Published in Agron J 100:271-276 (2008)
DOI: 10.2134/agrojnl2007.0059
© 2008 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
NITROGEN MANAGEMENT
Critical Nitrogen Curve and Nitrogen Nutrition Index for Corn in Eastern Canada
Noura Ziadia,*,
Marianne Brassarda,
Gilles Bélangera,
Athyna N. Cambourisa,
Nicolas Tremblayb,
Michel C. Nolina,
Annie Claessensa and
Léon-Étienne Parentc
a Agriculture and Agri-Food Canada (AAFC), Soils and Crops Research and Development Centre, 2560 Hochelaga Blvd., Quebec, QC, Canada G1V 2J3
b AAFC, 430 Gouin Blvd., St-Jean-sur-Richelieu, QC, Canada J3B 3E6
c Dep. of Soil and Agri-Food Engineering, Laval Univ., Sainte-Foy, QC, Canada G1V 0A6
* Corresponding author (ziadin{at}agr.gc.ca).
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ABSTRACT
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Plant-based diagnostic methods of N nutrition require the critical N concentration (Nc) to be defined, that is the minimum N concentration necessary to achieve maximum growth. A critical N curve (Nc = 34.0W–0.37 with W being shoot biomass in Mg DM ha–1), based on whole plant N concentration, was determined for corn (Zea mays L.) in France. Our objectives were to validate this critical N curve in eastern Canada and to assess its plausibility to estimate the level of N nutrition in corn. Shoot biomass and N concentration were determined weekly during the growing season at three sites for 2 yr (2004 and 2005); four to seven N treatments were used at each site. Data points were divided into two groups representing either nonlimiting or limiting N conditions according to significant differences in shoot biomass at each sampling date. All data points included in the limiting N group were under the critical N curve and most data points of the nonlimiting N group were on or above the critical N curve, hence confirming the validity of the critical N curve determined in France. The nitrogen nutrition index (NNI), calculated as the measured N concentration divided by the predicted Nc, ranged from 0.30 to 1.35. A significant relationship between relative grain yield (RY) and NNI (RY = –0.11 + 1.17 NNI if NNI < 0.93 and RY = 0.98 if NNI > 0.93; R2 = 0.89) was determined. The critical N curve from France is valid in eastern Canada and the NNI calculated from that curve is a reliable indicator of the level of N stress during the growing season of corn.
Abbreviations: CHU, corn heat units • DM, dry matter • LSD, least significant difference • NNI, nitrogen nutrition index • SEM, standard error of the mean
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NOTES
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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
Received for publication February 9, 2007.
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INTRODUCTION
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PLANT-BASED DIAGNOSTIC METHODS of N nutrition, which are used to adjust the N input to crops, require the critical N concentration (Nc) to be defined, that is the minimum N concentration required for maximum crop growth rate (Ulrich, 1952). These diagnostic methods can be based on the N concentration of specific plant parts (e.g., leaves, petioles) or of whole plants. The concept of a critical N curve based on the N concentration for whole plants was first developed by Lemaire and Salette (1984) for tall fescue (Festuca arundinacea Schreb.) and has been successfully applied to wheat (Triticum aestivum L.) (Justes et al., 1994), rapeseed (Brassica napus L.) (Colnenne et al., 1998), potato (Solanum tuberosum L.) (Greenwood et al., 1990; Duchenne et al., 1997; Bélanger et al., 2001), rice (Oryza sativa L.) (Sheehy et al., 1998), grain sorghum (Sorghum bicolor L.) (van Oosterom et al., 2001), and corn (Plénet and Lemaire, 2000; Herrmann and Taube, 2004).
The Nc is represented by an allometric function:
 | [1] |
where W is the total shoot biomass expressed in Mg DM ha–1, Nc is the total N concentration in shoots expressed in g kg–1 DM, and a and b are estimated parameters. The parameter a represents the N concentration in the total shoot biomass with 1 Mg DM ha–1 and the parameter b represents the coefficient of dilution which describes the relationship of decreasing N concentration with increasing shoot biomass. However, during the early stages of growth (biomass < 1 Mg DM ha–1), Nc takes a constant value due to the small decline of Nc with increasing shoot biomass (b = 0.12–0.15) and the lack of competition for light of isolated plants (Lemaire and Gastal, 1997). Above the threshold of 1 Mg DM ha–1, Plénet and Lemaire (2000) in France estimated the parameters (a = 34.1 and b = 0.37) in this allometric function for corn using approximately weekly sampling up to 25 d after silking. Herrmann and Taube (2004) in Germany confirmed the critical N curve of Plénet and Lemaire (2000) with similar parameters (a = 34.1 and b = 0.39) and extended its range to silage maturity. However, variation in the N critical curve between and within species (Justes et al., 1994; Bélanger et al., 2001), and between experimental sites (Greenwood et al., 1990) have been reported. A validation of these parameters for the pedo-climatic conditions and corn hybrids of eastern Canada is therefore required.
Our objectives were to validate the parameters of the critical N curve of Plénet and Lemaire (2000) for corn hybrids in eastern Canada and to assess the plausibility of using this critical N curve to estimate the level of N nutrition in corn.
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MATERIALS AND METHODS
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Site Description and Treatments
Measurements to validate the parameters of a critical N curve (Plénet and Lemaire, 2000) and to estimate the NNI were taken at three sites in each of 2 yr (2004 and 2005) within Quebec, Canada: St-Louis (45°51' N, 73°00' W), St-Basile-de-Portneuf, referred to as St-Basile (46°48' N, 71°46' W), and L'Acadie (45°17' N, 73°20' W) in 2004; and St-Louis, Ste-Catherine-de-la-Jacques-Cartier, referred to as Ste-Catherine (46°49' N, 71°39' W), and L'Acadie in 2005. At St-Louis and L'Acadie, different fields were used in 2004 and 2005. These sites represent three different soil textures with different crop histories. Site characteristics and cropping practices are provided in Table 1
. Organic matter content was determined by wet oxidation (Tiessen and Moir, 1993). Soil pH was measured in distilled water with a 1:2 soil/solution ratio (Hendershot et al., 1993). Particle size analysis was performed by the hydrometer method after oxidizing the organic matter (Sheldrick and Wang, 1993). Precipitation and temperature data were collected by Environment Canada at the Fleury station (45°48' N, 73°00' W) for the St-Louis sites, at the Ste-Christine-de-Portneuf station (45°49' N, 71°55' W) for the St-Basile and Ste-Catherine sites, and at the L'Acadie station (45°17' N, 73°21' W) for the L'Acadie sites. Corn hybrids and planting and fertilization dates were specific to each site (Table 1).
Six N application rates (20, 50, 100, 150, 200, and 250 kg N ha–1) with a split application and one N rate (250s kg N ha–1) with a single application at planting were compared, except at L'Acadie where only four N rates (20, 73, 125, and 178 kg N ha–1 in 2004 and 30, 83, 135, and 188 kg ha–1 in 2005) with a split application were compared. The 250s kg N ha–1 treatment received 250 kg N ha–1 at planting as 11–52–0 and 27–0–0. All other plots received 20 kg N ha–1 as 11–52–0 and 34–0–0 applied at planting, except at L'Acadie in 2005 where 30 kg N ha–1 was applied. At either the V8 or V10 stage of development (Table 1), a second N application as calcium ammonium nitrate (27–0-0) was banded by hand 10 cm from the corn plant at the desired N application rates for each plot. At planting, P and K fertilizers were applied according to soil analysis and local recommendations (Centre de Références en Agriculture et Agroalimentaire du Québec, 2003). Thus, 35 kg P ha–1 and 35 kg K ha–1 in 2004, and 35 kg P ha–1 and 50 kg K ha–1 in 2005, were mechanically applied at each site. Treatments were arranged in a randomized complete block design with four replications at each experimental site. The plot size was 9 by 10 m and consisted of 12 corn rows, except at L'Acadie where plot size was 6 by 10 m with eight corn rows. A 0.75-m interrow spacing was used. The plant density was approximately 79,040 plants ha–1.
Sample Collection and Analysis
Shoot biomass was sampled weekly for 8 wk in 2004 and 7 wk in 2005 using a 2-m row section in each plot. We excluded data from the sampling dates for which the shoot biomass was <1.0 Mg DM ha–1 (Table 2
). Whole plants were cut at ground level using pruning-scissors. Shoot biomass was weighed fresh and subsamples were collected for DM determination and laboratory analyses. At St-Louis, St-Basile, and Ste-Catherine, subsamples consisted of five plants randomly selected within a 2-m row section; at L'Acadie, all plants from the 2-m row section were mechanically shredded and a subsample of approximately 500 g was collected. Subsamples were dried at 55°C in a forced-draft oven for 7 d, ground to pass through a 1-mm screen in a Wiley mill, and stored at room temperature before laboratory analyses. Samples of 0.1 g of dried and ground corn were mineralized using a mixture of sulfuric and selenious acids, as described by Isaac and Johnson (1976), and N was measured on a QuikChem 8000 Lachat autoanalyzer using the Lachat method 15–501–3 (Lachat Instruments, 2005). Grain yield was determined in each plot by harvesting whole plants manually from a 10 by 0.75-m area (Table 1). Harvested ears were wet shelled and a grain subsample was dried at 55°C until the weight stabilized; grain yield was adjusted to 14% moisture.
Data Analysis
Data of shoot biomass and N concentration for each sampling date, site, and year were subjected to analyses of variance using the PROC GLM (SAS Institute, 2001) and standard errors of the means (SEM) were calculated; data of N concentration and SEM values were reported previously (Ziadi et al., 2007). To validate the parameters of the critical N curve of Plénet and Lemaire (2000), data representing limiting and nonlimiting N conditions were determined using the analysis of variance and a LSD test (SAS Institute, 2001) with a similar method to that of Greenwood et al. (1990). Sampling dates were not used in determining the critical N curve if the analysis of variance (F-values) indicated no significant (P 
0.10) differences among N application rates (Table 2). For the remaining sampling dates, treatments were classified using the LSD test. Treatments with significantly (LSD0.10) lower shoot biomass were considered to be limiting while treatments with significantly (P 0.10) higher shoot biomass were considered to be nonlimiting; treatments were not included if their shoot biomass was classified in more than one group.
The NNI of the crop at each sampling date was determined by dividing the N concentration of the shoot biomass by Nc, an approach previously used on tall fescue (Bélanger et al., 1992), timothy (Bélanger and Richards, 1997), and potato plants (Bélanger et al., 2001). The minimum N concentration required to achieve maximum shoot growth, Nc, was defined as a function of shoot biomass as proposed for corn by Plénet and Lemaire (2000; Nc = 34.0 x W–0.37 with W being shoot biomass in Mg DM ha–1). The relative yield was calculated as the ratio of the grain yield obtained for a given N rate with the highest grain yield among all N application rates; values of relative yield were reported previously (Ziadi et al., 2007). The relative yield was then expressed as a function of NNI and the quadratic function was estimated using SAS (SAS Institute, 2001).
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RESULTS AND DISCUSSION
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Shoot Biomass and Nitrogen Concentration
Shoot biomass during the growing season ranged from 1.0 to 12.1 Mg DM ha–1, depending on N application rates, sampling date, site, and year (Table 2). Shoot biomass generally increased with increasing N fertilization, although this effect was not always statistically significant.
Nitrogen concentration in the shoot biomass decreased during the growing season (Fig. 1
; Ziadi et al., 2007). Decreased N concentration with time, or advancing maturity, has been reported for wheat (Justes et al., 1994), potato (Duchenne et al., 1997), timothy (Bélanger and Richards, 1997; 1999), and corn (Plénet and Lemaire, 2000). This decline in N concentration with time, or increasing biomass, is attributed to a decrease in the fraction of total plant N associated with photosynthesis in relation to a concomitant increase in the N fraction of structural and storage constituents (Caloin and Yu, 1984; Lemaire et al., 1992; Lemaire and Chartier, 1992; Bélanger and Gastal, 2000). Nitrogen concentrations varied from a maximum of 38.7 g kg–1 DM at St-Louis on 6 July 2004 to a minimum of 6.1 g kg–1 DM observed at St-Basile on 20 Aug. 2004. A similar range of N concentration (7–34 g N kg–1 DM) was reported by Plénet and Lemaire (2000) for corn grown with different N application rates in France. They attributed the low N concentration observed at the early period of ear growth to cell division and expansion.
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Fig. 1. Changes in N concentration as a function of thermal time (cumulative corn heat units, CHU) of corn fertilized with various N application rates in an experiment conducted at three sites in each of 2 yr (2004 and 2005). Vertical bars represent LSD values (P 0.10) at each sampling date; ND: LSD was not determined. 250s indicates 250 kg N ha–1 applied at planting.
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Validation of Critical Nitrogen Curve for Corn
Data points for the different N application rates were characterized as representing limiting (20 data points) or nonlimiting (24 data points) growing N conditions; this characterization was based on significant (P 0.10) differences in shoot biomass at each sampling date, site, and year. In general, the critical N curve of Plénet and Lemaire (2000) discriminated between the limiting and nonlimiting N conditions (Fig. 2
). All data points identified as limiting N conditions, except one, were under the critical N curve of Plénet and Lemaire (2000) and most data points identified as nonlimiting N conditions were above or near the critical N curve of Plénet and Lemaire (2000).
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Fig. 2.  Validation of the critical N curve using data from corn grown under limiting and nonlimiting N growing conditions. Solid line, critical N curve (Nc = 34.0W–0.37) describes the relationship between the critical N concentration and shoot biomass of corn in France (Plénet and Lemaire, 2000); dashed line, critical N curve (Nc = 34.1W–0.391) describes the relationship between the critical N concentration and shoot biomass of corn in Germany (Herrmann and Taube, 2004).
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In this study, different rates of N fertilization were applied during the growing season at the V8 to V10 stages of development, following a common application of 20 to 30 kg N ha–1 at planting. This in-season N was applied at 0 to 21 d before the first sampling date. Shoot biomass did not always differ significantly even when low N rates (i.e., 20–30 kg N ha–1 applied at planting followed by 20 kg N ha–1 applied at the V8–V10 stage of development) were compared with high N rates (i.e., 250 kg N ha–1). In some cases, our test could not detect significant differences in shoot biomass; the LSD (P 0.10) values were relatively high (0.2–1.55 Mg DM ha–1; Table 2).
The parameters a and b of the critical N curve of Plénet and Lemaire (2000) are similar to those obtained by Herrmann and Taube (2004) in Germany. These authors extended their study until silage maturity, whereas Plénet and Lemaire (2000) included data points from emergence up to 25 d after silking. These two sets of critical N curves from Europe appear to be robust and applicable to a wide range of environments and genotypes, including those of eastern Canada. Because our sampling period was similar to that of Plénet and Lemaire (2000), we suggest using their parameters for the critical N curve in eastern Canada.
Nitrogen Nutrition Index
The critical N curve, defined by Eq. [1], discriminates three different types of N status (Colnenne et al., 1998). Data points below the curve indicate situations where N is limiting growth, whereas data points above the curve indicate situations of excessive N nutrition. Data points located on or near the curve correspond to situations where N does not limit growth and N nutrition is not excessive. We used the critical N curve of Plénet and Lemaire (2000) to estimate the Nc at each sampling date and to calculate the NNI. Values of NNI 
1.0 indicate that the crop is in a situation of nonlimiting supply of N, whereas values of NNI smaller than 1.0 indicate N deficiency. For instance, at St-Louis in 2004, the data points with N applications of 20, 50, and 100 kg N ha–1 were generally smaller than 1.0, indicating that N was limiting growth (Fig. 3
). With 150 and 200 kg N ha–1, however, the data points were generally near 1.0, indicating that N was not limiting growth, and with 250 and 250s kg N ha–1 the data points were generally well above the critical N curve, indicating excessive N nutrition.
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Fig. 3. Nitrogen nutrition index (NNI) of corn fertilized with various N application rates in an experiment conducted at three sites in each of 2 yr (2004 and 2005). The NNI is presented for the different sampling dates expressed in cumulative corn heat units (CHU). Vertical bars represent LSD values (P 0.10) at each sampling date; ND: LSD was not determined. 250s indicates 250 kg N ha–1 applied at planting.
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The relationship between relative yield and NNI, expressed by a quadratic function, accounted for 90% of the variation. For a NNI 1.0, the relative yield was near 1.0 (Fig. 4
). With decreasing NNI below 1.0, the relative yield decreased. The model of Nc and the resulting NNI, therefore, adequately identified situations of deficient and nondeficient N nutrition in corn making it possible to quantify the level of corn N nutrition. A major difficulty in using the NNI at the farm level, however, is the need to determine the actual crop mass and its N concentration. We suggest that the NNI could be used as a reference for simpler procedures (e.g., chlorophyll measurements) to determine crop N status (Bélanger et al., 2003). The NNI has also been used in crop models to account for the effect of N on growth and yield of corn (Brisson et al., 1998) and other species (Bélanger et al., 2001).
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Fig. 4. Relationship between relative grain yield (RY) and the N nutrition index (NNI) of corn in an experiment conducted at three sites in each of 2 yr (2004 and 2005); data of NNI were averaged over all sampling dates.
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The NNI values in our study ranged from 0.30 to 1.35 (Fig. 3). Our results confirm the ability of corn to take up more N than required for maximum growth. In France, however, Plénet and Lemaire (2000) obtained some NNI values as high as 1.7. In eastern Canada, Bélanger et al. (2001) reported values ranging from 0.5 to 1.4 for potato.
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CONCLUSIONS
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We concluded that the critical N curve of Plénet and Lemaire (2000) can be applied to corn grown under the pedo-climatic conditions of eastern Canada. In addition, the NNI calculated from that curve is a reliable indicator of the level of N stress during the growing season.
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ACKNOWLEDGMENTS
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This study was funded by Synagri Inc. and Agriculture and Agri-Food Canada (AAFC) through a matching investment initiative program and the GAPS program of AAFC. The assistance of Alain Larouche, Mario Deschênes, Sylvie Michaud, Danielle Mongrain, Carl Bélec, Edith Fallon, and Marcel Tétreault is greatly appreciated.
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.
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TOP
ABSTRACT
INTRODUCTION
