[Impact of Exogenous Nitrogen Import on Sediment Denitrification and N2O Emissions in Ditches Under Different Land Uses].

Farmland drainage ditch soil can consume part of the agricultural non-point nitrogen through nitrification-denitrification processes. Paddy fields, vegetable land, and orchards are the main types of land uses in the Taihu Lake region, and many drainage ditches are distributed across these lands. The way exogenous nitrogen is imported to drain ditches under different land uses differs significantly, which can directly affect the nitrogen consumption ability of the channels. A soil incubation experiment was conducted under laboratory conditions to study the denitrification loss and N2O emissions of drainage ditch soil under different land uses. In this study, drainage ditch sediment was collected from orchards, paddy fields, and vegetable land in the Taihu Lake region. Five different NO3--N content import levels were set:0, 0.5, 1.0, 5.0, and 10 mg·L-1, which were denoted as N0, N1, N2, N3, and N4, respectively. The results showed that exogenous nitrogen input stimulated sediment denitrification in the drainage ditches. The sediment denitrification rates of the three types of channels increased significantly with the increase of input NO3--N concentration (P<0.05). There was a significant linear positive correlation between the cumulative denitrification loss and input NO3--N concentration (R2>0.75). Excluding for the vegetable land sediment, the N2O emission rate and cumulative emissions did not increase significantly with the increase of input NO3--N concentration (P>0.05). There was no significant difference in the denitrification and N2O emissions among the three kinds of channel sediment, with no or low exogenous nitrogen input (N0and N1) (P>0.05). As the input NO3--N concentration increased, especially under the condition of high exogenous nitrogen input (N3and N4), the nitrogen consumed via denitrification in orchard and paddy field sediment was significantly higher than that in vegetable land sediment (P<0.05), whereas the N2O emissions of drainage ditch sediment from the vegetable land was significantly higher than that of the other two channel sediments (P<0.05). The mineralization rate of ditch soil organic carbon had a positive correlation with denitrification rate (n=15), and microbial mineralization (CO2-C) promoted the nitrification and denitrification of the drainage ditch soils.

Mechanisms of enhanced inorganic phosphorus accumulation by periphyton in paddy fields as affected by calcium and ferrous ions.

The effect of periphyton propagation in paddy fields on phosphorus biogeochemical cycling has received little attention. In this phytotron study, inorganic phosphorus (Pi) accumulation by periphyton was investigated for varying inputs of calcium [Ca(II)] or ferrous­iron [Fe(II)], and lighting conditions. Results indicated that additions of Ca(II) or Fe(II) enhanced abiotic accumulation of Pi by up to 16 times, and decreased solution Pi concentration by up to 50%, especially under light condition. The enhanced Pi accumulation into periphyton intensified with increasing Pi concentration, and Pi accumulation showed a positive linear relationship with Ca or Fe accumulation. Abiotic accumulation of Pi induced by Ca(II) was mainly through Ca-phosphate precipitation, and co-precipitation of P with carbonates at pH>8. Accumulation with added Fe(II) was mainly considered to be through Fe(III) phosphate precipitation coupled with adsorption of Pi by ferric hydroxides. Moreover, Fe(II) was more effective than Ca(II) in promoting abiotic accumulation of Pi by periphyton. Our results indicate the potential for controlling environmental factors to enhance the role of periphyton in biogeochemical cycling and P-use efficiency in paddy rice fields and to reduce P discharged to neighboring water bodies.

[Effects of Biochar Amendment and Irrigation on Denitrification Losses in Greenhouse Tomato Fields].

Biochar addition and irrigation are normal farm practices for tomatoes management, while their impacts on denitrification are less known. In this study, three irrigation treatments(hereafter main plots)were set as 50% (W50%), 75% (W75%) and 100% (W100%) of reference evapotranspiration (ET0), and the subplots coupled three biochar treatments at the rates of 0 (B0), 25 t·hm-2 (B25) and 50 t·hm-2 (B50). Typical soil samples in each plot were collected when tomatoes were harvested in 2014 and 2015. We used acetylene inhibition method to study the denitrification loss, and also measured N2O emissions of tomato soil without acetylene amendment. The results showed that biochar and irrigation significantly changed the physical and chemical properties of the soil. Adding biochar improved total carbon, total nitrogen content and pH of the soil, while reduced the content of NH4+-N and NO3--N compared to B0. On the contrary, irrigation reduced the amount of total nitrogen and total carbon content. As a result, both biochar and irrigation significantly reduced denitrification losses (P<0.05). Moreover, the interaction of biochar and irrigation significantly reduced soil inorganic nitrogen and denitrification losses (P<0.05),and the orders of the influencing factors of NO3--N were irrigation, biochar, their interactions in turn, the orders of the influencing factors of NH4+-N were biochar, irrigation, their interactions in turn, the orders of the influencing factors of denitrification losses were irrigation, biochar, their interactions in turn. Denitrification losses were positively related to inorganic nitrogen content in the soil, CO2mineralization rates and N2O emission rates. The ratio of N2O/DN, ranging from 0.31% to 1.88%, was significantly affected by biochar and irrigation treatment in the fields (P<0.05).

[Denitrification Loss and N2O Emission from Different Carbon Inputs in Orchard Drains Sediments].

The orchard is an important economic crop in Taihu Lake region. Heavy nitrogen application in orchard results in great nitrogen loss to drainage ditch, and unbalanced carbon nitrogen ratio. Therefore, carbon might be an important limiting factor for sediment nitrification and denitrification. A soil incubation experiment controlled by the acetylene inhibition method was conducted under laboratory conditions to study the denitrification loss and N2O emissions of orchard drainage ditch soil. We designed five carbon input levels of 0, 5, 25, 50 and 100 mg·L-1, which were noted as C0, C1, C2, C3 and C4, respectively, meanwhile there was 5 mg·L-1 net nitrogen input in the form of KNO3 in each treatment. The results showed that carbon inputs could stimulate both denitrification rates (DN) and N2O emission rates. Carbon and nitrogen ratio had a significant effect on N2O emission rates and denitrification loss rates (P<0.05). When the carbon and nitrogen ratio was 10:1, total cumulative denitrification losses and N2O emissions were both highest (319.26 µg·kg-1 and 6.20 µg·kg-1, respectively) among the treatments, which accounted for 1.28% and 0.02% of net nitrogen input, respectively. This result indicated that the carbon and nitrogen ratio of 10:1 was most favorable for N2O emissions and denitrification process in sediments.

[Temporal and spatial variations of total nitrogen and total phosphorus in the typical reaches of Qinhuai River].

The year-round concentrations of total nitrogen (TN) and total phosphorus (TP) were monitored from June 2010 to May 2011 in the typical reaches of the Qinhuai River. The spatial and temporal variations in TN and TP concentrations and the pollution status of the river water were investigated using typical statistics analysis. Results showed that the river water was seriously polluted in terms of TN and TP, and that the concentrations of both TN and TP showed high spatial and temporal variations. The average TN concentrations of the river water in the traditionally managed agricultural area, intensively managed agricultural area, and urban area were 1.80, 3.97 and 9.25 mg L(-1), respectively; The corresponding average TP concentrations were 0.03, 0.11 and 0.50 mg L(-1), respectively, showing similar spatial patterns with those of TN. The spatial variations in TN and TP concentrations in river water indicated that the urban area and intensively managed agricultural area, rather than the traditionally managed agricultural area, were the major sources for TN and TP in the river water. The average TN concentrations of river water during the wet season and dry season were 1.89 and 4.58 mg x L(-1), respectively; and the corresponding average TP concentrations were 0.11 and 0.14 mg x L(-1), respectively. The temporal variations indicated that the pollution status of the river water was more serious during the dry season than that during the wet season. Assessment results of eutrophication indicated that the majority of Qinhuai River reaches were in the stage of eutrophication, thus deserving immediate controlling measures.

[Effects of applying nitrogen fertilizer and fertilizer additive on rice yield and rice plant nitrogen uptake, translocation, and utilization].

A field experiment was conducted in the Taihu Lake region of southern Jiangsu to study the effects of applying nitrogen (N) fertilizer and fertilizer additive on the rice yield and the rice plant N uptake, translocation, and utilization. Applying N fertilizer had significant positive effects on the rice yield, accumulative absorbed N at all growth stages and at each growth stage, and N translocation rate after anthesis (P < 0.01). However, when the N application rate exceeded 200 kg x hm(-2), its yield-increasing effect was not significant (P > 0.05). The N translocation rate after anthesis and the N fertilizer use efficiency decreased with increasing N application rate. Applying fertilizer additive further improved the rice yield, accumulative absorbed N, N translocation rate after anthesis, and N fertilizer use efficiency, and this effect was more evident when the N application rate was equal to or greater than 200 kg x hm(-2). Relatively high rice yield and N use efficiency were achieved when applying 150 kg x hm(-2) of N fertilizer without the application of fertilizer additive.