Lu-Jun Li

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.

Changes in labile soil organic matter fractions following land use change from monocropping to poplar-based agroforestry systems in a semiarid region of Northeast China

Labile fractions of soil organic matter (SOM) respond rapidly to land management practices and can be used as a sensitive indicator of changes in SOM. However, there is little information about the effect of agroforestry practices on labile SOM fractions in semiarid regions of China. In order to test the effects of land use change from monocropping to agroforestry systems on labile SOM fractions, we investigated soil microbial biomass C (MBC) and N, particulate organic matter C (POMC) and N (POMN), as well as total organic C (TOC) and total N (TN) in the 0- to 15-cm and the 15- to 30-cm layers in 4-year-old poplar-based agroforestry systems and adjoining monocropping systems with two different soil textures (sandy loam and sandy clay loam) in a semiarid region of Northeast China. Our results showed that poplar-based agroforestry practices affected soil MBC, POMC, and POMN, albeit there was no significant difference in TOC and TN. Agroforestry practices increased MBC, POMC, and POMN in sandy clay loam soils. However, in sandy loam soils, agroforestry practices only increased MBC and even decreased POMC and POMN at the 0- to 15-cm layer. Our results suggest that labile SOM fractions respond sensitively to poplar-based agroforestry practices and can provide early information about the changes in SOM in semiarid regions of Northeast China and highlight that the effects of agroforestry practices on labile SOM fractions vary with soil texture.

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.

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.

Accumulative Characteristics of Some Plant Species to Magnesium around a Magnesite Mine Area in Northeast China

The deposition of Mg-rich dust from magnesite calcination can lead to serious soil contamination. As an efficient remediation method, phytoremediation is often used to remove contaminants from the environment. However, no information is available on phytoremediation of Mg-contaminated soils. In this study, we determined the Mg concentrations in above- and belowground parts of six dominant plant species and soils (0–20 cm layer) beneath these plants in a magnesite mining region in Northeast China. Mg was enriched in leaves of all six species. Translocation factors (TF) of all six species were far greater than 1. Enrichment factors (EF) of Kochia scoparia, Cassia nomame, and Hordeum jubatum were 1.1, 1.1, and 1.0, respectively, while those of the other three species were not greater than 0.5. The results suggest that Kochia scoparia, Cassia nomame, and Hordeum jubatum are the potential Mg-accumulators, and could be used for remediation of Mg-contaminated soils.

Restoration Effect of Young Plantations on Magnesite Mine Spoil in Northeast China

We compared the effects of young plantations (4 to 5 years old) of two trees (Ulmus pumila and Robinia pseudoacacia (a legume)) and a shrub (Ziziphus jujube var. spinosa) on soil carbon and nutrient concentration, microbial biomass and their accretion during early phase of plantation establishment on mine spoils around a magnesite mine in Northeast China. There was a slight increase in soil total organic C (TOC), total N (TN), and a significant increase in microbial biomass C (MBC) and microbial biomass N (MBN) after restoration of 4 to 5 years for all the three species. Soil TOC, TN, MBC and MBN increased the most in R. pseudoacacia plantation than that in Z. jujube var. spinosa and U. pumila plantation. No significant differences in total P accretions were found among all treatments. These results indicated that soil quality was substantially improved during early phase of plantations establishment for all species. All the three species are promising for ecological restoration of mine spoils around magnesite mine regions, especially R. pseudoacacia has stronger impact on soil improvement.