the 0‐ to 30‐cm depth. Soil was fractionated into loose particulate organic matter (LPOM), macroaggregate‐occluded particulate organic matter (OPOM), and humified fractions (HFs) associated with microaggregates and minerals. Dry aggregate mean weight diameter (DMWD) was used to evaluate structure expressed in the field. Within‐season changes in fraction concentrations indicate that C derived from LPOM and plant roots was transferred to OPOM at both sites. At DeKalb (silty clay loam), NT practices had less influence on SOC sequestration than at Monmouth (silt loam). DeKalb HF contents increased under NT while OPOM contents were unchanged. At Monmouth, NT practices increased SOC sequestration by increasing OPOM concentrations. Site‐based differences in SOC accrual were related to aggregate turnover rates, which were increased by NT practices at Monmouth but were unaffected by tillage at DeKalb. Trends in DMWD and aggregate turnover suggest that when aggregate turnover is slow, as at DeKalb, OPOM formation is limited. Slow turnover in the heavier soil permitted accumulation of HF because residues had longer contact times with particle surfaces. When aggregate turnover is faster, as in the Monmouth NT soil, there is greater chance for residue incorporation into aggregates and accumulation of OPOM. Rapid aggregate turnover limits opportunities for mineral affiliation and HF accrual. Aggregate dynamics predicted site‐based differences in the form and rate of SOC accrual caused by the use of NT practices.

Influence of tillage practices on soil biologically active organic matter content over a growing season under semiarid Mediterranean climate

“…This finding is consistent with that reported in other studies (Willson et al, 2001;Yoo & Wander, 2008). Therefore, when these variables are used as indicators of soil responses to specific management practices, one must take seasonal variations into account.…”

“…2). The highest C-and N-POM figures were recorded in July 07, and may have been due to the roots and crop residues left after the wheat harvest (Yoo & Wander, 2008). Values for C-and N-POM contents were significantly higher under NT than under CT over the entire growing season.…”

“…It provides a substrate for microorganisms, and has been associated with changes in the soil mineralisable organic nitrogen pool (Hassink, 1995a). Many studies have used the POM fraction as an index of labile SOM status, and it is recognised as a potential indicator of soil quality changes in the short term (Marriot & Wander, 2006;Yoo & Wander, 2008;Sequeira et al, 2010). Some authors indicate POM to accumulate at the soil surface when tillage is reduced (Wander et al, 1998;Álvaro-Fuentes et al, 2008) and when cropping intensity is increased (Sainju et al, 2006a).…”

Effects of long-term use of different farming systems on some physical, chemical and microbiological parameters of soil quality

“…POM plays an important role in aggregate formation in soils and temporarily provides easily available nutrients for microorganisms and plants. Many researchers have used the POM fraction as an indicator of OM status in soil and recognised POM as a potential indicator of changes in soil quality in the short term (Sequeira et al, 2010;Yoo and Wander, 2008).…”

Soil Quality of Die off and Die Back Mangrove Grown at Al-Jubail Area (Saudi Arabia) of the Arabian Gulf

“…This inferred that for a given amount of organic C in soil, proportionally more C would be assimilated through microbial biomass with the high qCO 2 and the soils under stress would accumulate less C over time [6] . A high qCO 2 was reported in less productive soil compared to more productive soil [12] and continuous loss of CO 2 from soil may indicate ecosystem inefficiency, that is, energy loss from the soil system [8] . High ecosystem respiration, qCO 2 in soil may often result from stress and disturbance factors.…”