Responses Of Nitrogen Use Efficiency Research Articles

Response of nitrogen use efficiency, N-assimilating enzymes and growth in Cyclocarya paliurus seedlings to different nitrogen nutrition

Cyclocarya paliurus has been used as tea production and medicine in China. In order to identify C. paliurus preference for absorption of nitrogen (N) nutrition and the relationship between C/N ratio and growth, effects of five NO3 −/NH4 + ratio treatments on growth, N absorption and metabolism of C. paliurus seedlings were investigated. Compared to NH4 + as a sole N source, the seedlings supplied with a sole NO3 − source had higher growth rate, percent of nitrogen derived from nitrogen fertilizer (NDFF), N content and nitrogen use efficiency (NUE). However, mixed nitrate-ammonium nutrition improved growth and NUE in C. paliurus seedling, while an equal mixed ratio nutrition induced the highest NDFF and seedling growth. Nitrate reductase (NR) and nitrite reductase (NiR) activities in leaves and roots showed a decreased trend with decreasing NO3 − in growth medium, whereas the highest glutamine synthetase (GS) and glutamate synthase (GOAGT) activities were detected at the equal mixed ratio of NO3 −/NH4 +. Regression analysis showed that activities of the N-assimilated enzymes were positively correlated with NUE and N content in C. paliurus seedlings, but the seedling growth was negatively and significantly correlated with C/N ratio. Our study demonstrated that C. paliurus preferred NO3 − over NH4 + in N nutrition, but an equal mixed ratio of NO3 −/NH4 + would best improve seedling growth and nitrogen use efficiency. This study would provide a basis for manipulating nitrogen fertilization in C. paliurus plantations.

338 Nitrogen Use Efficiency Is Proportionally More Improved When Young Bulls Are Ranked on Residual Body Gain Rather Than on Residual Feed Intake

Abstract Animals with superior feed efficiency (FE) may also have an improved nitrogen use efficiency (NUE), which would be beneficial to economic profitability while reducing environmental impacts. When genetically selecting animals on FE, it is preferable to use residual traits [e.g. residual feed intake (RFI) or residual body gain (RG)] rather than ratios because of their predictable genetic outcomes. We studied the relationship of RFI and RG with NUE, estimated from the validated 15N abundance in plasma, across two contrasted diets based on corn or grass silages. We evaluated FE of 588 (half by diet) Charolais bulls (545 ± 57 kg BW) from 12 experimental cohorts (different farms and periods) over 200 days. Before the end of the FE test, plasma was sampled and analyzed for δ 15N. NUE was related to FE through simple-linear models with variables previously corrected for the cohort and diet effects. The models’ slopes were standardized according to FE deviation in order to compare the response of NUE to FE between indices. Higher NUE was related to higher FE (P < 0.001), showing positive correlations with RG (r=-0.40) and negative with RFI (r=0.29). However, the standardized slope of NUE to RG was significantly higher (+28%; P < 0.05) than that of NUE to RFI. This stronger NUE relation to RG compared to RFI could reflect a higher potential of RG animals to deposit N as compared to a more conservational N metabolism in RFI individuals. Regarding diets, and despite the correction of NUE and FE for this effect, the slopes of NUE to FE were numerically (P > 0.05) higher (-16% and +36%; for RG and RFI) in corn-based diets, which agrees with superior NUE observed in corn-vs-grass diets. Results suggested that superior RG animals may present proportionally higher NUE than superior RFI animals, with even better results in corn-vs-grass diets.

Effects of increasing fertilization rates on nitric oxide emission and nitrogen use efficiency in low carbon calcareous soil

Global nitrogen fertilizer consumption is expected to continue to increase. To explore effective mitigation strategies, a deeper understanding of the responses of nitrogen use efficiency, nitric oxide (NO) emission and the NO direct emission factor (EFd) to increasing fertilization rates is needed. A gradient of fertilization rates (0, 135, 270, 430, 650 and 850kgNha−1yr−1 in the form of urea, hereafter referred to as N0, N135, N270, N430, N650 and N850, respectively) was used to fully represent the nitrogen application levels in the wheat–maize rotational cropping system that has been widely adopted in China. The annual NO emissions ranged from 0.43±0.04 (N0) to 2.64±0.35kgNha−1yr−1 (N850) and linearly increased with increasing fertilization rates (P<0.01). The high pH and low carbon availability in the calcareous soil limited NO production; thus, low EFd values (0.26–0.36%) were observed. The partial factor productivity of applied nitrogen (PFPN) rapidly decreased with increasing fertilization rates; the relationship could be characterized by a rectangular hyperbolic function (P<0.01). The expected trade-off between EFd and PFPN was not observed. The on-farm PFPN was only 33±3kggrainkg−1N (N430), highlighting the necessity of optimizing current management strategies. Based on a review of previous studies, a comprehensive optimized management strategy is recommended to obtain the maximum benefits for multiple goals of a wheat–maize cropping system. However, consecutive field observations and model studies are still needed to validate the long-term effects of this management strategy.

Response of nitrogen use efficiency and soil nitrate dynamics to soil mulching in dryland maize (Zea mays L.) fields

Plastic film (FM) and gravel mulching (GM) have been used extensively to increase dryland agricultural productivity. Understanding mulching effects on nitrogen (N) use efficiency (NUE) and soil nitrogen dynamics is important for optimizing N management strategies. A 3-year field experiment was performed on the Loess Plateau of China to investigate the GM and FM effects on plant N accumulation, N translocation, N harvest index (NHI), NUE and soil NO3 −-N dynamics in dryland maize fields. Compared with the control (CK, non-mulching), the mulching treatments markedly promoted plant N accumulation and especially maintained higher N uptake rates during the post-silking stage. At harvest, the total N accumulation was 12.8–41.2 and 33.2–55.8 % higher in the GM and FM treatments, respectively, than in the CK treatment. The NHIs of the mulching treatments were significantly higher by 9.6–32.4 % than the CK treatment, primarily due to greater N translocation and N accumulation post-silking. Overall, compared with the CK treatment, the GM and FM NUEs increased significantly by 17.1 and 28.3 % in 2010, 70.3 and 87.6 % in 2011, and 16.7 and 38.2 % in 2012, respectively. In the wet years of 2010 and 2011, the increased amount of soil NO3 −-N in the 100–200 cm layer after harvest was 27.1–57.1 and 47.9–85.7 % lower in the GM and FM treatments, respectively, than in the CK treatment, indicating a lower NO3 −-N leaching loss. These results suggest that mulching (especially FM) is an effective measure for increasing NUE and grain yield and decreasing N leaching loss in dry farmland.

Response of Nitrogen Use Efficiency to Plant Density and Nitrogen Application Rate for Maize Hybrids from Different Eras in Heilongjiang Province

In this study, eight typical maize hybrids released from 1970s to 2000s in Heilongjiang Province were selected to investigate the responses of grain yield, nitrogen (N) partial factor productivity (PFP), N agronomic efficiency (NAE) and N recovery efficiency (NRE) to N application rate and plant density in 2009 and 2010. During the variety improvement period of 1970s–2000s, PFP and NRE increased significantly by 3.41 kg kg–110 yr–1and 2.26 percent 10 yr–1, respectively. NAE increased significantly from 1970 to 1990 and descended after 1990. N harvest index decreased significantly by 1.51 per cent 10 yr–1. Grain N, stem N and leaf N accumulations rose significantly by 0.09, 0.07, and 0.12 g plant–110 yr–1. There were significant interactions among eras, plant densities and N application rates for above indicators. Nitrogen use efficiency exhibited decline trends with increasing N application rate and parabolic shape response to increasing plant density, and got the maximum in the population range of 50 000–70 000 plants ha–1. The theoretical optimal plant density for the maximal NUE was higher in newer hybrids than in the older ones. Higher plant population led to decrease N accumulation and N harvest index in grain, stem and leaf for all hybrids from different eras. Higher N application rate tended to promote N accumulation in grain, stem and leaf, but had different effects on N harvest index for hybrids from different eras. Compared to the varieties released abroad, there is a great potential in maize variety improvement for high-yield and high-NUE in Northeast China. According to the existing variety’s traits, increasing plant density can enhance not only maize yield but also NUE.