Establishment of Critical Nitrogen Concentration Models in Winter Wheat under Different Irrigation Levels

The aim of this study was to verify the applicability of the critical nitrogen concentration dilution curve (Nc) of wheat grown under different irrigation conditions in the field, and discuss the feasibility of using the N nutrition index (NNI) to optimize N fertilizer application. The high-yield, medium-protein wheat varieties Zhoumai 27 and Zhoumai 22 were used in field experiments in two different locations (Zhengzhou and Shangshui) in Huang-Huai, China. Plants were grown under rainfed and irrigation conditions, with five N application rates. Nc models of the leaves, stems, and whole plant were constructed, followed by establishment of an NNI model and accumulative N deficit model (Nand). As previous research reported, our results also showed that the critical N concentration and biomass formed a power function relationship (N = aDW−b). When the biomass was the same, the critical N concentration was higher under irrigation than rainfed treatment. Meanwhile, the fitting accuracy (R2) of the Nc model was also higher under irrigation than rainfed treatment in both sites, and was higher in the stems and whole plant. The NNI calculated using the Nc model increased with increasing N application, reflecting N deficiency. Moreover, there was a significant negative linear correlation between NNI and Nand, and both indices could be uniformly modeled between locations and water treatments. The accuracy of the Nand model was highest in the whole plant, followed by the leaves and stems. The models constructed in this paper provide a theoretical basis for accurate management of N fertilizer application in wheat production.

Growth, Critical N Concentration and Crop N Demand in Butterhead and Crisphead Lettuce Grown under Mediterranean Conditions

Excessive nitrogen (N) fertilizers are applied in lettuce causing both environmental issues and N crop luxury consumption. In order to improve the N use efficiency (NUE) by defining optimal crop growth and N requirements of butterhead and crisphead lettuce, two field experiments were conducted using 0, 50, and 100 kg ha−1 of N fertilizer to study (i) the growth and productivity, (ii) the NUE, (iii) the critical N dilution curve, and (iv) the N demand. Nitrogen supply enhanced dry weight (DW) accumulation in the butterhead (from 295 to 410 g m−2), but not in the crisphead type (251 g m−2). The NUE indices underlined the poor ability of the crisphead type in absorbing soil N and also in the utilization of the absorbed N for producing DW. The critical N dilution curves %Nc = 3.96 DW−0.205 and %Nc = 3.65 DW−0.115 were determined for crisphead and butterhead lettuce, respectively. Based on these type-specific %Nc curves, the estimated N demand was 125 kg ha−1 in the butterhead and 80 kg ha−1 in the crisphead lettuce for producing 4.3 and 2.5 Mg ha−1 of DW, respectively, under Mediterranean climate. Neither N fertilization nor genotype affected crop productivity.

Nitrogen-limited light use efficiency in wheat crop simulators: comparing three model approaches

SUMMARYThree different explanatory indicators for reduced light use efficiency (LUE) under limited nitrogen (N) supply were evaluated. The indicators can be used to adapt dry matter production of crop simulators to N-limited growth conditions. The first indicator, nitrogen factor (NFAC), originates from the CERES-Wheat model and calculates the critical N concentration of the shoot as a function of phenological development. The second indicator, N nutrition index (NNI), calculates a critical N concentration as a function of shoot dry matter. The third indicator, specific leaf nitrogen (SLN) index (SLNI), has been newly developed. It compares the actual SLN with the maximum SLN (SLNmax). The latter is calculated as a function of the green area index (GAI). The comparison was based on growth curves and fitted to empirical data, and was carried out independently from a dynamic crop model. The data set included four growing seasons (2004–2006, 2012) in Northern Germany and seven modern bread wheat cultivars with varying N fertilization levels (0–320 kg N/ha). The influence of N shortage on LUE was evaluated from the beginning of stem elongation until flowering. With the exception of 2005, the highest productivity was observed for the highest N level. A moderate N shortage primarily reduced GAI and therefore light interception, while LUE remained stable under moderate N shortage. The relative LUE (rLUE) of a specific day was defined as the ratio of actual to maximal LUE. None of the indicators was proportional to rLUE, but the relationships were described well by quadratic plateau curves. The correlation between simulated and measured rLUE was significant for all explanatory indicators, but different in terms of mean absolute error and coefficient of determination (R2). The performance of SLNI and NNI was similar, but the goodness of prediction was much lower for NFAC. Compared with NNI and NFAC, SLNI corresponded to leaf N and was therefore sensitive to N translocation from leaves to growing grains during the reproductive stage. For this reason, SLNI may have the potential to improve simulation of dry matter production in wheat crop simulators.

A new approach for determining rice critical nitrogen concentration

SUMMARYA reliable evaluation of crop nutritional status is crucial for supporting fertilization aiming at maximizing qualitative and quantitative aspects of production and reducing the environmental impact of cropping systems. Most of the available simulation models evaluate crop nutritional status according to the nitrogen (N) dilution law, which derives critical N concentration as a function of above-ground biomass. An alternative approach, developed during a project carried out with students of the Cropping Systems Masters course at the University of Milan, was tested and compared with existing models (N dilution law and approaches implemented in EPIC and DAISY models). The new model (MAZINGA) reproduces the effect of leaf self-shading in lowering plant N concentration (PNC) through an inverse of the fraction of radiation intercepted by the canopy. The models were tested using data collected in four rice (Oryza sativaL.) experiments carried out in Northern Italy under potential and N-limited conditions. MAZINGA was the most accurate in identifying the critical N concentration, and therefore in discriminating PNC of plants growing under N-limited and non-limited conditions, respectively. In addition, the present work proved the effectiveness of crop models when used as tools for supporting education.

Controlled Elasticity in Nano-Structured Metallic Glass by Ion Implantation Method

Different reactivity of ions has been implanted into Zr-Cu metallic glass to obtain nano-structured surface with controlled elasticity. The penetration of glass forming element of Ni+ into crystalline Zr-Cu stabilizes glassy phase to induce crystalline-amorphous (c-a) transition during implantation process. In the meanwhile, penetration of N+ into glassy matrix induces precipitation of (Zr, Cu)N at the mean penetration depth of N. Critical N concentration for nitride formation is estimated to be (Zr,Cu)-20at%N, which also suggests existing of N solid solution of glassy phase. Inert element of Ar+ yields dispersion of nano-voids among glassy matrix. Nano-indentation tests reveal that Young’s modulus of ion implanted glassy film dramatically changes with respect to the induced nano-structure, to decrease 0.4 times for Ar+, to increase 1.3 times for N+ as comparison with that for as-deposited state.

Nitrogen Fertigation of Young Navel Oranges: Growth, N Status, and Uptake of Fertilizer N

Microsprinkler irrigation may result in increased efficiency of N and water application to citrus. However, best management practices (BMPs) have not yet been developed for microsprinkler use, particularly on newly established citrus. Experiments were conducted during 1997-98 in central Arizona to evaluate the effects of N rate and fertigation frequency on `Newhall' navel oranges (Citrus sinensis) planted in Mar. 1997. Two experiments were conducted, each with factorial combinations of N rate (0 to 204 g/tree/year) and fertigation frequency (weekly to three times per year). In one experiment, nonlabeled N fertilizer was used, and in the other 15N-labeled fertilizer was used. Trunk diameter, leaf N, and 15N partitioning in the trees were monitored. During 1997, neither trunk diameter nor leaf N were affected by N rate or fertigation frequency. No more than 6% of N applied was found in the trees. During 1998, leaf N in fertilized plots was significantly higher than in nonfertilized plots, but leaf N in all trees remained above the critical N concentration of 25 mg·g-1. During 1998, no more than 25% of the fertilizer N applied was taken up by the trees. Results suggest that N applications are not needed during the first growing season after planting for microsprinkler-irrigated citrus in Arizona. Only low rates of N (≤68 g/tree/yr) may be needed during the second growing season to maintain adequate tree N reserves.

Nitrogen utilization by forage grasses

The efficient utilization of nitrogen (N) in grass production is essential to reduce the risks of water and air pollution, and the costs of production. Recent findings in grass physiology and agronomy should help in developing new tools to improve N utilization efficiency. A model of N dilution describing the decrease in plant N concentration with increasing shoot biomass under non-limiting N supply is used to define a critical N concentration in grasses required to reach maximum shoot growth and yield. The index of N nutrition (INN) is then calculated as the measured N concentration in a given situation divided by the critical N concentration. The INN is a diagnostic tool to quantify the level of N deficiency during growth cycles, and can also be used in crop modelling and in the interpretation of results from studies conducted over many sites and years. The "universality" of the model of N dilution is based on the increased proportion of structural to metabolic components during crop growth combined with the fact that the structural component has a lower N concentration. Inter- and intra-species differences in N concentration at a given shoot biomass can be related to differences in the proportion of leaves which are assumed to be equivalent to the metabolic component. Under N-deficient conditions, the reduction in grass growth is due to a reduction in the interception of solar radiation primarily through reduced leaf extension, and to a reduction in the conversion efficiency of intercepted radiation into shoot biomass primarily through an effect on biomass partitioning between roots and shoots. The concept of the critical N concentration based on the relationship between plant N concentration and shoot biomass is used to derive general and synthetic expressions of the effect of plant N nutrition on crop growth and crop growth processes. These recent findings on the relationship between N nutrition and the growth of forage grasses should result in the improvement of the efficiency of N utilization by a more precise fertilizer management and the development of more N efficient cultivars. Key words: Physiology, growth, photosynthesis, leaf, partitioning, model

Angle-Resolved XPS Studies of Interfacial Bonding States in Silicon oxynitrides Fabricated Using Different Thermal Methodologies

ABSTRACTSilicon oxynitride films, fabricated by direct thermal growth and annealing in N2O or NO, were analyzed by Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS). It is seen that for the samples processed in N2O, N is bonded as Si3N4 only, irrespective of whether the fabrication was done on bare Si or on an oxide pre-grown in O2. But the films processed in NO depict additional bonding arrangements, namely, non-stoichiometric SiOxNy, (Si-)2-N-O, and Si-N(-O)2. These bonding states are found to be concentrated in a higher proportion above the oxynitride/substrate interface. Further, it is seen that annealing of a pre-grown oxide in NO for 30 min incorporates the same bonding states as by direct growth in NO for as long as 120 min. Also, a critical N concentration (between 1.9% and 2.3%) is required for the incorporation of the Si-N(-O)2 structure, observed at 400.7 eV. Besides enhancing the overall understanding of the progress of silicon oxynitridation process in N2O and NO, these findings can help significantly towards developing process-property relationships for incorporation of N with the desired bonding state(s) at specific positions within an oxynitride film.