Effect of Indigenous Nitrogen Supply of Soil on the Grain Yield and Fertilizer-N Use Efficiency in Rice

The effects of application of N fertilizer on wheat on the grain yield and N use efficiency （FNUE） of rice in the wheat-rice rotation system, as well as on the soil fertility were studies. N-fertilizer application on wheat significantly increased total N, arnrnoniurn-N and nitrate-N contents in paddy field, resulting in high indigenous N supply of soil （INS）. Compared with low INS, the effect of N rate on the grain yield of rice was reduced significantly, and FNUE was decreased under high INS. These results indicated that high INS was one of the main reasons for the low FNUE in rice.

Effects of Mg on C and N Metabolism of Soybean at Different Nitrogen Supplying Levels

A pot experiment was conducted to study the effects of magnesium on carbon and nitrogen metabolism of soybean at different nitrogen supplying levels. The results showed that the effects of magnesium at low nitrogen rate on N content, soluble protein, soluble sugar contents were not alike at different growth stage, although nodule dry weights raised, the yield and protein content of seeds decreased, however, the oil content was improved. The application of magnesium at medium and high nitrogen supplying levels promoted the uptake of N effectively, increased the soluble protein and soluble sugar contents, but the nodule dry weights of application magnesium at medium nitrogen supplying level decreased and the yield increased only a little despite the improved quality. Application of magnesium at high nitrogen supplying level raised nodule dry weights and soybean yield significantly, the quality of seeds was also improved.

Estimation of the Biological Methods of Assessing Soil N-Supplying Capacity in Calcareous Soil

Although many biological methods are used to determine soil nitrogen supplying capacity, there are certain differences in the results for different types of soils and various ways of measurement due to the complexity of soil N conformation, the high variance of soil and microorganism, and the difference of environment. Therefore, it is not clear about which biologic incubation method is better for calcareous soil. In this study, pot experiments were performed by using 25 different calcareous surface soil samples on the Loess Plateau and taking the N uptake of wheat and corn with leaching soil initial nitrate and without leaching in pot experiments as the control to investigate the difference of eight biological incubation methods for reflecting soil nitrogen supply capacity. The eight biological methods are waterlogged incubation, aerobic incubation for 2 weeks and for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks, long-term alternate leaching aerobic incubation （and N mineralization potential, No）, short-term leaching aerobic incubation, microbial biomass carbon （Bc）, and microbial biomass nitrogen （BN） method, respectively. Among these methods, the dry-wet alternation aerobic incubation and aerobic incubation for 4 weeks were the modification of the method of aerobic incubation for 2 weeks according to the actual farmland moisture. The results showed that the correlation coefficients between these methods and crop uptake N with leaching soil initial nitrate were 0.530, 0.700, 0.777, 0.768, 0.764 （and 0.790, No）, 0.650, 0.555, and 0.465, respectively （r0.05 = 0.369, r0.0l = 0.505）. While without leaching soil initial nitrate, their coefficients were 0.351, 0.963, 0.962, 0.959, 0.825 （and0.812, No）, 0.963, 0.289, and 0.095, respectively （r0.05 = 0.369, r0.01 = 0.505）. In conclusion, excluding the soil initial nitrate, the correlation coefficients between the eight methods and crop uptake N were, from high to low, N0, aerobic incubation for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks, and long-term alternate leaching aerobic incubation, while including the soil initial nitrate the correlation coefficients between them increased significantly and the values were all beyond 0.950 for these four methods, including aerobic incubation for 2 weeks and for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks and short-term leaching aerobic incubation. The waterlogged incubation method, Bc and BN in the calcareous soil, had lower correlation coefficient with crop uptake nitrogen compared with other methods. Thus, dry-wet alternation aerobic incubation for 2 weeks was a better index for evaluating calcareous soil N supply capacity due to some other methods having disadvantages and not suitable for the actual farmland characteristics.

A Review on the Precise Control of the Liquid Nitrogen Supplying System in Transonic Cryogenic Wind Tunnel

The liquid nitrogen(LN2)supplying system,one of the four key systems of the cryogenic wind tunnel(CWT),is an essential guarantee for the precise control,fast and safe regulation of the wind tunnel’s total temperature.Firstly,the technical schemes,advantages and disadvantages of different LN2 supplying systems are discussed and analyzed based on the operation conditions and test requirements of different CWTs.Then,together with the development of the pilot cryogenic transonic wind tunnel(PCTW),the key technologies of the system,including the supplying mode,rapid and accurate regulation of injection pressure,development of large scale cryogenic centrifugal pump,and matching technology between pumps and pipe network,have been summarized and the solutions to the existing issues are given.Finally,a supplying process suitable for large-scale CWT is proposed,which has the ability of independent commissioning,rapid regulation,accurate control of injection pressure and transient response to the wind tunnel’s wide range of working conditions.The breakthrough in LN2 supplying system enables China to construct a CWT for the future competitive high Reynolds number aircraft.

Effect of vegetation type, wetting intensity, and nitrogen supply on external carbon stimulated heterotrophic respiration and microbial biomass carbon in forest soils

By using packed soil-core incubation experiments, we have studied stimulating effects of addition of external carbon （C） （glu- cose, 6.4 g C m 2） on heterotrophic respiration and microbial biomass C of a mature broadleaf and Korean pine mixed forest （BKPF） and an adjacent white birch forest （WBF） soil under different wetting intensities （55% and 80% WFPS, water-filled pore space） and nitrogen （N） supply （NH4C1 and KNO3, 4.5 g N m-e） conditions. The results showed that for the control, the cumulative carbon dioxide （CO2） flux from WBF soil during the 15-day incubation ranged from 5.44 to 5.82 g CO2-C m-2, which was significantly larger than that from BKPF soil （2.86 to 3.36 g CO2-C m 2）. With increasing wetting intensity, the cumulative CO2 flux from the control was decreased for the WBF soil, whereas an increase in the CO2 flux was observed in the BKPF soil （P 〈 0.05）. The addition of NH4C1 or KNO3 alone significantly reduced the cumulative CO2 fluxes by 9.2%-21.6 % from the two soils, especially from WBF soil at low wetting intensity. The addition of glucose alone significantly increased soil heterotrophic respiration, microbial biomass C （MBC）, and microbial metabolic quotient. The glucose-induced cumulative CO2 fluxes and soil MBC during the incubation ranged from 8.7 to 11.7 g CO2-C m-2 and from 7.4 to 23.9 g C m-2, which are larger than the dose of added C. Hence, the addition of external carbon can increase the decomposition of soil native organic C. The glucose-induced average and maximum rates of CO2 fluxes during the incubation were significantly in- fluenced by wetting intensity （WI） and vegetation type （VT）, and by WIxVT, NH4ClxVT and WIxVTxNH4C1 （P〈0.05）. The addition of NH4C1, instead of KNO3, significantly decreased the glucose-induced MBC of WBF soil （P〈0.05）, whereas adding NH4C1 and KNO3 both significantly increased the glucose-induced MBC of BKPF soil at high moisture （P〈0.05）. According to the differences in soil labile C pools, MBC and CO2 fluxes in the presence and absence of glucose, it can be concluded that the stimulating effects of glucose on soil heterotrophic respiration and MBC under temperate forests were dependent on vegetation type, soil moisture, and amount and type of the N added.

Effect of Nitrogen Supply on the Nitrogen Use Efficiency of an Annual Herb, Helianthus annuus L.

Abstract: Nitrogen use efficiency (NUE) is the product of nitrogen productivity (NP) and the mean residence time of nitrogen (MRT). Theory suggests that there should be a trade-off between both components, but direct experimental evidence is still scarce. To test this hypothesis, we analyzed the effect of varying nitrogen supply levels on NUE and its two components (NP, MRT) in Helianthus annuus L., an annual herb. The plants investigated were subjected to six nitrogen levels (0, 2, 4, 8, 16, and 32 g N/m2). Total plant production increased substantially with increasing nitrogen supply. Nitrogen uptake and loss also increased with nitrogen supply. Nitrogen influx (rin) and outflux (rout) were defined as the rates of nitrogen uptake and loss per unit aboveground nitrogen, respectively. Both rm and rout increased with increasing nitrogen supply. In addition, rm was far higher than rout. Consequently, the relative rate of nitrogen increment (rin-rout) also increased with nitrogen supply. There were marked differences between treatments with respect to parameters related to the stress resistance syndrome: nitrogen pool size, leaf nitrogen concentration, and net aboveground productivity increased with nitrogen supply. Plants at high nitrogen levels showed a higher NP (the growth rate per unit aboveground nitrogen) and a shorter MRT (the inverse of rout), whereas plants at low nitrogen levels displayed the reverse pattern. Shorter MRT for plants at high nitrogen levels was caused by the abscission of leaves that contained relatively large fractions of total plant nitrogen. We found a negative relationship between NP and MRT, the components of NUE, along the gradient of nitrogen availability, suggesting that there was a trade-off between NP and MRT. The NUE increased with increasing nitrogen availability, up to a certain level, and then decreased. These results offer support for the hypothesis that adaptation to infertile habitats involves a low nitrogen loss (long MRT in the plant) rather than a high NUE per se. The higher NUE at the plant level was a result, in part, of greater nitrogen resorption during senescence. We suggest that a long MRT (an index of nitrogen conservation) is a potentially successful strategy in nitrogen-poor environments.