A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design w...A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.展开更多
A field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to ...A field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to 2002. The local cropping sequence of wheat, wheat-beans, maize, and wheat over the 4-year period was adopted. A micro-plot study using ^15N-lahelled fertilizer was carried out to determine the fate of applied N fertilizer in the first year. When N fertilizer was applied wheat （years 1, 2 and 4） and maize （year 3） grain yield increased significantly （P 〈 0.05） （〉 30%）, with no significant yield differences in normal rainfall years （Years 1, 2 and 3） for N application at the commonly application rate and at 2/3 of this rate. Grain yield of wheat varied greatly between years, mainly due to variation in annual rainfall. Results of ^15N studies on wheat showed that plants recovered 36.6%-38.4% of the N applied, the N remained in soll （0-40 cm） ranged from 29.2% to 33.6%, and unaccounted-for N was 29.5%-34.2%. The following crop （wheat） recovered 2.1%- 2.8% of the residual N from N applied to the previous wheat crop with recovery generally decreasing in the subsequent three crops （beans, maize and wheat）.展开更多
Fate of urea nitrogen (N) applied to rape grown on a red soil was investigated by the ￣(15)N mass balancetechnique, and efficiency of urea and effect of nutrients balance in raising rape yield were investigated ina f...Fate of urea nitrogen (N) applied to rape grown on a red soil was investigated by the ￣(15)N mass balancetechnique, and efficiency of urea and effect of nutrients balance in raising rape yield were investigated ina field plot experiment. One hundred and thirty-eight kg N/ha, 86 kg N/ha as basal dressing and 52 kgN/ha as top dressing, was applied with band application technique. The experiment was conducted in thesoutheast of China, near Yingtan City, Jianxi Province.Results from is￣(15)N mass balance study showed that when urea was applied as basal dressing the plantrecovery was 44.0% of the applied N for Theatment T (with application of N, P, K, B and lime). Plantrecoveries were 38.0%-40.5% for Treatments -K, -B, -lime and +RS (without application of K, B or limeas well as with additional rice straw compared with Theatment T), which were not significantly differentfrom Treatment T. In contrast, plant recovery was only 5.1% for Treatment-P (without application of P),indicating that P was the factor limiting N uptake by rape. However, N remaining in 0-0.30 m soil was highup to 71.6% for Theatment -P, while the corresponding data were 33.0%-42.6% for the other treatments.The total recovery of applied N (including plant recovery and N remaining in 0-0.60 m soil) was 91.5% forTreatment T when urea was applied as basal dressing, while almost all the applied N was recovered when ureawas applied as top dressing. It was suggested that N loss was greatly controlled by using band applicationmethod in this experiment.Results from the field plot experiment showed that N supply capacity of this red soil was very low, andthe efficiency of the applied N was quite high, 7.1 kg rape seed was increased by application of one kg N forTreatmentT. Nitrogen and phosphorus were the key factors limiting rape yield, and the yield was very lowwhen neither of them was applied. The yield in TreatmentK was significantly lower than that in TYeatmentT, with the former accounting for 77% of the later.展开更多
Nitrification-denitrification losses of ￣15N-labelled nitrate and ammonium applied to the rhizosphere andnonrhizosphere of flooded rice were evaluated in 2 greenhouse rhizobox experiments. The loss of added Nvia deni...Nitrification-denitrification losses of ￣15N-labelled nitrate and ammonium applied to the rhizosphere andnonrhizosphere of flooded rice were evaluated in 2 greenhouse rhizobox experiments. The loss of added Nvia denitrification was estimated directly by measuring the total fluxes of (N_2O+N_2)￣15N. It was found that 67% and51%-56% of ￣15N-nitrate added to rice rhizosphere were lost as (N_2O+N_)-￣15N in the 2 experiments, respectively,which were comparable to that added to nonrhizosphere soil (70%and47%, respectively), implying that tbedenitrifying activity in rice rhizosphere was as high as that in nonrhizosphere soil. However, only trace amounts(0-0.3% of added N) were recovered as (N_2O+N_2)-￣15N when ￣15N-ammonium was applied to either rhizosphere ornonrhizosphere, which seems to indicate that the nitrifying activity in the either rhizosphere or nonrhizosphere soilswas quite low. The apparent denitrification calculated from ￣15N balance studies was 10%-47% higher than the totalflux of (N_2O+N_2)-￣15N. Reasons for the large differences can not be explained satisfactorily. Though the denitrifyingactivity in rhizospbere was high and comparable to that in nonrhizosphere soil, presumably due to the low nitrifyingactivity and/ or the strong competition of N uptake against denitrification, the nitrification-denitrification takingplace in rhizosphere could not be an important mechanism of loss of ammonium N in flooded rice-soil system.展开更多
基金Project supported by the National Natural Science Foundation of China (No. 40171048)the Science and Technique Key Project of the Tenth Five-Year Plan of China (No. 2002BA516A03)
文摘A field experiment was conducted on Chinese cabbage （Brassica campestris L. ssp. pekinensis （Lour.） Olsson） in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates： zero chemical fertilizer N （CK）; urea at rates of 300 kg N ha^-1 （U300） and 600 kg N ha^-1 （U600）, both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N ha^-1 （PCU180） as a basal application. The acetylene inhibition technique was used to measure denitrification （N2 ＋ N2O） from intact soil cores and N2O emissions in the absence of acetylene. Results showed that compared to （3K total denitrification losses were significantly greater （P ≤ 0.05） in the PCU180, U300, and U600 treatments,while N2O emissions in the U300 and U600 treatments were significantly higher （P ≤ 0.05） than （3K. In the U300 and U600 treatments peaks of denitrification and N2O emission were usually observed after N application. In the polymer-coated urea treatment （PCU180） during the period 20 to 40 days after transplanting, higher denitrification rates and N2O fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and N2O emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N2O emissions tended to decrease. A significant （P ≤0.01） positive correlation occurred between denitrification （r = 0.872） or N2O emission （r = 0.781） flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.
基金Project supported by the International Atom Energy Agency (IAEA) (NO. 302-D1-CRP-9986) and the National Basic Research Program of China (NO. 2005CB121102).
文摘A field experiment with four treatments and four replicates in a randomized complete block design was conducted at the Changwu Experimental Station in Changwu County, Shaanxi Province, of Northwest China from 1998 to 2002. The local cropping sequence of wheat, wheat-beans, maize, and wheat over the 4-year period was adopted. A micro-plot study using ^15N-lahelled fertilizer was carried out to determine the fate of applied N fertilizer in the first year. When N fertilizer was applied wheat （years 1, 2 and 4） and maize （year 3） grain yield increased significantly （P 〈 0.05） （〉 30%）, with no significant yield differences in normal rainfall years （Years 1, 2 and 3） for N application at the commonly application rate and at 2/3 of this rate. Grain yield of wheat varied greatly between years, mainly due to variation in annual rainfall. Results of ^15N studies on wheat showed that plants recovered 36.6%-38.4% of the N applied, the N remained in soll （0-40 cm） ranged from 29.2% to 33.6%, and unaccounted-for N was 29.5%-34.2%. The following crop （wheat） recovered 2.1%- 2.8% of the residual N from N applied to the previous wheat crop with recovery generally decreasing in the subsequent three crops （beans, maize and wheat）.
文摘Fate of urea nitrogen (N) applied to rape grown on a red soil was investigated by the ￣(15)N mass balancetechnique, and efficiency of urea and effect of nutrients balance in raising rape yield were investigated ina field plot experiment. One hundred and thirty-eight kg N/ha, 86 kg N/ha as basal dressing and 52 kgN/ha as top dressing, was applied with band application technique. The experiment was conducted in thesoutheast of China, near Yingtan City, Jianxi Province.Results from is￣(15)N mass balance study showed that when urea was applied as basal dressing the plantrecovery was 44.0% of the applied N for Theatment T (with application of N, P, K, B and lime). Plantrecoveries were 38.0%-40.5% for Treatments -K, -B, -lime and +RS (without application of K, B or limeas well as with additional rice straw compared with Theatment T), which were not significantly differentfrom Treatment T. In contrast, plant recovery was only 5.1% for Treatment-P (without application of P),indicating that P was the factor limiting N uptake by rape. However, N remaining in 0-0.30 m soil was highup to 71.6% for Theatment -P, while the corresponding data were 33.0%-42.6% for the other treatments.The total recovery of applied N (including plant recovery and N remaining in 0-0.60 m soil) was 91.5% forTreatment T when urea was applied as basal dressing, while almost all the applied N was recovered when ureawas applied as top dressing. It was suggested that N loss was greatly controlled by using band applicationmethod in this experiment.Results from the field plot experiment showed that N supply capacity of this red soil was very low, andthe efficiency of the applied N was quite high, 7.1 kg rape seed was increased by application of one kg N forTreatmentT. Nitrogen and phosphorus were the key factors limiting rape yield, and the yield was very lowwhen neither of them was applied. The yield in TreatmentK was significantly lower than that in TYeatmentT, with the former accounting for 77% of the later.
文摘Nitrification-denitrification losses of ￣15N-labelled nitrate and ammonium applied to the rhizosphere andnonrhizosphere of flooded rice were evaluated in 2 greenhouse rhizobox experiments. The loss of added Nvia denitrification was estimated directly by measuring the total fluxes of (N_2O+N_2)￣15N. It was found that 67% and51%-56% of ￣15N-nitrate added to rice rhizosphere were lost as (N_2O+N_)-￣15N in the 2 experiments, respectively,which were comparable to that added to nonrhizosphere soil (70%and47%, respectively), implying that tbedenitrifying activity in rice rhizosphere was as high as that in nonrhizosphere soil. However, only trace amounts(0-0.3% of added N) were recovered as (N_2O+N_2)-￣15N when ￣15N-ammonium was applied to either rhizosphere ornonrhizosphere, which seems to indicate that the nitrifying activity in the either rhizosphere or nonrhizosphere soilswas quite low. The apparent denitrification calculated from ￣15N balance studies was 10%-47% higher than the totalflux of (N_2O+N_2)-￣15N. Reasons for the large differences can not be explained satisfactorily. Though the denitrifyingactivity in rhizospbere was high and comparable to that in nonrhizosphere soil, presumably due to the low nitrifyingactivity and/ or the strong competition of N uptake against denitrification, the nitrification-denitrification takingplace in rhizosphere could not be an important mechanism of loss of ammonium N in flooded rice-soil system.
