Aggregate-associated Organic Carbon Research Articles

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (Dm) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in Dm of soil aggregate size distribution among tillage treatments, which suggested that Dm could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.

Spatial Prediction of Soil Aggregate Stability and Aggregate-Associated Organic Carbon Content at the Catchment Scale Using Geostatistical Techniques

The association of organic carbon with secondary particles (aggregates) results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km 2 to predict spatial variability of soil water-stable aggregates (WSA), mean weight diameter (MWD) of aggregates and organic carbon (OC) content in macro-(> 2 mm), meso-(1–2 mm), and micro-aggregate (< 1 mm) fractions, using geostatistical methods. One hundred and eleven soil samples were collected at the 0–10 cm depth and fractionated into macro-, meso-, and micro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates (9 g kg −1), followed by micro-aggregates (7 g kg −1), while the least OC content was found in macro-aggregates (3 g kg −1). Although a significant effect (P = 0.000) of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant effect (P = 0.073) on aggregate OC content. The coefficients of variation (CVs) for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable (CV = 71%). Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. The mean content of WSA ranged from 15% for macro-aggregates to 84% for micro-aggregates. Geostatistical analysis showed that the measured soil variables exhibited differences in their spatial patterns in both magnitude and space at each aggregate size fraction. The relative nugget variance for most aggregate-associated properties was lower than 45%. The range value for the variogram of water-stable aggregates was almost similar (about 3 km) for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about 6.5 km for meso-aggregates. Kriged maps of predicted WSA, OC and MWD for the three studied aggregate size fractions showed clear spatial patterns. However, a close spatial similarity (co-regionalization) was observed between WSA and MWD.

Production of Ni-Al 2O 3 powder coatings by hydrocarbon gas plasma process : S.V. Petrov, A.G. Saakov, Poroshkovaya Metallurgiya, No 11, 1990, 58–62, (In Russian)

Understanding organic carbon (OC) sequestration in aggregates and OC stability under different fertilization practices is of key importance in improving soil quality and crop productivity and in mitigating the causes of climate change. A long-term field experiment established in 1990 was used to assess the influence of organic and inorganic fertilizers on aggregate-associated OC and its mineralization and on the SOC stock at a soil depth of 0–20 cm under an intensive wheat-maize cropping system on Anthrosol in North China. The study involved three treatments: CK, control without fertilization; NPK, nitrogen (N), phosphorus (P) and potassium (K) fertilizers; MNPK, manure (M) combined with N, P and K fertilizers. Soil samples were collected and analyzed to determine the size distribution of aggregates, which were separated by dry sieving; the concentrations of OC and N in aggregates (> 2, 0.25–2 and < 0.25 mm) and bulk soils; and respiration from aggregates and bulk soils in the 0–10 and 10–20 cm layers after 21 years. Fertilization did not affect the size distribution of aggregates in the surface soil layer, but there was a significant change in the subsurface layer in response to manure addition. Application of NPK and MNPK significantly and evenly augmented OC and N sequestration in the three aggregate classes tested. However, the OC mineralization rate was substantially higher in micro- than in macro-aggregates. Application of NPK and MNPK considerably increased OC mineralization in both aggregates and bulk soils; MNPK yielded the highest values. OC mineralization rates in bulk soils were comparable among the three treatments for the surface layer, but they increased in the subsurface layer because of adding manure. Overall, soils treated for 21 years with NPK and MNPK showed increases in the OC pools in the top 20 cm of 7.42 and 22.83 Mg C ha− 1, respectively, compared with the control treatment, and had average sequestration rates of 353 and 1087 kg C ha− 1 yr− 1 respectively. Thus, appropriate application of NPK, alone or in combination with manure, can lead to improved OC sequestration by evenly augmenting aggregate-associated OC and providing the same degree of protection for OC in both macro-aggregates and micro-aggregates under a winter wheat-summer maize rotation on Anthrosol.