Meng-Yang You

Nitrous oxide emissions from Mollisols as affected by long-term applications of organic amendments and chemical fertilizers

A field experiment was conducted to evaluate the influences of long-term applications of organic amendments and chemical fertilizers on nitrous oxide (N2O) emissions from Mollisols in northeast China and to relate soil N2O fluxes to soil moisture and temperature. A closed-chamber method was used to determine soil N2O flux during the maize growing season in 2011. In the entire maize growing period, cumulative N2O emissions were significantly (all P<0.05) increased by 66, 86 and 83% under the applications of 4.5 Mg ha(-1) maize straw combined with NPK, 7.5 and 22.5 Mg ha(-1) pig manure combined with NPK, respectively, compared with the control (0.64±0.01 kg N2O-N ha(-1)), whereas NPK fertilizer alone and 2.25 Mg ha(-1) maize straw combined with NPK had no remarkable influences (P>0.05). Nonetheless, even increasing nitrogen inputs, the cumulative microbial N2O emission over 126 days had an upper threshold around 1.2 kg N2O-N ha(-1). Approximately 25-44% of N2O was emitted from the applied organic amendments, and the emission factor (EF) of applied organic amendments as N2O based on 126 days was between 0.07 and 1.52%, higher than NPK fertilizer-induced EF (0.03%). Soil temperature explained 38-96% of the seasonal variation in soil N2O fluxes using exponential models, with a Q10 of 2.01-3.48. Our results suggest that the influences of organic amendments on soil N2O emissions from Mollisols primarily vary with the type of the applied organic amendments, whereas great nitrogen inputs at maximum asymptotically double baseline cumulative emissions.

Change in soil organic carbon between 1981 and 2011 in croplands of Heilongjiang Province, northeast China.

BACKGROUND Soil organic carbon (SOC) is fundamental for mitigating climate change as well as improving soil fertility. Databases of SOC obtained from soil surveys in 1981 and 2011 were used to assess SOC change (0-20 cm) in croplands of Heilongjiang Province in northeast China. Three counties (Lindian, Hailun and Baoqing) were selected as typical croplands representing major soil types and land use types in the region. RESULTS The changes in SOC density (SOCD) between 1981 and 2001 were -6.6, -14.7 and 5.7 Mg C ha(-1) in Lindian, Hailun and Baoqing Counties respectively. The total SOC storage (SOCS) changes were estimated to be -11.3, -19.1 and 16.5% of those in 1981 in the respective counties. The results showed 22-550% increases in SOCS in rice (Oryza sativa L.) paddies in the three counties, but 28-33% decreases in dry cropland in Lindian and Hailun Counties. In addition, an increase of 11.4 Mg C ha(-1) in SOCD was observed in state-owned farms (P < 0.05), whereas no significant change was observed in family-owned farms. CONCLUSION Soil C:N ratio and initial SOCD related to soil groups were important determinants of SOCD changes. Land use and residue returning greatly affected SOC changes in the study region. To increase the topsoil SOCD, the results suggest the conversion of dry croplands to rice paddies and returning of crop residue to soils.

Increase in soil organic carbon in a Mollisol following simulated initial development from parent material

Better understanding of the effects of land use and agricultural management on organic carbon (C) sequestration is needed to optimize the restoration of fertility in degraded soil, maintain agricultural sustainability and mitigate emissions of greenhouse gases with C sequestration. Most current studies of C sequestration focus on mature soil, whereas there has been little research on soil development from C-poor parent material. The aim of this study was to assess soil organic carbon (SOC) stocks and C sequestration rates during the early stages of development of a Mollisol from parent material under different types of vegetation, fertilizer application regimes and organic matter inputs, and to compare the results with C sequestration of a mature Mollisol under similar management. Carbon stocks were recorded from 2004 to 2012 in the parent material of a Mollisol under natural fallow (NatF), alfalfa (Medicago sativa L.) (Alfa) or soya beans (Glycine max (Merrill.) L.) and maize (Zea mays L.) (S–M) rotations with and without fertilizer application and crop residues returned or removed at harvest. There was a positive non-linear relation between C inputs and SOC stocks; increases in SOC stocks decreased with larger additions of C. After 8 years of treatments, the SOC stocks at 0–20-cm depth had increased in the order S–M + fertilizer + all residues returned (61%) > Alfa (60%) > S–M + fertilizer + part of residues returned (50%) > NatF (30%) > S–M + fertilizer without residue return (17%) > S–M without fertilizer or residue return (7%). These increases in SOC stocks corresponded to annual C sequestration rates of 0.02–0.83 Mg C ha−1 year−1. In contrast, SOC stocks in the 0–20-cm layer of the mature Mollisol changed little under similar treatments in a wheat (Triticum aestivum L.)–maize–soya bean rotation. Our results have practical implications for how vegetation and agricultural practices could be used to optimize soil restoration and C sequestration in a temperate continental monsoon climate. Highlights What management practices and vegetation lead to carbon sequestration during soil development? Use of a subsoil (parent material) to study soil development. Carbon stocks increased as much in alfalfa as in soya bean–maize rotations with residue return. Perennial legume systems sequester carbon comparable to annual systems with larger carbon inputs.

Changes in Soil Organic Carbon and Carbon Fractions Under Different Land Use and Management Practices After Development From Parent Material of Mollisols

Abstract Soil organic carbon (SOC) is important to soil nutrient status in agroecosystems. Some of the soils of the Northeast of China, noted for their high SOC content, suffer from serious soil erosion to the point of having the parent material exposed or near the surface, which has raised concerns for food security. The Chinese Mollisols were derived from loamy Quaternary loess that developed from parent material. To effectively restore parent material to productive soils, information on the effects of land use/management practices on SOC concentration and C fractions in loess parent material of Chinese Mollisols is needed. The main objective of this study was to investigate the changes in C sequestration and C density fractions by physical and chemical fractionation (humic substances) occurring in the process of soil development from parent material under different management practices and land use. Six treatments were imposed in plots of loess parent material in a 5-year experiment: (1) natural fallow without weed control; (2) alfalfa; (3) soybean-maize rotation (S-M), straw of unfertilized maize removed; (4) S-M, straw of chemically fertilized maize removed; (5) S-M, straw of chemically fertilized maize and dried soybean powder incorporated; (6) S-M, biomass, including grain, of chemically fertilized maize incorporated. The SOC content increased by 15% to 77% depending on treatments. In the process of soil development, the C fractions of the parent material changed rapidly. The heavy fraction C pool accounted for a larger proportion of total SOC (78%–89%) than both the free light fraction (2.1%–10.2%) and the occluded light fraction (1.3%–12.9%) pools. The occluded light fraction was more sensitive than the free light fraction as indicator of soil C changes because of different land use and management practices. Humin accounted for a larger proportion (29.9%–54.7%) of SOC than fulvic acid (18.0%–34.4%), which was larger than the humic acid fraction (11.8%–14.8%). Our results indicate that SOC increase in loess parent material depends on types and amounts of organic matter inputs. The treatments, in which aboveground crop biomass and grain were incorporated, contributed more to C sequestration, distributions of density fraction, and humic substances than the treatments without organic matter. Management practices maximizing biomass inputs are recommended to restore SOC in degraded Chinese Mollisols in order to restore their fertility.

Soil CO2 Emissions as Affected by 20-Year Continuous Cropping in Mollisols

Long-term continuous cropping of soybean (Glycine max), spring wheat (Triticum aesativum) and maize (Zea mays) is widely practiced by local farmers in northeast China. A field experiment (started in 1991) was used to investigate the differences in soil carbon dioxide (CO2) emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO 2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems (P>0.05). However, significant differences in CO 2 emissions from soils were observed among the three cropping systems (P continuous wheat ((629±22) g CO2 m -2 )>continuous soybean ((474±30) g CO2 m -2 ). Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature (T, °C) and water-filled pore space (W, %), log(f)=a+bT log(W), was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.

Removal of ciprofloxacin from aqueous solutions by ionic surfactant-modified carbon nanotubes

Ionic surfactants may impact removal efficiency of organic contaminants from aqueous solution, but research regarding the adsorption mechanisms on surfactant-modified carbon nanotubes (CNTs) was limited. In this study, three multi-walled and one single-walled CNTs were used as adsorbents to investigate the adsorption behavior and mechanisms of ciprofloxacin (CIP) on CNTs modified by ionic surfactants (cationic CTAB (Cetyltrimethylamnonium bromide) or anionic SDS (Sodium dodecyl sulfate)). More than 80% (82-88%) of the total removed CIP on CTAB-modified CNTs occurred within the first 6 h, much higher than that on SDS-modified CNTs (57-78%). Modeling adsorption kinetics demonstrated that CIP adsorption on surfactant-modified CNTs was controlled by multiple and faster processes, and both external mass transfer and intraparticle diffusion are limiting factors. Relative to SDS, CTAB was significantly (P < 0.001) concentration-dependent in suppressing CIP removal. Besides, the increase in 1/n values of Freundlich model with increasing CTAB concentration suggested that CTAB could be a stronger competitor for CIP adsorption. Hydrophobic interactions predominated zwitterionic CIP adsorption on all CNTs tested, while electrostatic interactions could help control ionizable CIP adsorption on surfactant-modified CNTs depending upon pH. CIP adsorption on modified SWCNTs significantly declined with increasing ionic strength from 1 mM to 100 mM relative to those multi-walled CNTs because the more favorable aggregation of SWCNTs reduced the CIP adsorption, irrespective of which surfactant was added. Significant desorption hysteresis of adsorbed CIP released by SDS and water was observed, but not by CTAB, by which 32.6-54.4% of adsorbed CIP were removed. For SDS-modified CNTs, the mean release ratio (RR) followed an order of MWCNTs (0.075) > MHCNTs (0.058) > SWCNTs (0.057) > MCCNTs (0.049), significantly (P < 0.001) lower than CTAB-CNTs (0.37-0.56). It can be predicted that the tested surfactants co-existing with CNTs depress removal efficiency of diverse contaminants similar to CIP in aqueous systems.

Redistribution of different organic carbon fractions in the soil profile of a typical Chinese Mollisol with land-use change

ABSTRACT Soil organic carbon (SOC) content depends significantly upon changes in land use and vegetation cover. This study aimed to examine the redistribution of whole soil OC, water-soluble OC (WSOC), and different density-separated OC fractions in soil profiles of 0–100 cm under different land uses and to elaborate the mechanism of C sequestration in response to the land use change. The land use types include maize plots with or without chemical fertilizer application (i.e., Maize-nitrogen, phosphorus, and potassium (NPK) and Maize-NF plots), plots with vegetation removed (No Vegetation), plots with grass (Grass), and alfalfa plant (Alfalfa). These plots used to be maize cropping system with NPK fertilizer for many years before 2003. Significant difference in SOC content generally occurred in soil layers of 0–40 cm among the different plots after 11 years of land-use change. Long-term continuous maize planting decreased SOC content; the significant SOC decrease occurred in Maize plot in the range of 9.3–23.4% for different soil layers compared with the initial soil sampled in 2003. In addition, SOC in Maize plot decreased by 3.6% and 8.5% at top two soil layers, respectively, in comparison with No Vegetation plot. The similar reduction of OC was observed in heavy OC fractions. The calculated sensitivity index for OC decreased in the order of light fraction > water-soluble fraction > the whole soil > heavy fraction. Therefore, the young and labile carbon fractions are much sensitive to land use change relative to the old and recalcitrant carbon fractions. This study indicated that land use changes led to a redistribution of SOC in soil profile, particularly at top soil layers, and conversion from arable land to natural grass cover or nitrogen-fixation plant cultivation such as alfalfa led to the enrichment of SOC at different depths of soil profile.