Published in Agron J 100:80-86 (2008)
DOI: 10.2134/agrojnl2007.0119
© 2008 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
PHOSPHORUS MANAGEMENT
Relationship between Phosphorus and Nitrogen Concentrations in Spring Wheat
Noura Ziadia,*,
Gilles Bélangera,
Athyna N. Cambourisa,
Nicolas Tremblayb,
Michel C. Nolina and
Annie Claessensa
a Agriculture and Agri-Food Canada (AAFC), Soils and Crops Research and Development Centre, 2560 Hochelaga Blvd., Québec, QC, Canada G1V 2J3
b AAFC, 430 Gouin Blvd., St-Jean-sur-Richelieu, QC, Canada, J3B 3E6
* Corresponding author (ziadin{at}agr.gc.ca).
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ABSTRACT
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Efficient management of P in crop production requires the development of tools to quantify the P status of plants. Our objectives were to establish the relationship between P and N concentrations of spring milling wheat (Triticum aestivum L.) during the growing season and, in particular, to determine the critical P concentration required to diagnose P deficiency. Shoot biomass and P and N concentrations were determined weekly and grain yield was measured at harvest in an experiment with four to six N rates conducted over 2 yr (2004 and 2005) at three sites with adequate soil P for growth each year. Both shoot P and N concentrations decreased with time as shoot biomass increased during the growing season. They also increased with N fertilization, suggesting that they are closely related. The relationship between shoot P and N concentrations under nonlimiting N conditions is described by a linear function (P = 0.94 + 0.107N, R2 = 0.59, P < 0.001; n = 76) in which concentrations are expressed in g kg–1 dry matter (DM). Under limiting N conditions (relative grain yield <0.80), the relationship was different (P = 1.70 + 0.092N (R2 = 0.48; P < 0.001; n = 19) with greater P concentrations for a given N concentration. These relationships approximate the critical P concentration under both nonlimiting and severely limiting N conditions. This critical P concentration can then be used to quantify the degree of P deficiency during the current growing season.
Abbreviations: DM, dry matter • SEM, standard error of the means
Relationship between Phosphorus and Nitrogen Concentrations in Spring Wheat
Noura Ziadia,*,
Gilles Bélangera,
Athyna N. Cambourisa,
Nicolas Tremblayb,
Michel C. Nolina and
Annie Claessensa
a Agriculture and Agri-Food Canada (AAFC), Soils and Crops Research and Development Centre, 2560 Hochelaga Blvd., Québec, QC, Canada G1V 2J3
b AAFC, 430 Gouin Blvd., St-Jean-sur-Richelieu, QC, Canada, J3B 3E6
* Corresponding author (ziadin{at}agr.gc.ca).
Received for publication April 3, 2007.
Efficient management of P in crop production requires the development of tools to quantify the P status of plants. Our objectives were to establish the relationship between P and N concentrations of spring milling wheat (Triticum aestivum L.) during the growing season and, in particular, to determine the critical P concentration required to diagnose P deficiency. Shoot biomass and P and N concentrations were determined weekly and grain yield was measured at harvest in an experiment with four to six N rates conducted over 2 yr (2004 and 2005) at three sites with adequate soil P for growth each year. Both shoot P and N concentrations decreased with time as shoot biomass increased during the growing season. They also increased with N fertilization, suggesting that they are closely related. The relationship between shoot P and N concentrations under nonlimiting N conditions is described by a linear function (P = 0.94 + 0.107N, R2 = 0.59, P < 0.001; n = 76) in which concentrations are expressed in g kg–1 dry matter (DM). Under limiting N conditions (relative grain yield <0.80), the relationship was different (P = 1.70 + 0.092N (R2 = 0.48; P < 0.001; n = 19) with greater P concentrations for a given N concentration. These relationships approximate the critical P concentration under both nonlimiting and severely limiting N conditions. This critical P concentration can then be used to quantify the degree of P deficiency during the current growing season.
Abbreviations: DM, dry matter • SEM, standard error of the means
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INTRODUCTION
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APPLICATIONS OF P FERTILIZERS on spring wheat grown in eastern Canada are common and the rates used are principally based on soil test analyses. This soil testing, however, has not always been reliable when applied to diverse soil types and climatic conditions (Reuter et al., 1995). Plant tissue analyses could be used to complement soil test analyses by diagnosing P deficiency in growing crops (Rashid et al., 2005). Plant tissue analyses measure nutrients that have been absorbed by plants and are considered a reliable indicator of the soil nutrient fraction available to plants (Elliott et al., 1997a). The physiological basis for assessing the P status by plant analysis is that a predictable relationship exists between the concentration of a nutrient measured in whole plants or a specific part of the plant and a yield parameter (Lewis et al., 1993). Such relationships have been established between P and shoot yield in wheat plants grown in a glasshouse (Elliott et al., 1997a, 1997b) and in field conditions (Elliott et al., 1997c).
Critical nutrient concentrations separate nutrient deficiency from nutrient sufficiency but they vary with plant parts, physiological age, and environmental factors (Munson and Nelson, 1990; Westfall et al., 1990; Rashid et al., 2005). For that reason, critical nutrient ranges have been recommended to account for variance among these relationships (Dow and Roberts, 1982; Smith and Loneragan, 1997). In Australia, the critical P range for wheat has been estimated at 1.8 to 6.1 g kg–1 DM during the growing season (Bolland and Paynter, 1994; Hocking, 1994).
A diagnostic of P nutrition based on the relationship between P and N concentrations during growth was first proposed in France for perennial grasses (Salette and Huché, 1991; Duru et al., 1997). The positive relationship between P and N concentrations reflects the dilution of both elements as shoot biomass increases. For timothy (Phleum pratense L.) and corn (Zea mays L.) grown under nonlimiting P conditions, the strong relationship between P and N concentrations was used to establish the critical P concentration for shoot growth which was defined as a function of shoot N concentration and the level of N deficiency (Bélanger and Richards, 1999; Ziadi et al., 2007). We are not aware of any study of this relationship between P and N concentrations in the shoot biomass of wheat grown under varying rates of N fertilization and the use of this relationship to estimate the critical P concentration.
Our objective was to establish the relationship between P and N concentrations in spring wheat during the growing season by using data obtained under a wide range of levels of N nutrition and pedo-climatic sites known to have adequate soil P for growth. More specifically, we wanted to use this relationship to determine the critical P concentration for shoot growth, which could be used to diagnose and quantify P deficiency during the growing season.
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MATERIALS AND METHODS
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Site Description and Treatments
The relationship between P and N concentrations in spring wheat was studied using data obtained from an experiment conducted at three sites each year for 2 yr (2004 and 2005) in Quebec, Canada: Lanoraie (45°57' N, 73°19' W), Ste-Victoire (45°55' N, 73°06' W), and L'Acadie (45°17' N, 73°20' W) in 2004 and Lanoraie, St-Ours (45°54' N, 73°08' W), and L'Acadie in 2005. These sites were selected to represent different soil textures and previous crop conditions (Table 1
) within the area of spring wheat cultivation in Quebec.
Soil properties, climatic data, planting, and fertilization dates are presented in Table 1. Precipitation and temperature data were collected at the Environment Canada L'Assomption station (45°48' N, 73°25' W) for the Lanoraie site, at the Environment Canada Fleury station (45°48' N, 73°00' W) for Ste-Victoire and St-Ours sites, and at the Environment Canada L'Acadie station (45°17' N, 73°21' W) for the L'Acadie site. AC Barrie, a recommended spring milling wheat cultivar in Québec, was used at all sites. Before planting, composite soil samples were taken from each site in the surface layer (0–20 cm) to determine chemical and physical soils properties. 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). The quantity of Mehlich-3 extractable P and Al was determined according to the method of Tran and Simard (1993). The P and Al concentrations in the extracts were measured on plasma (ICP–OES, Perkins Elmer, Model 4200DV, Shelton, CT). Saturation in P was determined as the ratio of soil P to Al content as extracted by Mehlich-3. Particle size analysis was performed by the hydrometer method after oxidizing the organic matter (Sheldrick and Wang, 1993).
Treatments consisted of six N rates (0, 40, 80, 120, 160, and 200 kg N ha–1) except at L'Acadie where five N rates were used in 2004 (0, 30, 70, 110, and 150 kg N ha–1) and four in 2005 (30, 60, 90, and 120 kg N ha–1). A randomized complete block design with four replicates was used at each experimental site. At seeding, all plots received 30 kg N ha–1 as ammonium nitrate (34–0–0), except those with no N fertilization (0 kg N ha–1). At either the end of the jointing stage or the beginning of the heading stage of development as defined by Zadoks et al. (1974; Table 1), a second N application as calcium ammonium nitrate (27–0–0) was broadcast by hand to obtain the desired N rate for each plot. At planting, P and K fertilizers, as triple superphosphate and muriate of potash respectively, were applied according to soil analysis and local recommendations (CRAAQ, 2003). Thus, 15 kg P ha–1 and 10 kg K ha–1 in 2004 and 22.5 kg P ha–1 and 22.5 kg K ha–1 in 2005 were broadcast at each site. Soil available P, following P application, was then considered adequate for high crop yield at all sites (CRAAQ, 2003). Plot size was 10 by 10 m except at L'Acadie where plot size was 6 by 10 m. Seeding rate was 150 kg ha–1 and a row spacing of 0.15 m was used.
Sample Collection and Analysis
Shoot biomass was sampled weekly for 8 wk in 2004 and 5 wk in 2005 using a 0.28 by 0.72 m quadrat in each plot. We excluded data from sampling dates for which the shoot biomass was <1.0 Mg DM ha–1 (Tables 2, 3, and 4). Whole plants were cut at ground level using pruning-scissors. Shoot biomass was weighed fresh and subsamples of approximately 500 g were collected for analysis. Subsamples were dried at 55°C in a forced-draft oven for 7 d, ground to pass through 1-mm screen in a Wiley mill, and stored at room temperature before laboratory analyses. Samples of 0.1 g of dried and ground wheat were mineralized using a mixture of sulfuric and selenious acids, as described by Isaac and Johnson (1976). The P and N concentrations in plant tissue were measured on a QuikChem 8000 Lachat autoanalyzer (Zellweger Analytic Inc., Lachat Instruments Division, Milwaukee, WI) using the Lachat method 13–107–06–2-E and 15–501–3, respectively (Lachat Instruments, 2005). Grain yield was determined in each plot using a plot combine (Wintersteiger, Model NM-Elite) on a 10 m2 (6.7 by 1.5 m) area located in the middle of each plot. The grain was dried at 55°C until constant weight; grain yield was adjusted to 13.5% moisture.
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Table 2. Shoot P and N concentrations during the growing season, grain yield, and relative grain yield of spring wheat at Lanoraie in 2004 and 2005.
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Table 3. Shoot P and N concentrations during the growing season, grain yield and relative grain yield of spring wheat at Ste-Victoire in 2004 and St-Ours in 2005.
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Table 4. Shoot P and N concentrations during the growing season, grain yield and relative grain yield of spring wheat at L'Acadie in 2004 and 2005.
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Data Analysis
Data for each sampling date at each site were subjected to an analysis of variance using the PROC GLM (SAS Institute, 2001) and standard errors of the means (SEM) were calculated. The relationship between P and N concentrations under nonlimiting and limiting N conditions was described by linear regressions (SAS Institute, 2001). The relative grain yield was used to distinguish nonlimiting and limiting N conditions; it was calculated as the grain yield of each treatment divided by the maximum grain yield at each site.
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RESULTS AND DISCUSSION
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Grain Yield and N and P Concentrations during the Growing Season
Nitrogen fertilization significantly increased grain yield at four of the six site-years (Tables 2, 3, and 4); N fertilization did not affect grain yield at St-Ours and L'Acadie in 2005. At sites where a significant difference was observed, grain yield ranged from 1.2 to 2.0 Mg ha–1 where no N fertilization was applied (0 kg N ha–1) and from 1.7 to 2.8 Mg ha–1 where N was applied; this is a typical range for spring wheat grown in this area (Statistique Québec, 2002). The increase in grain yield with fertilizer N application is consistent with other studies conducted in eastern Canada (Bélanger et al., 1998; Nass et al., 2002) and with AC Barrie grown in western Canada (Selles et al., 2006). The relative grain yield with no N applied ranged from 0.45 to 1.0, indicating a wide range of levels of N nutrition among sites. In Atlantic Canada, Bélanger et al. (1998) reported a range of 0.33 to 0.76 for the relative yield of spring wheat grown without N fertilization at six sites.
Increasing N fertilization increased shoot N concentration on most sampling dates (Tables 2, 3, and 4). This positive effect of N fertilization on N concentration has been reported in many species including wheat (Justes et al., 1994; Elliott et al., 1997b; Ishaq et al., 2001). Nitrogen fertilization, however, inconsistently affected P concentration (Tables 2, 3, and 4). Elliott et al. (1997b), in Australia, reported that P concentrations in wheat shoots usually declined as N fertilization increased whereas Ishaq et al. (2001) in a study on wheat cultivated in Pakistan reported no effect of increasing N fertilization on P concentration. In studies on corn (Ziadi et al., 2007) and timothy (Bélanger and Richards, 1999) conducted in eastern Canada, however, an increase in P concentration with increasing N fertilization was observed.
Decrease in Phosphorus and Nitrogen Concentrations with Time
Phosphorus and N concentrations in the shoot biomass generally decreased with time (Tables 2, 3, and 4). At the Lanoraie site in 2005, however, there was a transient increase in N concentration with time, primarily on the second sampling date following the second N application (Table 2
). The decrease in N concentration with time or advancing maturity has been reported for potato (Solanum tuberosum L.) (Bélanger et al., 2001), timothy (Bélanger and Richards, 1997; 1999), corn (Plénet and Lemaire, 2000; Ziadi et al., 2007), and wheat (Hocking, 1994; Justes et al., 1994). Nitrogen concentrations varied from a maximum of 36.3 g kg–1 DM at L'Acadie on 9 July 2004 to a minimum of 6.0 g kg–1 DM observed at Ste-Victoire on 26 July 2004 (Tables 2, 3
, and 4
). Higher values of N concentration were reported by Justes et al. (1994) for wheat grown with different N fertilization rates in France (15–53 g N kg–1 DM) and by Hocking (1994) on irrigated spring wheat in Australia (17–41 g N kg–1 DM). These differences in N concentrations between studies could be due in part to differences in maturity at sampling. We sampled from stage 31 (stem elongation) to stage 69 (end of flowering) whereas Justes et al. (1994) sampled from approximately stage 26 (tillering) to stage 60 (beginning of flowering) and Hocking (1994) sampled from stage 21 (tillering) to stage 65 according to the Zadoks scale (Zadoks et al., 1974). Differences in N concentration among studies could also be associated with the cultivars used.
A decrease in P concentration with time has also been reported in wheat (Bolland and Paynter, 1994; Hocking, 1994; Elliott et al., 1997a) and other species (Bélanger and Richards, 1999; Ziadi et al., 2007). Phosphorus concentrations varied from a maximum of 5.2 g kg–1 DM at L'Acadie on 9 July 2004 to a minimum of 1.3 g kg–1 DM observed at Ste-Victoire on 26 July 2004 (Tables 2, 3, and 4). Similar ranges of P concentration were reported on Australian wheat (1.8–6.1 g kg–1 DM, Bolland and Paynter, 1994; 2.8–5.2 g kg–1 DM, Hocking, 1994).
Decrease in Phosphorus Concentration with Shoot Biomass
Shoot P concentration decreased as shoot biomass increased across all six sites (Fig. 1
). For a given shoot biomass, P concentration tended to decrease with decreasing N rates, particularly at Lanoraie and L'Acadie in 2004 (Fig. 1). Similar results were reported in timothy (Bélanger and Richards, 1999) and corn (Ziadi et al., 2007), which indicates a direct positive effect of N fertilization on P concentration. On the last sampling dates, wheat grown under all N rates tended to have similar shoot biomass P concentrations (Fig. 1). This result was also reported in timothy (Bélanger and Richards, 1999) and corn (Ziadi et al., 2007), and has been attributed to a dilution effect. High N fertilization rates increase shoot biomass and thus increased P dilution, resulting in a P concentration similar to that obtained under limiting N conditions.
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Fig. 1. Shoot phosphorus concentration (P) as a function of shoot biomass of spring wheat fertilized with various N rates in an experiment conducted at three sites in each of 2 yr (2004 and 2005).
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Relationship between Phosphorus and Nitrogen Concentrations
The shoot P concentration increased with increasing N concentration at all sites (Fig. 2
), except at Lanoraie in 2005; this effect at Lanoraie can be explained by the transient increase in N concentration with time while P concentration decreased (Table 2). Increased P concentration is therefore associated with increasing N concentration in wheat. For a given N concentration, however, the P concentration generally decreased with increasing N fertilization rates (Fig. 2). This relationship has also been observed in grasses (Salette, 1990), permanent pastures (Duru and Ducrocq, 1997), timothy (Bélanger and Richards, 1999), and recently in corn (Ziadi et al., 2007).
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Fig. 2. Shoot phosphorus concentration (P) as a function of nitrogen concentration (N) of spring wheat fertilized with various N rates in an experiment conducted at three sites in each of 2 yr (2004 and 2005).
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The relationship between P and N concentrations is reported differently for limiting and nonlimiting N conditions (Duru and Ducrocq, 1997; Bélanger and Richards, 1999; Ziadi et al., 2007). To determine these two contrasting N conditions, we used relative yield. Values of relative yield of 1.00 indicate that the N fertilization treatment resulted in maximum grain yield and thus the crop was in a situation of nonlimiting N supply. Values of relative yield <1.00 indicates a N deficiency. However, N fertilization treatments with a relative yield 
0.90 were often not significantly different for their grain yield than those with a relative yield of 1.00 (Tables 2, 3, and 4). Therefore, we considered that N was not limiting wheat grain yield when the relative yield was 0.90. Based on this assumption, we selected N fertilization treatments with relative yield 0.90 to determine the relationship between P and N concentrations under nonlimiting N conditions. For limiting N conditions, we used treatments with a relative grain yield <0.80 for which grain yield was significantly different from N fertilization treatments used in the nonlimiting N condition relationship (Tables 2, 3, and 4).
Critical Phosphorus Concentration under Nonlimiting Nitrogen Conditions
The relationship between P and N concentrations under nonlimiting N conditions can be described by the following linear function:
 | [1] |
in which both concentrations are expressed in g kg–1 DM (Fig. 3
). This relationship approximates the critical P concentration under nonlimiting N conditions that is, the minimum P concentration needed to achieve maximum shoot growth. It assumes that soil P availability did not limit shoot growth. Under the nonlimiting N conditions of our study, P concentrations ranged from 1.4 to 5.2 g kg–1 DM (Fig. 3), a range similar to that reported by Elliott et al. (1997a) (1.6–7.1 g kg–1 DM) for wheat grown under nonlimiting P conditions in Australia. Linear relationships between P and N concentrations were also reported for timothy (P = 1.46 + 0.069N with P and N in g kg–1 DM; R2 = 0.79, P < 0.001) (Bélanger and Richards, 1999) and corn (P = 1.00 + 0.094N with P and N in g kg–1 DM; R2 = 0.76, P < 0.001) (Ziadi et al., 2007) grown in eastern Canada. The intercept and the slope of the relationship between P and N concentrations observed in our study on wheat were closer to those reported for corn (Ziadi et al., 2007) than those reported for timothy (Bélanger and Richards, 1999) (Fig. 3). Further research is required to validate these equations under a broader range of environments and species.
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Fig. 3. Shoot phosphorus concentration (P) as a function of nitrogen concentration (N) of spring wheat in an experiment conducted at three sites in each of 2 yr (2004 and 2005) under nonlimiting N conditions (relative grain yield >– 0.90). Solid line, linear regression [P = 0.94 + 0.107N, R2 = 0.59, P < 0.001, n = 76].
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Critical Phosphorus Concentration under Limiting Nitrogen Conditions
Under limiting N conditions, the relationship between P and N concentrations can be described by the following linear function:
 | [2] |
For a given N concentration, the P concentration was higher under limiting N conditions than under nonlimiting N conditions at Lanoraie in 2004 and 2005, (Fig. 4
). A similar observation was reported by Duru (1992) on permanent pastures, Bélanger and Richards (1999) on timothy, and Ziadi et al. (2007) on corn. However, at Ste-Victoire and L'Acadie in 2004, the relationship between P and N concentrations was generally similar under limiting and nonlimiting N conditions (Fig. 4). With no N applied, the level of N deficiency indicated by the relative grain yield was greater at Lanoraie in 2004 (0.45) and 2005 (0.51) than at Ste-Victoire (0.72) and L'Acadie (0.61) in 2004 (Tables 2, 3, and 4). This suggests that the adjustment of P to N concentrations is relatively good when the level of N nutrition is close to the optimal, that is, with a relative yield near or >0.80. This adjustment, however, is not as good under conditions of relatively severe N deficiencies.
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Fig. 4. Shoot phoshporus concentration (P) as a function of nitrogen concentration (N) of spring wheat in an experiment conducted at three sites in 2004 and one site in 2005 under limiting N conditions (relative grain yield <0.80); the other two sites in 2005 had relative grain yield >0.80. Solid line, linear regression (P = 0.94 + 0.107N) for nonlimiting N conditions as presented in Fig. 3; dashed line, linear regression [P = 1.70 + 0.092N, R2 = 0.48, P < 0.001, n = 19] for limiting N conditions.
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Implications for P Diagnostic in Spring Wheat
Our results show that P and N concentrations decrease during growth, and that critical P concentration is a function of the N concentration and the level of N deficiency. Producers applying adequate rates of N to optimize wheat yield could assume a negligible effect of N deficiency on the relationship between P and N concentrations and use the relationship proposed for nonlimiting N conditions. In situations of severe N deficiency, however, a different relationship should be used. These relationships thus provide a tool to estimate the critical P concentration, which is essential to assess the P status of spring wheat during the growing season. An index of P nutrition could be calculated by dividing the P concentration in a given situation by the critical P concentration predicted by Eq. [1] and [2]. Combined with an index of N nutrition (Bélanger et al., 2001), it provides the tools required to diagnose N and P deficiencies and imbalances in spring wheat. This plant-based analysis could also complement soil analyses in determining fertilization for spring wheat. Since early P deficiency cannot be easily alleviated with later applications, producers can use this tool to adjust P fertilization in the following growing season (Grant et al., 2001).
Several authors have suggested that critical P ranges should be used because critical nutrient concentration varies with plant parts, physiological age, and with environmental factors (Munson and Nelson, 1990; Westfall et al., 1990; Rashid et al., 2005). The relationship between P and N concentrations that we are proposing to determine the critical P concentration alleviates this problem of variability due to physiological age and environmental factors and, therefore, diminishes the need to use critical P ranges. However, further research is needed to determine how effective this approach of characterizing the critical P concentration would be in differentiating situations of P deficiency and P sufficiency of spring wheat grown under contrasted conditions of P supply.
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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.
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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.
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INTRODUCTION
