• Authors:
    • Wang, J.
    • Mei, X.
    • Zhang, Y.
    • Yan, C.
    • Chen, B.
    • Liu, E.
  • Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
  • Volume: 79
  • Issue: 2
  • Year: 2015
  • Summary: Tillage practices affect soil organic carbon (SOC) pools, which in turn influence soil ecosystem processes. In this study we measured the effects of long-term conventional tillage (CT) and no-till (NT) practices on SOC and its fraction over the winter wheat growing season in surface and subsurface soils. Soil samples were taken during five physiological stages of winter wheat growth to a depth of 60 cm from the long-term (19 yr) experimental station on Loess Plateau in China. While the SOC content increased slowly in the surface soils during winter wheat growth with the NT treatment, it showed less fluctuation with the CT treatment. On average, NT treatment resulted in 82 and 53% higher SOC content in depth of 0 to 5 and 5 to 10 cm than CT treatment (P < 0.05). However, seasonal variations in microbial biomass carbon (MBC) and particulate organic carbon (POC) were similar under NT and CT, and showed maximum values in before-winter anthesis stage. The dissolved organic carbon (DOC) trend was highest before sowing, decreased before the winter and jointed stages, and increased again during the anthesis stage. Particulate organic carbon, MBC, and DOC were all significantly higher with NT than with CT in the upper 10 cm. Soil depth affected SOC and its fraction which decreased from surface to subsurface soil. The POC, MBC, and DOC were highly correlated with the SOC. This study demonstrated that measurements of the effect of tillage practices on SOC based on SOC fractions should include both seasonal changes and profile distribution.
  • Authors:
    • Yan, Z.
    • Cao, C.
    • Guo, S.
    • Jia, J.
    • Sun, L.
    • He, Y.
    • Peng, Q.
    • Qi, Y.
    • Dong, Y.
    • Liu, X.
    • Liu, X.
  • Source: Soil and Tillage Research
  • Volume: 151
  • Year: 2015
  • Summary: The Chinese steppe is undergoing a drastic increase in nitrogen (N) deposition, and the precipitation in this region is predicted to increase. However, the response of soil N2O emissions to the coupling changes of precipitation and N deposition in grassland ecosystem has been seldom discussed. A manipulative field experiment was conducted to investigate the individual and interactive effects of precipitation increase and N deposition on soil N2O efflux in semi-arid temperate grassland in Inner Mongolia during the growing seasons of 2010 and 2011.The treatments included four N addition levels [20gNm-2y-1 (N20), 10gNm-2y-1 (N10), 5gNm-2y-1 (N5), and a zero-N control (CK)] and two water application levels [natural precipitation for dry (D) and 15% increase of long-term mean annual precipitation for wet (W) treatments]. Results indicated that N and water addition both significantly increased soil N2O effluxes (P<0.01). The maximum N2O emissions were observed within 2-3 days after N addition to all treatments, and the N2O effluxes in W treatments were generally higher than in D treatments for the same N input level. For the treatments without N inputs, the N2O emission peak of WCK was 9.8% higher than DCK in 2010. The effect of water addition on N2O emission was more evident when more N fertilizer was applied. For the high N input treatments, the maximum N2O emission of WN20 treatment was 222.6% higher than DN20 in 2010. The changes in N and water availabilities accounted for 91.3% (2010) and 75.6% (2011) of the N2O cumulative efflux variation among different treatments (P<0.01). The N2O effluxes were significantly affected by the interactive effect between N and water in 2010 and 2011 (P<0.05). Significant interannual variability in the cumulative N2O emissions was observed, the cumulative N2O emissions in 2011 were significantly lower than those in 2010 even though the summer of 2011 experienced higher rainfall (P<0.01). Temperature also significantly influenced soil N2O emission apart from the effects of water and N. The temperature change accounted for 41.3% (W) to 47.2% (D) of the temporal variations in N2O emission during the relatively dry 2010. The combined changes in soil moisture, NH4 +-N, and temperature accounted for 43.1% (D) to 54.5% (W) of the temporal variations in N2O emission in the relatively wet year of 2011.
  • Authors:
    • Zhang, Y.
    • Xu, Z.
    • Li, B.
    • Cai, J.
    • Creamer, C. A.
    • Dungait, J. A. J.
    • Wang, R.
    • Ma, Y.
    • Jiang, Y.
  • Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
  • Volume: 79
  • Issue: 2
  • Year: 2015
  • Summary: Anthropogenic-driven changes in N and water availability are two of the most important factors determining soil C and N turnover in temperate grassland ecosystems. To gain insight into changes in soil aggregation and C and N dynamics in response to N and water addition, we collected soil samples from a field study conducted for 9 yr in a semiarid steppe grassland in Inner Mongolia, China. Three aggregate size classes (microaggregates, 2000 μm) were isolated and analyzed for their mass proportions, soil organic C (SOC), total N (TN), total extractable inorganic N (TIN), and stable isotope ratio of 13C relative to 12C (δ13C) and stable isotope ratio of 15N relative to 14N (δ15N) values. Water addition on average increased large macroaggregates by 33% and decreased microaggregates by 42%. Nitrogen and water addition interacted significantly and increased TIN concentration but had no impact on SOC or TN. Soil organic C was negatively correlated with δ13C values of large and small macroaggregates under ambient precipitation and within all soil aggregates under water addition. Significant positive correlations between TIN and δ15N values were detected for large macroaggregates and microaggregates under ambient precipitation. Our results suggest that water addition accelerated plant residue incorporation into soil organic matter (SOM) (indicated by depleted 13C values) while N addition potentially increased gaseous N losses (suggested by 15N enrichment without changing soil C and N concentrations). Water, but not N, improved soil structure in this semiarid grassland. Our study provides new insights for using natural abundance 13C and 15N to better understand the sensitivity of SOM within different soil particles to coupled N-water changes under global change scenarios.
  • Authors:
    • Fan, M.
    • Zhang, F.
    • Yan, Y.
    • Six, J.
    • Lee, J.
    • Cao, J.
  • Source: European Journal of Soil Biology
  • Volume: 68
  • Year: 2015
  • Summary: In China, considerable cropland previously under grain production has been rapidly converted to greenhouse vegetable production by farmers since 1980s. Vegetable crops generally require higher nitrogen (N) inputs from manure amendments and more frequent tillage and irrigation operations compared to grain crops. Here, we compared potential denitrification-derived N2O emissions across the soil profile (0-90cm depth) between grain and greenhouse vegetable fields. Denitrification enzyme activity (DEA) was assessed in the top 0-15cm soil layer. Soil samples from five wheat (Triticum aestivum L.) - maize (Zea mays L.) fields, paired with adjacent vegetable greenhouse fields, were collected across typical vegetable production regions. Conversion from the grain fields to the greenhouse vegetable fields led to greater potential denitrification-derived N2O emissions in the 0-15 and 15-30cm depths, respectively, with 4 and 3 times higher cumulative emissions over the 10-day incubation. Continuous manure amendments and chemical N input increased water extractable organic carbon and nitrate concentrations, which significantly enhanced potential denitrification-derived N2O production in the 0-30cm soil depth of vegetable crop fields. The differences in microbial community for the two cropping systems did not seem to affect the surface N2O production potential since denitrification enzyme activity were not significantly different between the two production systems. There was a small to negligible potential N2O flux in 30-90cm soil depths for both production systems because of limited carbon availability and microbial activity. Managing surface labile carbon and mineral N pool may be critical in reducing regional N2O emissions in China's greenhouse vegetable production systems.
  • Authors:
    • Gao, R.
    • Cao, F. Q.
    • Dan, L.
  • Source: CLIMATIC CHANGE
  • Volume: 129
  • Issue: 3-4
  • Year: 2015
  • Summary: The Atmospheric-Vegetation Interaction Model (AVIM) is coupled with a Regional Integrated Environment Modeling System (RIEMS) to improve the regional simulation of climate variables. A case study in 1998 is implemented to study the improvement mechanism through land-air interaction in East Asia, especially in Asian summer monsoon regions. The coupled model reduces the warming bias in July in East China through the surface heat fluxes changes. Compared to the original model of RIEMS, the strong precipitation of eastern China in July is weakened by coupling of the interactive vegetation. The surface heat flux in uncoupled model is remarkably overestimated in these regions, and the enhanced heating from land surface, particularly with latent heat flux in July, will produce the overestimated temperature and precipitation in East China. Through coupling AVIM with RIEMS, the simulated area-averaged latent heat flux of two key regions decreases (e.g. from 132.36 to 103.13 W/m(2) over the region 1 between 105-125A degrees E and 20-40A degrees N) in July, which makes the overestimated temperature and precipitation declined, respectively.
  • Authors:
    • Mahmood, R.
    • Han, Y. H.
    • Yang, Q.
    • Ma, Z. G.
    • Fan, X. G.
  • Source: CLIMATIC CHANGE
  • Volume: 129
  • Issue: 3-4
  • Year: 2015
  • Summary: Afforestation efforts in China resulted in significant changes in vegetation coverage over the Loess Plateau during 2001-2009. While regional climate conditions dominate the distribution of major vegetation types, human activities, primarily afforestation/reforestation and the resultant land use/land cover (LULC) changes (LULCC) and their impacts, are the focus of this study. A new attribution method was developed and applied to observed data for investigating the interrelationships between climate variation and LULCC. Regional climate (temperature and precipitation) changes are attributed to climate variation and LULCC; LULCC is attributed to climate variation and human activities. Climate attribution analysis indicated a larger contribution ratio (based on comparison of standard deviations of each contributing factor-induced climate changes and that of total change) from climate variation than from LULCC (0.95 from climate variation vs. 0.35 from LULCC) for variations in temperature. Impacts on precipitation indicated more spatial variations than those on temperature. The spatial variation of LULCC impacts on precipitation implied that human activities might have larger impacts on precipitation in the region's arid north than in its humid south. Using both leaf area index (LAI) and areal coverage of each of the major land types, LULCC attribution analysis suggested that LULCC observed in the 2000s resulted primarily from human activities rather than climate variations (0.99 contribution ratio from human activities vs. 0.26 from climate variation).
  • Authors:
    • Zheng, Z. Y.
    • Mahmood, R.
    • Han, Y. H.
    • Yang, Q.
    • Ma, Z. G.
    • Fan, X. G.
  • Source: CLIMATIC CHANGE
  • Volume: 129
  • Issue: 3-4
  • Year: 2015
  • Summary: Adverse environmental impacts from deforestation are a growing area of concern in climate change discussions. The Chinese government has implemented a series of policies, such as the Grain for Green Project, in an attempt to mitigate the impacts. This study takes a regional perspective to report land use/land cover changes over the Loess Plateau region from 2001 to 2009. MODIS data were used in analyzing both the conversions among and the resulting changes in different land types. Government statistical census data and observed climate data were also incorporated in the analysis. A general consistency is shown in both remotely sensed and census data. With the implementation of various projects, including the Grain for Green Project, the total areas covered by grassland, cropland, and forests have increased by 19.2 % (6.05 x 10(4) km(2)), 33.7 % (5.80 x 10(4) km(2)), and 19.6 % (3.08 x 10(4) km(2)), respectively, during the 9-year period. While climatic conditions, particularly annual precipitation totals, usually dominate the distribution of vegetation, it is found that socioeconomic polices and human activities contribute to the increase in overall greenness and to vegetation growth (e.g., LAI increased by 16.8 % (0.10) overall). However, the feedback of land use/land cover to regional climate is complicated and cannot be easily distinguished from natural climate variations based on short-term observational data alone. To better isolate the effects, further analysis and modeling studies are suggested.
  • Authors:
    • Zhang, F. S.
    • Chen, X. P.
    • Christie, P.
    • Cui, Z. L.
    • Meng, Q. F.
    • Ju, X. T.
    • Gao, B.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 203
  • Year: 2015
  • Summary: The large consumption of groundwater for irrigating winter wheat has resulted in a continuous decline in the groundwater table on the North China Plain in recent decades. Alternative cropping systems have been proposed to substitute for the conventional winter wheat-summer maize rotation system for the sustainable use of groundwater in the future. However, the impact of these cropping systems on net global warming potential (net GWP), and greenhouse gas emissions on the basis of per unit of yield (greenhouse gas intensity, GHGI) is poorly documented. Measurements of greenhouse gases were conducted over a four-year period to gain insight into net GWP and GHGI on a crop rotation scale based on an ongoing long-term field experiment on the North China Plain. The cropping systems investigated include one conventional winter wheat-summer maize system (Chem. W/M) as the control and four alternative cropping systems, namely an optimized winter wheat-summer maize system (Opt. W/M), two winter wheat-summer maize (or soybean)-spring maize system with three crops in two years (W/M-M, W/S-M), and a single spring maize per year (M). Compared with the Chem. W/M control, the grain yields in Opt. W/M increased significantly by 19% while the net GWP, GHGI and fertilizer N decreased by 29%, 40% and 40%, respectively, but still consumed as much groundwater (264 mm yr(-1)) as Chem. W/M. In the two-year rotation cycle fertilizer N, groundwater use, net GWP and GHGI in W/M-M, W/S-M and M declined by 56-70%, 43-63%, 50-58% and 30-50%, respectively, compared to Chem. W/M. Moreover, these cropping systems consumed only 108-159 mm yr(-1) groundwater for irrigation, a value close to the theoretical value of 150 mm yr(-1) to avoid a continuing decline in the groundwater table in this region. However, W/S-M treatment had grain yield reductions of -23% and M treatment had -30%, and only W/M-M maintained grain yields relative to Chem. W/M. We, therefore recommend the W/M-M management package as a preferred option to maintain grain yields together with low GWP and GHGI while mitigating the decline in the groundwater table in areas with a high water deficit.
  • Authors:
    • Feng, S. F.
    • Zheng, Y. H.
    • Li, X.
    • Li, J.
    • Liu, H. T.
    • Jiang, G. M.
  • Source: SCIENCE BULLETIN
  • Volume: 60
  • Issue: 6
  • Year: 2015
  • Summary: Burning crop residues and excessive use of chemical fertilizers results in an enormous waste of biological resources, which further weakens the potential capacity of the agro-ecosystem as a carbon sink. To explore the potential of farmlands acting as a carbon sink without yield losses, we conducted an experiment on a temperate eco-farm in eastern rural China. Crop residues were applied to cattle feed, and the composted cattle manure was returned to cropland with a winter wheat and maize rotation. Four different proportions of fertilizers were designed: 100 % cattle manure, 100 % mineral nitrogen, 75 % cattle manure plus 25 % mineral nitrogen, and 50 % cattle manure plus 50 % mineral nitrogen. Crop yield and greenhouse gas (GHG) emissions were carefully calculated according to the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories 2006. Our results showed that replacing chemical fertilizer with organic manure significantly decreased the emission of GHGs. Yields of wheat and corn also increased as the soil fertility was improved by the application of cattle manure. Totally replacing chemical fertilizer with organic manure decreased GHG emissions, which reversed the agriculture ecosystem from a carbon source (+2.7 t CO2-eq. hm(-2) year(-1)) to a carbon sink (-8.8 t CO2-eq. hm(-2) year(-1)). Our findings provide useful insights for improving agricultural ecosystems under global change scenarios.
  • Authors:
    • Ren, S.
    • Gao, W.
    • Yang, J.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 151
  • Year: 2015
  • Summary: Integrating fertilizer nitrogen with organic materials was an important management strategy for sustainable agriculture production systems in most soils low in organic matter. A 33-year-old experiment with various fertilizations in a double cropping system rotated with winter wheat (Triticum aestivum L) and maize (Zea mays L) on a fluvo-aquic soil in Tianjin was evaluated. The six treatments used were control, N, NPK, NM, NS and NGM, representing various combinations of N, P, K, organic manure (M), straw (S) and green manure (GM) fertilizer applications. The specific objective of this study was to evaluate the long-term effects of combined use of organic materials and chemical fertilizer nitrogen on crop yields, soil organic carbon (SOC) and soil total nitrogen (TN).As a result, wheat and maize yields in the plot under the N treatment decreased with time, whereas the yields increased in the plot under NM treatment for both crops. The yields in NS and NGM treatments maintained a stable and higher level. Generally, both wheat and maize yields were significantly higher in NM and NPK than those in other treatments. The SOC and TN contents with all treatments showed an increasing trend with time. Compared with the N treatment, the average SOC and TN contents were 38.0 and 17.3%, 14.2 and 6.7%, and 12.9 and 6.1% larger, respectively, for NM, NPK, and NS. In addition, the SOC contents with the five treatments (N, NGM, NS, NPK and NM) increased by 25.5, 33.1, 42.1, 69.7 and 145.6%, respectively, by 2012; for TN they increased by 6.6, 17.8, 23.2, 35.5 and 57.5.5%, respectively, above the values obtained in 1979. TN contents were significantly correlated with SOC at each treatment (P<. 0.01). Soil C/N ratios were generally around 9 to 14 during cultivate time. The average soil C/N ratio in NM was significantly higher than those in other treatments, and the soil C/N ratios among the other four treatments were not significantly different.Overall, the results suggest that organic manure along with chemical N must be used to sustain the productivity and promote C and N sequestration of wheat-maize system in the fluvo-aquic soils of the Tianjin areas.