CK Plots Research Articles

Impacts of nitrogen management and organic matter application on nitrous oxide emissions and soil organic carbon from spring maize fields in the North China Plain

Soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions and carbon (C) sequestration are important processes for determining net greenhouse gas (GHG) emissions from maize fields. Farming management practices (FMPs) substantially affect crop productivity, soil organic carbon (SOC), and N2O emissions. However, relative knowledge is not sufficient, and further research is required for sustainable agriculture development. A multi-year experiment was performed on a spring maize field in the North China Plain (NCP) to quantify changes in SOC stocks, N2O emissions, and maize yields. Seven treatments were involved in the experiment, including no N fertilization (CK), farmers’ conventional N fertilization (FP), sole application of manure N (M), a combination of M and FP (MFP), FP combined with returned maize straw (SFP), fertilization with reduced synthetic N amount (RN), and fertilization with both reduced synthetic and manure N (RMN). The field measurements demonstrated that urea applications and returned maize straw increased N2O emission. The seasonal total N2O emissions under FP were significantly (P < 0.05) higher than those under CK by 176% to 222% and lower than those under SFP by 20% to 61% throughout the three maize growing seasons. The application of organic manure or maize straw enhanced SOC storage for the studied cropping system. The SOC stocks were relatively high in the plots that received applications of organic manure or maize straw, with the SOC stock of the M plot being significantly higher (P < 0.05) than that of the CK, FP, SFP, RN, and RMN plots in 2016 after eight years of manure amendments. The average net GHG emission from 2012 to 2014 was 203 kg CO2 equivalent ha−1 year−1 (i.e., a net GHG source) under FP. The other treatments converted the maize fields from net GHG sources to GHG sinks. By considering both the maize yields and net GHG emissions, RMN would be an optimal management option, although MFP, SFP, and RN also mitigated the GHG emissions and maintained the yields. Large variations were observed in the contributions of the SOC changes and N2O emissions to net GHG emissions among the treatments. The large variations demonstrate the need to consider both SOC changes and N2O emissions when evaluating the impacts of alternative FMPs on net GHG emissions.

Wind erosion changes induced by different grazing intensities in the desert steppe, Northern China

Desert steppes are fragile ecosystems, which generally suffer severe wind erosion hazards, especially when they experiencing external disturbances such as grazing. Therefore, the effects of grazing on the wind erosion process are very important for improving our understanding of the effects of the stocking rate on grassland degradation and enacting reasonable grazing strategies in grasslands. However, few studies have discussed the wind erosion changes induced by different grazing intensities thus far. Herein, a series of grazing experiments was carried out in a desert steppe in Urad Back Banner, Inner Mongolia. These experiments included 2 types of grasslands that are shrub dominated grassland (SDG) and grass dominated grassland (GDG). Each grassland type had 3 grazing rate treatments: no grazing as the control (CK), moderate grazing (MG), and heavy grazing (HZ). After the grazing experiments lasting for 4 years, sand traps were set in the grazing plots to detect the horizontal sand flux at different grazing intensities. In addition to the wind erosion observed, the vegetation and soil particles were also surveyed and sampled. Our results showed that the vegetation cover (VC) and aboveground biomass (AGB) in the MG and HG plots all had obvious differences compared to the CK plot, regardless of whether it was SDG or GDG. The soil particle analysis showed that the fractions of erodible particles (60–200 μm) in the MG and HG plots decreased significantly. In the GDG, the soil particles exhibited a coarsening trend from CK to HG plots for the sorting action of the wind. Suffering a grazing disturbance, the wind erosion in a desert steppe exhibited significant changes. For instance, in the SDG, the horizontal sand flux in the MG and HG plots were 1.78 and 2.06 times the sand flux in the CK plots, respectively, and, in the GDG, they were 17.86 and 56.53 times the flux in the CK plots, respectively. Except in the MG and HG plots of the GDG, the saltation height of sand was generally lower than 20 cm. In the SDG, the particle size of the entrained sand mainly ranged from 80 to 200 μm, and, in the GDG, it ranged from 80 to 300 μm. This finding also indicated the validity of Shao’s sand entrainment equation. We also found that particle size of saltating sand increased with their saltation height for the tough surface of the MG and HG plots in the GDG. Based on the different fractions of horizontal flux in different directions, we also discussed the threshold wind velocity for sand entrainment, and we confirmed that the threshold wind velocities for no grazing in SDG and GDG were approximately 16.5 m·s−1 and 15 m·s−1, respectively. Using our previous wind erosion model, we estimated the dust emission in the total desert steppe of China and found that different grazing scenarios would change the magnitude and distribution of dust emissions.

Effects of pelletized straw on soil nutrient properties in relation to crop yield

AbstractPoor soil‐residue contact from field‐chopped straw (CS) application restricts the efficient incorporation and rapid decomposition of crop residues in intensive cropping systems. Pelletized straw (PS), which has a high bulk density and relatively small size, can improve this contact, but its effect on soil fertility after incorporation is not well known. Therefore, a field experiment was conducted over four cropping seasons in Shandong Province, China, to evaluate the effects of corn CS and PS incorporation (6 t/ha) on soil organic carbon (SOC), available nitrogen (N), available phosphorus (P), available potassium (K), crop yields and economic benefits. Compared with the SOC and available N, P and K concentrations from 0 to 60 cm under the no straw incorporation (CK) treatment, the concentrations under the CS and PS treatments were higher but decreased gradually after treatment application. In the topsoil (0–20 cm) under the CS and PS treatments, these concentrations increased by 1.6% and 10.0%, by 18.5% and 25.8%, by 21.7% and 29.3%, and by 9.2% and 13.0%, respectively. Compared with the soil fertility in the CS plots, soil fertility in the PS plots improved, but significant differences were recorded only in the first season. The highest crop yield each season was obtained from the PS plots: wheat yields were 8.8% and 10.3% higher in the PS plots than those in the CS and CK plots, respectively, and corn yields were 2.8% and 16.9% higher, respectively. Furthermore, the net economic return averaged across 2 yr was 7.8% and 23.9% greater with the PS treatment than that with the CS and CK treatments, respectively. Thus, PS may constitute an efficient and economical approach for improving soil fertility and increasing crop yields in intensive cropping systems.

Effect of asymmetric warming on rice (Oryza sativa) growth characteristics and yield components under a free air temperature increase apparatus

Climate warming shows great diurnal variations with higher warming rate at nighttime, and consequently causes significant impacts on rice growth and grain yield. The objective of this study was to determine the effects of asymmetric warming (all-day warming, AW; daytime warming from 7:00 to 19:00, DW; and nighttime warming from 19:00 to 7:00, NW; and a control, CK) on rice growth characteristics andyield. Two bucket warming experiments were performed in Nanjing in Jiangsu Province, China under Free Air Temperature Increases (FATI) in 2013 and 2014.&lt; The daily mean temperatures in the rice canopy in the AW, DW and NW plots were 2.0°C, 1.1°C and 1.3°C higher, respectively, than those in the CK plots. Asymmetric warming reduced the maximum tillers and effective tillers in the order CK&gt;DW&gt;NW&gt;AW. In the AW, DW and NW treatments, the effective tillers were decreased by18.57%-37.77% in both years. Asymmetric warming also decreased plant height, the Absolute Growth Rate (AGR), the Soil and Plant Analyzer Development (SPAD) value, the Leaf Area Index (LAI) and the Net Photosynthetic Rate (Pn). The order of the plant height and Pn values were also in the order CK&gt;DW&gt;NW&gt;AW. The warming treatments affect the length of rice growth. The length from the transplanting date to the heading date was shortened by 3.5 days, 2.5 days and 3.0 days on average in the AW, DW and NW plots, respectively, in both years, while the length from the heading date to the maturation date did not show obvious changes. The aboveground biomass in the maturation stage declined by 13.38%, 3.56% and 6.22%, and the grain yield was decreased by 10.07%, 5.06% and 7.89% on average in the AW, DW and NW plots, respectively, in both years. There was a decreasing trend in the panicle number, grain number per panicle and grain filling rate, whereas irregular changes in the 1000-grain weight were observed in the warmed plots. Our results suggested that under the predicted climate warming, rice productivity would be further declined in the Yangtze River Basin.

Aboveground and belowground litter have equal contributions to soil CO2 emission: an evidence from a 4-year measurement in a subtropical forest

Changing quantity and quality of plant C input to soils under global change influences soil C cycling in terrestrial ecosystems. However, how soil CO2 emission responds to changes in C input remains poorly understood. A detritus input and removal experiment was conducted in a subtropical forest (Cunninghamia lanceolata) to investigate how aboveground and belowground litters affect soil respiration (RSoil). In this experiment, four treatments with three replicates were included, as follows: control (CK), litter removal (NL), root trenching (NR), and no C-input (i.e. litter removal combined with root trenching, NI). RSoil was measured for 4 years from 2011 to 2014. The mean annual CO2 effluxes in the NL, NR, and NI plots were lower (23.4%, 24.9%, and 38.8%, respectively) than those in the CK plots, suggesting that decreasing C input significantly decreased RSoil. Soil heterotrophic respiration (soil organic matter decomposed by microorganisms) accounted for 52.1% of RSoil, and aboveground recent litter decomposition and belowground autotrophic respiration (live roots and associated microorganism) contributed to 23.7% and 24.2% of RSoil, respectively. RSoil was significantly and positively correlated with soil temperature, but negatively correlated with volumetric soil moisture. The variation in RSoil was more explained by soil temperature than soil moisture, and the responses of RSoil to soil temperature and moisture were altered by C input manipulation. Annual RSoil rate was strongly and negatively related to the Gram-positive bacteria concentration and the ratio of Gram-positive to -negative bacteria. This study highlighted that aboveground recent leaf litter and belowground live roots and associated microbes had similar contributions to RSoil, and soil temperature and Gram-positive bacteria were the dominant factors controlling RSoil in a subtropical forest.

Subsoiling practices change root distribution and increase post-anthesis dry matter accumulation and yield in summer maize.

Subsoiling is an important management practice for improving maize yield, especially for maize planted at high plant density. However, the affected physiological processes have yet to be specifically identified. In this study, field experiments with two soil tillage (CK: no-tillage, SS: subsoiling) and three planting densities (low: 45000 plants ha−1, medium: 67500plants ha−1, and high: 90000 plants ha−1) were conducted from 2010 to 2012 at Xinxiang, Henan province. Yield, canopy function, and root system were investigated to determine the associated physiological processes for improving maize production affected by soil tillage and plant density. Subsoiling significantly increased the grain yield of the low-, medium-, and high-planting densities by 6.21%, 8.92%, and 10.09%, respectively. Yield increase in the SS plots was mainly attributed to greater post-anthesis DMA and improved grain filling compared to CK plots. Greater green leaf area, leaf net photosynthetic rate, FV/Fm and ΦPSII in the SS plots were mainly contributed to enhanced dry matter production post-anthesis. This is mainly because subsoiling increased density of root dry weight in deep soil and root bleeding sap amount due to decreased the bulk density of the 0–30 cm soil profile layer. Density of root dry weight at 10–50 cm depth with SS increased by 40.68%, 32.17%, and 20.14% at low, medium, and high planting densities compared to CK, respectively, while the root bleeding sap amount increased by 17.41%, 15.82%, and 20.91%. These results indicate that subsoiling could change the root distribution and improve soil layer environment for root growth, thus maintaining a higher canopy photosynthetic capacity post-anthesis and in turn promoting DMA and yield, particularly at higher planting densities.

Experimental Warming Effects on Soil Respiration, Nitrification, and Denitrification in a Winter Wheat-Soybean Rotation Cropland

ABSTRACTA field experiment was conducted to examine responses of soil respiration, nitrification, and denitrification to warming in a winter wheat (Triticum aestivum L.)–soybean (Glycine max (L.) Merr) rotation cropland. The results showed that seasonal variations in soil respiration were positively related to seasonal fluctuations in soil temperature. Seasonal mean soil respiration rates for the experimental warming (EW) and control (CK) plots were 3.98 ± 0.43 and 2.54 ± 0.45 μmol m−2 s−1, respectively, in the winter wheat growing season, and they were 4.59 ± 0.16 and 4.36 ± 0.08 μmol m−2 s−1, respectively, in the soybean growing season. There was a marginally significant level (p = 0.097) for mean nitrification rates between EW and CK plots. Soil temperature and moisture accounted for 58.2% and 58.1% of the seasonal variations observed in the winter wheat and soybean plots, respectively.

Effects of grass coverage and distribution patterns on erosion and overland flow hydraulic characteristics

Grass coverage and its spatial distribution patterns have crucial influences on erosion. The laboratory scouring experiments were conducted to research the influence of grass cover on runoff, erosion rates, and overland flow hydraulic characteristics in the plots with differing grass coverage rates (30, 50, 70, and 90 %), grass distribution patterns (where US, MS, and DS stand for the grass laid on up-slope, middle-slope and down-slope, respectively) and with a bare soil plot (CK) at a slope gradient of 20. The results illustrate that the grassplots had a 2.06–10.94 % runoff reduction and 28.57–75.4 % sediment decreases, respectively, as compared with CK plot. There was no significant difference in the runoff rate among the three grass distribution patterns for the same grass coverage, while DS had the lowest sediment yield rate and greatest sediment yield reduction in comparison with US and MS. The sediment yield rates were found to have a significantly negative exponential relationship with the grass coverage (p < 0.01), while the sediment concentration had a significantly negative linear relationship with the grass coverage (p < 0.01). The overland flow velocity (V) increased with increasing inflow discharges and deceased with increasing grass cover, and it was negatively correlated with the grass coverage following a linear trend (p < 0.01). The mean Froude number (Fr) holds to a similar variation law with the changes in the V. There was no significant relationship found to exist between the grass coverage and Reynolds number (Re). The average Darcy–Weisbach resistance coefficient (f) of the whole slope for grass plots was 2.2–25.6 times of that for CK plot, and f was found to be an exponent correlated with the coverage rate (p < 0.01). In addition, f was negatively correlated with the erosion rate following a power function (p < 0.01); however V, Fr, and Re were positively correlated with the erosion rate (p < 0.01). The sediment yield rate itself was a function of the runoff rate for each treatment, and their relationships could be well described by the linear equation (p < 0.01). These results indicate that both grass coverage rates and distribution patterns have significant effects on hydrological characteristics of overland flow.

Effects of long-term (23 years) mineral fertilizer and compost application on physical properties of fluvo-aquic soil in the North China Plain

The influence of compost and mineral fertilization on soil organic carbon (SOC) and physical properties varied greatly in previous studies because of differences in site conditions such as climate and soil. This study was conducted as a long-term (1989–2012) field experiment to evaluate the effects of mineral fertilization and compost application on SOC content and some physical properties of an intensively cultivated sandy loam soil in the North China Plain. The experiment consisted of seven treatments: organic compost (OM); half organic compost plus half mineral fertilizer NPK (1/2OM1/2NPK); mineral fertilizer NPK (NPK); mineral fertilizer NP (NP); mineral fertilizer PK (PK); mineral fertilizer NK (NK); and unfertilized control (CK), each with four replicates. Relative to CK, the SOC content was higher in all of the compost and mineral fertilizer treatments, but increments in SOC under the compost application treatments were higher than mineral fertilization application. Compost application (OM, 1/2OM1/2NPK) decreased soil bulk density and increased total porosity significantly in comparison with that in the CK plots. Soil bulk density and total porosity for the mineral fertilization treatments, except NP, did not significantly differ from CK. The lowest penetration resistance at 0–20cm soil depth was observed in the NK plots, and the highest penetration resistance was found in the CK plots. Compost application increased the total amount of water-stable macro-aggregates (>0.25mm); however, MWD was not significantly affected by compost application. The MWD in the NK treatment was lower than in CK by 0.2mm, while its variation among NPK, OM, 1/2OM1/2NPK, NP, PK, and CK was not significant. The compost- and mineral fertilizer-treated soil had 34.6–91.7% higher volume of macropores than the CK soil. The OM and 1/2OM1/2NPK-treated soil had a significantly higher proportion of small pores (<3.3μm), and the mineral fertilizer-treated soil did not differ from CK. The hydraulic conductivity in the balanced fertilization plots (OM, 1/2OM1/2NPK, NPK) tended to be higher than in the unbalanced fertilization treatments (NP, PK, and NK) and CK. The results indicated that supplementation with organic manure such as compost is more beneficial to enhance soil fertility and maintain the sustainability of crop production in the North China Plain.

Effectiveness of soil conservation methods in preventing red soil erosion in Southern China

Rainfall, runoff (surface runoff and interflow) and soil loss were recorded from 2002 to 2005 in an experiment with four treatments on sloping red soil land in southern China. Treatments consisted of bare sloping ground (control check, CK), interplanting with soybean in spring or radish in autumn (I), level terrace (i.e., grass planted on the riser and bunds built at the edge of a bench terrace) (II), and level terraces of orchards with Bahia grass planted on the riser (III). The surface runoff and erosion in treatment II and III during the four years were low despite the occurrence of potentially erosive rains. By contrast, the CK plot had both the highest surface runoff coefficient and the highest sediment yield among all the plots. The surface runoff and soil erosion of the CK plot significantly differed from that of the treatment plots (p I > III > II, whereas their order in terms of interflow was II > III > I > CK. The effects of treatment II were excellent, indicating that level terrace (i.e., grass planted on the riser and bunds built at the edge of a bench terrace) can be an excellent practice for soil and water conservation on sloping red soil land. Soil loss in southern China can be reduced through the widespread use of this approach.

Simulated acid rain changed the proportion of heterotrophic respiration in soil respiration in a subtropical secondary forest

Acid rain is a matter of concern in southern China. We explored how soil respiration (Rs) and heterotrophic respiration (Rh) rates changed when subjected to simulated acid rain (SAR) environment for 3 years (from March 2010 to February 2013) in a secondary forest in subtropical China. The field experiment was arranged in a split-plot design, with 4 main blocks. Each block was split into un-trenched (Rs) and trenched (Rh) treatments. Four SAR treatments of CK (control, deionized water), A1 (pH 4.0), A2 (pH 3.0), and A3 (pH 2.0) were randomly assigned in each of the Rs and Rh treatments. Soil CO2 fluxes as well as soil temperature and moisture at a depth of 5cm were measured weekly. Different SAR treatments exhibited similar seasonal patterns of Rs and Rh. Mean annual Rs rates in CK, A1, A2, and A3 plots were 878.2±100.8, 919.4±33.1, 865.6±62.5, and 925.2±20.5gCm−2yr−1, respectively, over 3 years; SAR had no significant effects on Rs. Rh, however, was significantly (P<0.05) affected by the lowest SAR pH level (A3). On overage of 3 years, annual Rh rates in CK, A1, A2 and A3 plots were 606.7±52.4, 663.5±35.5, 728.2±60.7, and 760.1±42.2gCm−2yr−1, respectively. Statistical analysis showed that SAR significantly (P<0.05) increased the proportion of Rh in Rs. The relationship between residual Rs (or Rh) based on soil temperature and observed Rs (or Rh) and soil moisture could be well fitted in a quadratic model.

Asymmetric warming effects on N dynamics and productivity in rice (Oryza sativa L.)

Climate warming exhibits strong diurnal variations, with higher warming rates being observed at nighttime, which significantly affects rice (Oryza sativa L.) growth and grain yield. The objective of this study was to determine the effects of asymmetric warming (all-day warming, AW; daytime warming from 07:00 to 19:00, DW; nighttime warming from 19:00 to 07:00, NW, and a control, CK) on rice nitrogen (N) dynamics and productivity. Two rice bucket warming experiments were performed in Nanjing in Jiangsu Province, China, using the free air temperature increase (FATI) technique. The daily mean temperatures in the rice canopy in the AW, DW and NW plots were 2.0, 1.1 and 1.3ºC higher than those in the rice canopy in the CK plots, respectively. The results indicated that the total N accumulation of rice was 8.27–40.53% higher in the warming treatment than in the control during the jointing, anthesis and maturity stages. However, there was no significant difference detected among the three warming treatments. The warming treatment substantially decreased N translocation efficiency, leading to the retention of more N in the plant stems during grain filling. The warming treatment also decreased the N harvest index, N utilization efficiency based on grain yield and N utilization efficiencies based on biomass in both growing seasons. The warming treatment significantly increased the aboveground biomass (9.26–16.18%) in the jointing stage but decreased it (2.75–9.63%) in the maturity stage. Although DW increased the carbon (C) gain by photosynthesis and NW increased the C loss by night respiration, the daytime higher-temperature treatment affected rice photosynthesis and reduced its photosynthetic rate and product. This effect may be one of the primary reasons for the insignificant difference in the aboveground biomass between the DW and NW treatments. In the AW, DW and NW plots, the grain yield was reduced by an average of 10.07, 5.05 and 7.89%, respectively, across both years. The effective panicles and grains per spike tended to decrease in the warmed plots, whereas irregular changes in the 1000-grain weight were observed. Our results suggest that under the anticipated climate warming, rice productivity would further decline in the Yangtze River Basin.

The impact of excretal returns from yak and Tibetan sheep dung on nitrous oxide emissions in an alpine steppe on the Qinghai-Tibetan Plateau

This study describes the impact of excretal returns derived from livestock dung on nitrous oxide (N2O) emissions in a grazed alpine grassland ecosystem. N2O flux, vegetation and soil characteristics were measured in an alpine steppe on the Qinghai-Tibetan Plateau. Measurements were obtained from control (CK) plot and experimental plot to which either yak dung (YD) or Tibetan sheep dung (SD) was added. We found significantly lower surface soil temperature and higher soil moisture in the YD plot than in either the CK or SD plot. The application of YD resulted in significantly less biomass of aboveground vegetation, lower carbon and nitrogen uptake, and significantly higher cumulative N2O emission in comparison to the CK or SD treatment. N2O from SD treatment was probably mainly produced via nitrification, while N2O from YD treatment was primarily produced by denitrification. Emission factors of N2O for both YD and SD were far lower than the default values proposed by the IPCC and the release of N2O from YD and SD patches is low.

Night-time warming affects N and P dynamics and productivity of winter wheat plants

Zhang, Y., Li, R. and Wang, Y. 2013. Night-time warming affects N and P dynamics and productivity of winter wheat plants. Can. J. Plant Sci. 93: 397–406. The daily night-time temperature has currently increased faster than the daily daytime temperature over much of the Earth's surface. To understand how night-time warming affects the dynamics of winter wheat performance, open-field experiments, in which temperatures were elevated by covering the plots at night with reflective curtains, were conducted in the 2010/2011 and 2011/2012 growing seasons. The results show that, on average, night-time temperatures increased by 0.9°C under night-time covered (NC) treatment compared with the uncovered (CK). Plant total N accumulation was 17–43% higher in NC treatment than CK during the jointing, anthesis and ripening stages, whereas plant total P was affected by NC treatment depending on growing stage. Night-time covered treatment substantially decreased N translocation efficiency, leading to more N retained in plant stems during grain filling. Although P translocated to grain was 29–41% higher in NC plots than CK plots, NC treatment decreased post-anthesis P uptake by 27–41%, depending on the growing season, resulting in evident reduction of P harvest index and P utilization efficiency. When night-time temperature increased, grain yield was reduced by 6–25% due to a combination of decreased productive spikes, a lower number of kernels per spike and reduced weight of grain per kernel.

Effects of contrasting soil management regimes on total and labile soil organic carbon fractions in a loess soil in China

Labile soil organic carbon pools are valuable indicators of soil quality, early changes in soil total organic carbon (TOC) stocks, and (hence) changes in soil carbon sequestration pools and dynamics induced by changes in soil management practices. To improve the management of loess soils in China, we have examined effects of soil and nutrient management treatments applied in a 20-year experiment on TOC and the following fractions: particulate organic carbon (POC), light fraction organic carbon (LFOC), microbial biomass carbon (MBC) and permanganate oxidizable carbon (KMnO4 C). The soil management regimes were cropland abandonment (Abandonment), bare fallow without vegetation (Fallow) and a wheat-maize cropping system (Cropping). Cropping was combined with the following nutrient management treatments: control (CK, no nutrient input), nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK, straw plus NPK (SNPK) and two levels of manure (M, 13.7 and 20.6tha−1) plus NPK (M1NPK and M2NPK). After 20years, the Fallow treatment resulted in significantly lower TOC by 22% and labile C fractions by 29%–43% except MBC than Cropping, while Abandonment markedly increased all labile C fractions by 43%–64% except POC relative to Cropping, but the Abandonment and Cropping regimes resulted in similar TOC contents (10.75gkg−1 and 10.16gkg−1, respectively). Of the four C fractions, LFOC and KMnO4 C were the most sensitive indicators of changes in TOC induced by the soil management regimes. Under Cropping, TOC contents were similar in NP, NPK and SNPK plots, and significantly higher than those in CK plots (by 34%, 32% and 45%, respectively). Manure addition further enhanced TOC contents, which were highest following the M2NPK treatment (13.88gkg−1). Labile C fractions were also significantly higher following the treatments including organic amendment than following applications solely of chemical fertilizers, except that the SNPK, NP and NPK treatments resulted in similar LFOC contents. Application solely of chemical fertilizers had no significant effects on LFOC and KMnO4 C fractions compared with CK. Nevertheless, application of NP or NPK significantly increased contents of POC and MBC relative to CK (by 115% and 90% or 31% and 53%, respectively). Thus, LFOC and KMnO4 C fractions were not sensitive indicators of changes in TOC induced by mineral nutrient management practices under current conditions. Overall, given the minor differences between the effects of the NP and NPK treatments, application of manure and NP appears to be the most suitable management practice for improving TOC sequestration in the loess soil.

Nitrous oxide emissions from a maize field during two consecutive growing seasons in the North China Plain

Abstract Nitrous oxide (N 2O) emissions from a maize field in the North China Plain (Wangdu County, Hebei Province, China) were investigated using static chambers during two consecutive maize growing seasons in the 2008 and 2009. The N 2O pulse emissions occurred with duration of about 10 days after basal and additional fertilizer applications in the both years. The average N 2O fluxes from the CK (control plot, without crop, fertilization and irrigation), NP (chemical N fertilizer), SN (wheat straw returning plus chemical N fertilizer), OM-1/2N (chicken manure plus half chemical N fertilizer) and OMN (chicken manure plus chemical N fertilizer) plots in 2008 were 8.51, 72.1, 76.6, 101, 107 ng N/(m 2·sec), respectively, and in 2009 were 33.7, 30.0 and 35.0 ng N/(m 2·sec) from CK, NP and SN plots, respectively. The emission factors of the applied fertilizer as N2O-N (EFs) were 3.8% (2008) and 1.1% (2009) for the NP plot, 3.2% (2008) and 1.2% (2009) for the SN plot, and 2.8% and 2.2% in 2008 for the OM-1/2N and OMN plots, respectively. Hydromorphic properties of the investigated soil (with gley) are in favor of denitrification. The large differences of the soil temperature and water-filled pore space (WFPS) between the two maize seasons were suspected to be responsible for the significant yearly variations. Compared with the treatments of NP and SN, chicken manure coupled with compound fertilizer application significantly reduced fertilizer loss rate as N 2O-N.

Influence of fertilisation regimes on a nosZ‐containing denitrifying community in a rice paddy soil

Denitrification is a microbial process that has received considerable attention during the past decade since it can result in losses of added nitrogen fertilisers from agricultural soils. Paddy soil has been known to have strong denitrifying activity, but the denitrifying microorganisms responsible for fertilisers in paddy soil are not well known. The objective of this study was to explore the impacts of 17-year application of inorganic and organic fertiliser (rice straw) on the abundance and composition of a nosZ-denitrifier community in paddy soil. Soil samples were collected from CK plots (no fertiliser), N (nitrogen fertiliser), NPK (nitrogen, phosphorus and potassium fertilisers) and NPK + OM (NPK plus organic matter). The nitrous oxide reductase gene (nosZ) community composition was analysed using terminal restriction fragment length polymorphism, and the abundance was determined by quantitative PCR. Both the largest abundance of nosZ-denitrifier and the highest potential denitrifying activity (PDA) occurred in the NPK + OM treatment with about four times higher than that in the CK and two times higher than that in the N and NPK treatments (no significant difference). Denitrifying community composition differed significantly among fertilisation treatments except for the comparison between CK and N treatments. Of the measured abiotic factors, total organic carbon was significantly correlated with the observed differences in community composition and abundance (P < 0.01 by Monte Carlo permutation). This study shows that the addition of different fertilisers affects the size and composition of the nosZ-denitrifier community in paddy soil.

Long‐Term Field Fertilization Significantly Alters Community Structure of Ammonia‐Oxidizing Bacteria rather than Archaea in a Paddy Soil

Long‐term field fertilization experiments may provide useful insight into the relative contributions of NH3–oxidizing bacteria (AOB) and NH3–oxidizing archaea (AOA) to soil nitrification. In this study, the abundance and composition of AOB and AOA were investigated in bulk soil from paddy field plots (4 by 5 m) that received no fertilization (CK), 180 kg urea N ha−1 yr−1 (NPK), or 180 kg urea N plus 4500 kg rice (Oryza sativa L.) straw ha−1 yr−1 (NPK/OM) since 1988 (each with three replicated plots). Our results clearly indicate that long‐term fertilization (22 yr) significantly altered the community structure of AOB rather than AOA in the soil within fertilized plots compared with the CK plot. Quantitative polymerase chain reaction analysis of the amoA genes that encode the ammonia monooxygenase subunit A revealed that the AOB in the fertilized plots were 50 times more abundant than in the CK plot. Denaturing gradient gel electrophoresis fingerprinting of the amoA genes demonstrated a drastic shift in the AOB community structure, resulting in highly enriched AOB similar to Nitrosospira cluster 3 in the fertilized plots. In contrast, the population size and composition of the AOA community remained largely unchanged in all plots. Furthermore, a positive correlation was observed between the bacterial rather than archaeal amoA gene copy numbers and potential nitrification activity among the soils. The distinct responses of AOA and AOB to long‐term field fertilization were probably related to the availability of NH3. Our results suggest that AOB might play major roles in the NH3 oxidation that occurs in bulk soil under the in situ fertilized paddy field conditions tested in this study.

Long‐term‐fertilization effects on soil organic carbon, physical properties, and wheat yield of a loess soil

AbstractThe large dryland area of the Loess Plateau (China) is subject of developing strategies for a sustainable crop production, e.g., by modifications of nutrient management affecting soil quality and crop productivity. A 19 y long‐term experiment was employed to evaluate the effects of fertilization regimes on soil organic C (SOC) dynamics, soil physical properties, and wheat yield. The SOC content in the top 20 cm soil layer remained unchanged over time under the unfertilized plot (CK), whereas it significantly increased under both inorganic N, P, and K fertilizers (NPK) and combined manure (M) with NPK (MNPK) treatments. After 18 y, the SOC in the MNPK and NPK treatments remained significantly higher than in the control in the top 20 cm and top 10 cm soil layers, respectively. The MNPK‐treated soil retained significant more water than CK at tension ranges from 0 to 0.25 kPa and from 8 to 33 kPa for the 0–5 cm layer. The MNPK‐treated soil also retained markedly more water than the NPK‐treated and CK soils at tensions from 0 to 0.75 kPa and more water than CK from 100 to 300 kPa for the 10–15 cm layer. There were no significant differences of saturated hydraulic conductivity between three treatments both at 0–5 and 10–15 cm depths. In contrast, the unsaturated hydraulic conductivity in the MNPK plot was lower than in the CK plot at depths of 0–5 cm and 10–15 cm. On average, wheat yields were similar under MNPK and NPK treatments and significantly higher than under the CK treatment. Thus, considering soil‐quality conservation and sustainable crop productivity, reasonably combined application of NPK and organic manure is a better nutrient‐management option in this rainfed wheat–fallow cropping system.

Effects of elevated UV-B radiation on ecosystem and soil respiration in a winter wheat farmland

O 3 concentration in the stratosphere is decreasing, resulting in higher solar ultraviolet-B radiation (UV-B, 280–320 nm) to the Earth’s surface. Enhanced levels of UV-B radiation may, in turn, alter ecosystem processes such as respiration. In this study, daily changes of ecosystem and soil respiration rates under modulated 20% supplementation of UV-B and ambient UV-B conditions (CK) were investigated in the 2007–08 winter wheat ( Triticum aestivum L.) season in a farmland nearing Nanjing city, south-east China, in order to determine the effects of elevated UV-B radiation on these processes. A paired t-test indicated that the effects of elevated UV-B radiation on ecosystem respiration varied across different measuring periods. Significantly lower ecosystem respiration rates in the elevated UV-B plots were found at the later growth (anthesis and beginning grain filling) stages. Elevated UV-B radiation significantly reduced soil respiration rates during each development stages. As far as the whole measuring period is concerned, elevated UV-B radiation significantly ( p < 0.05) reduced both ecosystem respiration and soil respiration. The seasonal mean ecosystem respiration rates for the CK and UV-B treatments were 1144.1 and 1008.3 mg CO 2 m −2 h −1, respectively, and the seasonal mean soil respiration rates for the two treatments were 286.0 and 249.3 mg CO 2 m −2 h −1, respectively. Regression analysis showed that elevated UV-B radiation significantly reduced temperature sensitivity of ecosystem respiration, with the Q 10 decreasing from 1.73 in the CK plots to 1.63 in the elevated UV-B plots. The Q 10 of soil respiration was not significantly affected by enhanced UV-B radiation. The exponential response curve (ecosystem respiration VS temperature) might be constructed with less-damaged plants at the lower temperature and more-damaged plants at the higher temperature, which yielded a lower temperature sensitivity of ecosystem respiration in the UV-B treatment.