Equivalent Mass Basis Research Articles

Variability in carbon sequestration potential in no-till soil landscapes of southern Ontario

Soil organic carbon (SOC) in Canadian agricultural soils plays an important role in the global cycle of C, and management can influence its fate. Although the scientific literature suggests that practicing no-till (NT) can sequester C, this is not always the case. Furthermore, there are many other factors including climate, management history, soil type and soil landscape processes that may affect the dynamics of SOC under NT. We measured the changes in SOC under NT in southern Ontario, at varying positions in the landscape in Gleyic and Orthic Luvisols at the end of a 15-year-period. Soil cores taken to depths beyond the solum, were segmented with depth, and total SOC was determined for each segment on an equivalent mass basis. When the entire soil column was considered, there was a loss of SOC in more profiles than there were gains. Furthermore, the erosion/deposition history at each landscape position appeared to influence the dynamics of SOC. In depression areas where A p horizons were greater than 27 cm thick due to a history of soil deposition from upslope and local hydrology, there was a loss of total SOC after 15 years of NT. While where the A p thickness was less than 27 cm, there were 18 profiles with SOC gains and 15 with net losses. Multiple linear regression analysis revealed that the change in SOC after 15 years was negatively related to the initial total SOC content and positively related to mass of clay. The results of this study suggest that landscape position and erosion/deposition history play a significant role in the ability of NT soils to sequester SOC. Interpretations of long-term SOC monitoring studies must take into account the location of samples within fields if useful information is to be gained on C dynamics in agricultural soils.

Impacts of tillage practices on total, loose- and occluded-particulate, and humified organic carbon fractions in soils within a field in southern Ontario

The effects of no-tillage (NT) and moldboard plowing (MP) on the distribution and storage of soil organic carbon (SOC) and different C fractions were determined along a transect on a private farm in southern Ontario, Canada, where a paired NT and MP strip traversing three soil series had been in existence for 19 yr. Soil samples were collected to a depth of 60 cm in seven increments. SOC was determined in each sample and for the top 30 cm, the organic carbon was fractionated into loose-, occluded-particulate organic matter (loose-POM and occluded-POM) and humified fraction (HF). After 19 yr, soils under NT contained significantly (P < 0.05) more SOC than soils under MP on both an equivalent depth basis and an equivalent mass basis. Greater concentrations of loose- and occluded-POM were found in NT than MP surface soils (0-10 cm). MP favored higher loose-POM contents than NT practices at a depth of 10-20 cm. The HF fraction accounted for most of the increase in SOC in the Huron and Brady soils, whereas the occluded POM accounted for more of the increase in the Fox soil. Our results indicate that the extent of SOC sequestration under NT is strongly dependent on soil type and cropping history. Key words: Tillage practices, soil organic carbon, C fraction, C sequestration

Rotation and tillage effects on soil organic carbon sequestration in a typic Hapludalf in Southern Ontario

Increased use of conservation tillage is being considered as a way to sequester atmospheric C in the soil. However, little information exists on the effect of rotation and its interaction with tillage on soil organic carbon (SOC). A research trial with combinations of rotations and tillage treatments was sampled 20 years after its establishment to assess the effects on SOC sequestration in a typic Hapludalf in southern Ontario, Canada. The cropping treatments included continuous corn ( zea mays L.), six rotations comprised of 2 years of corn following 2 years of another crop or crop sequence, and continuous alfalfa ( Medicago sativa L.). Each rotation was split into either fall moldboard plow (MP) or fall chisel plow (CP) treatments. Continuous alfalfa was plowed and replanted every 4 years. Soil samples were taken incrementally to a depth of 40 cm and SOC and bulk density determined. The average SOC concentration (0–40 cm) was greatest in continuous alfalfa (18.0 g C kg −1). The treatments of soybean (Glycine max L. Merr. )+ winter wheat ( Triticum aestivum L.) or barley+barley ( Trifolium pratense L.) (interseeded with red clover) followed by 2 years of corn had higher SOC concentrations (17.2–17.3 g C kg −1) than continuous corn and the treatments of 2 years of corn following 2 years of alfalfa or soybean (16.4–16.5 g C kg −1). The rotation of 2 years of barley followed by 2 years of corn had the lowest SOC concentrations (15.2 g C kg −1). On an equivalent mass basis, the rotations of soybean+ winter wheat or barley+barley (underseeded with red clover) followed by 2 years of corn, had 2–9 Mg ha −1 more C than the other corn-based rotations. Including red clover in the winter wheat seemed to accelerate the rate of C mineralization compared to winter wheat without red clover; whereas interseeding red clover with barley increased SOC contents compared to excluding red clover in the barley rotation. More SOC was found in the top 10 cm and less in the 10–20 cm depth of the CP than in the MP soils. However, the CP did not increase the SOC content (0–20 cm) above that of MP indicating that this form of reduced tillage did not increase C sequestration in any of the rotations on this soil.

Tillage Impacts on Depth Distribution of Total and Particulate Organic Matter in Three Illinois Soils

AbstractThe benefits of no‐tillage (NT) practices to soil organic matter (SOM) are inconsistent in fine‐textured, poorly drained soils. Tillage impacts on SOM were investigated in central Illinois, assuming particulate organic matter (POM) would accumulate where SOM aggraded. Soils were collected in 1994 and 1995 from a trial established in 1985 at Perry and Monmouth (somewhat poorly drained Aquic Argiudoll silt loams), and DeKalb (a poorly drained Typic Haplaquoll silty clay loam). In general, NT practices increased SOM‐C and POM‐C contents 25 and 70% compared with conventional till (CT) at the soil surface (0–5 cm). This was at the expense of C at depth (5–17.5 cm), which decreased by 4 and 18%, respectively. Tillage effects varied among sites. No‐till increased SOM C and POM C more than 30 and 100%, respectively, in the top 5 cm of the two silt loams. In the silty clay loam, NT reduced SOM C 14% in the 5‐ to 17.5‐cm depth and POM C more than 20% in the 5‐ to 30‐cm depth. Bulk density was greater under NT than CT at the DeKalb (0–17.5 cm) and Monmouth sites (0–5 cm). No‐till only increased C and N sequestration, assessed on an equivalent mass basis, at Monmouth. Accumulation of POM in the surface depth of the NT silt loams may have improved soil quality in those erosion‐prone soils. Reduced POM contents in the NT silty clay loam may reflect SOM degradation. The high clay and organic matter content and low bulk density of the DeKalb soil may have contributed to the atypical effect of NT practices on SOM at that site.

Growth modulation and proteoglycan turnover in cultured mesangial cells.

Proliferation of mesangial cells is a common feature of renal disease, and conditioned media from glomerular epithelial and endothelial cells have been found to contain heparin-like molecules that suppress proliferation of rat mesangial cells (RMC). We have partially characterized the glycosaminoglycans that are labeled with 35SO4(2-) by RMC in culture at early passage and examined their ability to inhibit mitogenic stimulation of the cells. Four chondroitin/dermatan sulfate proteoglycans (CS/DSPG) were identified, the largest and smallest of which (Kd of 0.04 and 0.26 on Superose 6) were retained in the cell layer while the other two (Kd = 0.17 and 0.22) were secreted into the medium. Heparan sulfate proteoglycans (HSPG) with Kd values of 0.09, 0.13, and 0.39 were minor components of the cell layer, while a single heparan sulfate (Kd = 0.17) was recovered from the medium. After 16 h of labeling in serum-free medium, about 60% of macromolecular 35S was cell-associated and 40% was in the medium. Cell-associated label consisted of 7% CS/DSPG, 9% HSPG, and 84% free glycosaminoglycan chains (mostly CS/DS), whereas the medium contained 52% CS/DSPG, 17% HSPG, and approximately equal amounts of free HS and CS/DS chains. Bovine lung heparin (1 microgram/ml) decreased by 45% the incorporation of [3H]-thymidine into DNA after release of serum-starved RMC from growth arrest. Heparin acted prior to the G1/S interface; arrest of the cells in early S phase with aphidicolin abrogated the heparin response. The endogenous HSPGs had a slight antimitogenic effect on the RMC, but heparan sulfate chains from both the medium and cell layer had a potent effect. On an equivalent mass basis, only the free glycosaminoglycan chains were more potent than heparin in this regard, decreasing thymidine incorporation by over 90% when present at 1 microgram/ml. These results demonstrate that heparan sulfate glycosaminoglycans derived from mesangial proteoglycans are potential negative autocrine growth regulators. Proteoglycan metabolism releases these soluble heparan sulfate chains, determining the level of this activity.