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Published in Agron. J. 97:211-218 (2005).
© American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA

Production Papers

Seed Priming Does Not Improve Corn Yield in a Humid Temperate Environment

K. D. Subedi* and B. L. Ma

Eastern Cereal and Oilseed Res. Cent. (ECORC), Cent. Exp. Farm, Res. Branch, Agric. and Agri-Food Canada, 960 Carling Ave., Ottawa, ON, Canada, K1A 0C6

* Corresponding author (subedik{at}agr.gc.ca)

Received for publication May 10, 2004.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Early emergence and stand establishment of corn (Zea mays L.) is considered to be one of the most important yield-contributing factors in eastern Ontario. A pot experiment and two field experiments were conducted in Ottawa, Canada, to evaluate the effects of seed priming with water, osmotic solution (2.5% KCl), and plant growth regulators (indole acetic acid, cytokinin, ethephon and gibberellic acid) on emergence, seedling vigor, N response, and grain yield of corn. Time to seedling emergence, seedling vigor, and growth were measured in a pot experiment under a greenhouse condition while field performances, N response, and grain yield were determined in field experiments. In the greenhouse study, none of the treatments were better than the unsoaked control. Under field conditions, both hybrids and N application had significant effects on grain yield, but there was no yield advantage due to any of the seed treatments. Seed soaking with 20 ppm gibberallic acid (GA3) solution for 30 min improved seedling vigor (i.e., seedling height and growth), but this was not translated into greater grain yield. Seed soaking with water for 16 h significantly reduced percentage emergence and final plant stand in 2002 while in 2003, seed soaking with 2.5% KCl and 20 ppm GA3 solution for 16 h significantly reduced plant stand and grain yield under the 150 kg N ha–1 treatment. Despite some positive effects of seed priming on seedling vigor and stand establishment, none of the seed-priming treatments tested showed beneficial effects on grain yield and N efficiency under the temperate-humid conditions such as in eastern Ontario.

Abbreviations: CCC, chlormequat chloride • GA3, gibberallic acid • IAA, indol acetic acid • NDVI, normalized difference vegetation index • PGR, plant growth regulator


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
COOL SOIL TEMPERATURES in late spring leading to poor crop establishment and short growing season coupled with periods of drought are the major production limitations of corn in eastern Ontario. The growing season is limited by cool temperatures at both ends: Cool soil temperatures at planting reduce the germination and early vigor while killing frost during later part of the grain filling limits yield potential. Technology that enhances early emergence and stand establishment would enable the crop to capture more soil moisture, nutrients, and solar radiation and mature before a killing frost. Rapid and uniform field emergence is an essential prerequisite to reach the yield potential, quality, and ultimately profit in annual crops (Parera and Cantliffe, 1994).

Heydecker et al. (1973) defined seed priming as a presowing treatment in osmotic solution that allows seeds to imbibe water to proceed to the first stage of germination but prevents radicle protrusion through the seed coat. But, recently Taylor et al. (1998) used a broader term, "seed enhancement," which includes presoaking hydration (priming), coating technologies, and seed conditioning. Therefore, seed priming can be accomplished through different methods such as hydro-priming (soaking in water), osmo-priming (soaking in osmotic solutions such as polyethylene glycol, potassium salts, e.g., KCl, K2SO4), solid matrix priming, and using plant growth regulators (PGRs) (Dearman et al., 1987; Kulkarni and Eshanna, 1988; Paul and Choudhury, 1991; Harris et al., 1999; Capron et al., 2000; Chiu et al., 2002). It is seen as a viable technology to enhance rapid and uniform emergence, high vigor, and better yields mostly in vegetable and flower species (Dearman et al., 1987; Parera and Cantliffe, 1994; Bruggink et al., 1999) and some field crops (Basra et al., 1988; Hartz and Caprile, 1995; Harris et al., 1999; Chiu et al., 2002; Giri and Schillinger, 2003; Murungu et al., 2004). Seed priming has been a common seed treatment to reduce the time between seed sowing and seedling emergence and the synchronization of emergence (Parera and Cantliffe, 1994).

Different PGRs have been used to alter growth, physiological process, enzyme activities, nutrient uptake, and resistance to environmental stresses in plants. Through physiological action, they accelerate or retard rate of growth and initiation of reproductive organs and stimulate the size of plant structures. The most commonly used PGRs in field crops are chlormequat chloride (CCC; 2-chloroethyl-trimethyl-ammonium chloride), ethephon (2-chloroethyl phosphonic acid), GA3, cytokinin (kinetin), and indole-3 acetic acid (IAA). There are some reports that foliar application of different PGRs improved crop performance. Koranteng and Matthews (1982) found that use of 20 µg mL–1 GA3 at early Growth Stage 13 (Zadoks et al., 1974) significantly increased tillering, number of ears per plant, and grain yield in barley (Hordeum vulgare L.). Ma and Smith (1992) also found similar effects of CCC and ethephon when applied at Growth Stage 13. The use of ethephon improved N uptake in grains of wheat (Triticum aestivum L.) and barley (Pietola et al., 1999) and increased grain protein concentration in barley (Bulman and Smith, 1993). Application of ethephon and CCC reduced main culm height up to 20%, in barley and wheat, and tiller production was enhanced by ethephon (Rajala and Peltonen-Sainio, 2001). Poljakoff-Mayber et al. (2002) observed that GA3 was involved in the germination process of oat (Avena sativa L.) seeds. Oat plants treated with PGR had up to five more green leaves per culm at anthesis (Peltonen-Sainio et al., 2003).

There are some studies on the effect of seed priming with PGR on germination and growth rate of corn. Basra et al. (1989) found that priming of corn seed using polythelene glycol or potassium salts (K2HPO4 or KNO3) resulted in accelerated germination at a chilling germinator (10°C). Similarly, Basra et al. (1989) reported a marked improvement in germination when the pretreated corn seeds with substituted phthalimide, GA3, and abscisic acid (ABA) were germinated under sub-and supraoptimal temperature regimes.

Field experiments conducted in semiarid environments revealed that seed soaking overnight with tap water resulted in early emergence, deeper roots, early flowering and maturity, and higher yield in upland rice (Oryza sativa L.), chickpea (Cicer arietinum L.), and corn (Harris et al., 1999). Singh and Agrawal (1977) reported that in wheat, seed soaking in tap water overnight increased N uptake up to 11 kg ha–1. There are some reports showing similar benefits of other chemicals and PGR for seed priming. Misra and Dwivedi (1980) found that seed soaking in 2.5% potassium chloride (KCl) solution for 12 h before sowing increased yield of wheat by 15%. Paul and Choudhury (1991) observed that seed soaking with 0.5 to 1% solutions of KCl or potassium sulfate (K2SO4) significantly increased plant height, yield attributes, and grain yield in wheat. In field-grown corn, Kulkarni and Eshanna (1988) found that presowing seed treatment with IAA at 10 ppm improved root length, rate of germination, and seedling vigor, especially for seeds from poor-quality seed lots. Hartz and Caprile (1995) used the solid matrix priming in sweet corn and found that there was an enhanced emergence in a cold-stressed condition, but results were inconsistent under field conditions. Similarly, Chiu et al. (2002) observed hastened germination in sweet corn when primed using polyethylene glycol. Nevertheless, some reports showed no or limited benefits of seed priming. For example, Giri and Schillinger (2003) noted that none of the seed-priming media used (i.e., water, KCl, and polyethylene glycol) improved field emergence and subsequent grain yield in deep-planted winter wheat. Similarly, Murungu et al. (2004) in a semiarid environment of Zimbabwe found little or no effect of seed priming on corn. The success of seed priming is influenced by the complex interaction of factors including plant species, water potential of the priming agent, duration of priming, temperature, seed vigor and dehydration, and storage conditions of the primed seed (Parera and Cantliffe, 1994).

It was hypothesized that under the cool soil temperature and growing-season-limited conditions, seed priming with PGR or osmotic solutions before planting would lead to earlier emergence and more uniform stand establishment, thereby enhancing N uptake, early maturity, and higher yield of corn. The objective of this study was to assess seed-priming effects on seedling emergence, early growth, N efficiency, and grain yield of corn in eastern Ontario.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Greenhouse Experiment
To assess the priming effects on seedling emergence, early vigor, and growth rate, response of corn seeds soaked in water, osmotic solution, and different PGRs were studied in a controlled greenhouse. Two corn hybrids (‘N17-C5 Bt’ and ‘Pioneer 38W36 Bt’) were treated with the following seed-soaking solutions: (i) unsoaked seed (control), (ii) tap water, (iii) 2.5% KCl, (iv) 20 ppm IAA, (v) 100 ppm Soil TRIGGRR (cytokinin), (vi) 1000 ppm ethephon (ethrel), and (vii) 20 ppm GA3. The duration of soaking was for 16 h (Harris et al., 1999). Three additional treatments [(viii) 20 ppm GA3, (ix) 100 ppm ethephon, and (x) 1000 ppm cytokinin], which were soaked only for 30 min, were also included, making a total of 10 treatments. All concentrations were prepared based on active ingredients (a.i.), except for KCl and cytokinin, which were product based. The concentrations used for each treatment are either based on other studies or as prescribed by the suppliers. For Treatments 1 to 7, 100 g (>340 seeds) of each hybrid was soaked in 200-mL solutions for 16 h in plastic containers. After soaking, seeds were drained in a tray, and their weights were recorded immediately (Table 1). For the Treatments 8 to 10, seeds were soaked for 30 min to determine if there were no differences between brief soaking and overnight (16 h) soaking. The soaked seeds were then allowed to air-dry in room temperature (23°C) for 24 h. After air drying, the weights of the seeds were recorded again, and total amount of moisture absorbed during soaking was derived (Table 1). Germination test of the dried seeds was performed in which three lots of 100 seeds (i.e., three replications) for each treatment were rolled in individual moist paper towels and kept at room temperature for 72 h. After 72 h, total germinated seeds (i.e., seeds having >5-mm radicle and coleoptiles) were counted in all 300 seeds, and the lengths of radicle and coleoptile were measured in 10 randomly selected seeds from each of the three lots.


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  		Table 1. Changes in weight and moisture content of corn seed after soaking for 16 h and air drying for 24 h in room temperature (23°C). The initial seed weight taken was 100 g for each treatment and soaked in 200 mL of different solutions. The seed-soaking treatment solutions are T1, unsoaked control; T2, tap water for 16 h; T3, 2.5% KCl for 16 h; T4, 20 ppm indol acetic acid (IAA) for 16 h; T5, 20 ppm gibberallic acid (GA3) for 16 h; T6, 100 ppm ethephon for 16 h; T7, 1000 ppm cytokinin for 16 h; T8, 20 ppm GA3 for 30 min.; T9, 100 ppm ethephon for 30 min; and T10, 1000 ppm cytokinin for 30 min.

 
Plants were grown in 3-L plastic pots (10 cm diam.) filled with a mixture of soil, peat moss, vermiculite, and perlite (3:1.5:1:1 v/v). The pots were arranged in a completely randomized design with three replications inside a greenhouse. Three uniform seeds were planted at 5-cm depth per pot on 14 Mar. 2003. Daily observations were made to record the time taken to seedling emergence and appearance of each ligule. Time to seedling emergence was recorded when coleoptiles above the soil surface were fully visible. At seedling emergence (5 d after planting), height of each seedling was measured, and 1 g of commercial fertilizer 20:20:20 (N:P2O5:K2O) was applied per pot. At the three-leaf stage, the pots were thinned to one plant per pot. After thinning, 300 mL of Hoagland solution (100 mg N g–1) was applied in each pot. Pots were regularly watered thereafter. The temperature inside the greenhouse was maintained at 25/15°C (day/night regime ± 1°C) with 16-h photoperiod. At 32 d after planting, when plants were at V7 (Ritchie et al., 1993), leaf chlorophyll content was measured using a SPAD meter (SPAD–502 Chlorophyll Meter, Minolta Camera Co. Ltd., Tokyo, Japan) on the uppermost fully expanded leaf (i.e., the seventh leaf), and then plants were cut at crown level. Length of the plant from the crown to the tip of the longest extended leaf was measured. Leaves were separated from the stem and total number of leaves; number of visible internodes and length of stem were measured. Roots were separated from the growing medium and washed with tap water. All plant parts were oven-dried at 80°C for >72 h, and their dry weights were recorded.

Field Experiments
Two field experiments were conducted in 2002 and 2003, in Ottawa, Canada (45°22' N, 75°43' W), in well-drained, unirrigated fields with 25-cm-deep dark gray brown silt loam soil (Eutrochepts). The soil contained 5.8 µg NO3–N g–1, 8 µg Bray P g–1, and 85 µg test K g–1 and had a pH of 6.6 in water in 2002 and contained 6.58 µg NO3–N g–1, 21 µg Bray P g–1, and 266 µg test K g–1 and had a pH 6.5 in water in 2003. The experiments were laid out in a split-split plot design with four replications in both years. Nitrogen (0 and 150 kg ha–1) was the main plot, hybrid in subplots, and seed treatment in sub-subplots. Three pairs of Bt (Bacillus thuringiensis) and non-Bt hybrids representing early (N17-C5 Bt and ‘N15-B4’), medium (Pioneer 38W36 Bt and ‘Pioneer 3893’), and full-season (‘DKC 42-22Bt’ and ‘DK 427’) maturity groups for the region were grown in 2002 while only one each from early (N17-C5 Bt) and midseason (Pioneer 38W36 Bt) were used in 2003 because there were no hybrid x seed treatment or hybrid x N interactions in 2002. The seeds were supplied from the same sources in both years. In 2002, seeds were soaked for 16 h in tap water or not soaked. In 2003, there were five additional treatments, making a total of seven treatments as tested in the greenhouse study [(i) unsoaked (control) and seed soaking with (ii) tap water, (iii) 2.5% KCl solution, (iv) 20 ppm IAA solution, (v) 1000 ppm cytokinin solution, (vi) 100 ppm ethephon solution, and (vii) 20 ppm GA3 solution]. For seed treatment, solutions of different salts and PGR were prepared in tap water as per the concentrations required for different treatments. Corn seeds (1.3 kg) were soaked in 2-L solutions for 16 h (Harris et al., 1999, 2002). In 2002, soaked seeds were drained and air-dried for 3 h before planting. While in 2003, soaked seeds were air-dried in room temperature for 24 h when their original moisture content was achieved (based on the greenhouse study, Table 1). Planting was done on 27 May in 2002 and on 15 May in 2003 to achieve a plant population density of 75000 plants ha–1.

In both years, each experimental plot contained four 10-m rows of corn spaced 76 cm apart. Fertilizer P and K were applied preplanting according the soil test recommendations. In treatment with 150 kg N ha–1, fertilizer NH4NO3 (33.5% N) was applied just before corn planting. Herbicides Dual II Magnum (S-metolachlor {2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(1S)-2-methoxy-1-methylethyl]acetamide}/benoxacor [4-(dichloroacetyl)-3,4-dihydro-3-methyl-2H-1,4-benzoxazine]) + Field Star (flumetsulam {N-(2,6-difluorophenyl)-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonamide}) at 1.75 L ha–1 were applied preplanting to control weeds in both years. Manual weeding was done to remove any weeds escaped from the herbicides.

Measurements
Daily weather data (rainfall and air temperatures) at the experimental site were recorded in both years. Time taken to complete emergence, V8, 50% silking, and physiological maturity were recorded. At the three-leaf stage, the number of plants emerged in the middle two rows were counted. Leaf chlorophyll content was measured at V6, V8, V10, V12, silking, and 2 wk after silking using SPAD-502 in five random plants from the middle two rows. Canopy reflectance was also measured at V6 and silk stage in 2002 and only at silking in 2003 using a hand-held multispectral radiometer (MSR-16, Crop Scan Inc., Rochester, MN), and the reflectance values were expressed as the normalized difference vegetation index (NDVI). At V6 stage, five random plants from Row 4 were harvested to measure their dry weights. At maturity, the number of plants were counted in Rows 2 and 3. Five plants from Row 4 were harvested for the determination of harvest index. Rows 2 and 3 were combine-harvested for the grain yield. Samples were oven-dried at 80°C until constant weight. Grain yields were corrected to 155 g kg–1 moisture.

The experimental data for each year were subjected to the analysis of variance using a general linear model (SAS Inst., 1990). Treatment mean differences were separated by the Duncan's multiple range test (DMRT0.05) if the F tests were significant (P ≤ 0.05).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
In both years, the air temperature remained >10°C, and there was excess soil moisture during the emergence and seedling establishment period (Fig. 1). Wet and cool growing conditions occurred in 2002 during the emergence and seedling establishment stage because of the continuous rain after planting, which resulted in reduced plant emergence (about 75% of 75000 seeds ha–1 planted in 2002 emerged compared with 91% in 2003). There was a period of brief drought bracketing the silking and early grain-filling period in 2002. In 2003, the whole growing season received evenly distributed precipitation, and crop did not experience moisture stress. In both years, there was sufficient crop heat units accumulated for crop maturity.



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  		Fig. 1. Total precipitation (mm) and mean air temperatures (°C) at the experimental site in Ottawa in 10-d intervals during the growing season of 2002 and 2003.

 
Seed Soaking and Germination
All seeds soaked for 16 h absorbed water about 40% of their initial weight while Pioneer 38W36 Bt hybrid had absorbed slightly more water than N17-C5 Bt although the difference was not significant (Table 1). Seeds soaked just for 30 min also absorbed about 13 to 15% water of their original weight. Drying of the soaked seeds in room temperature for 24 h brought the seeds back to their original moisture content in both hybrids. The germination of the soaked seeds was not different between the hybrids and soaking treatments, which ranged between 96 to 100%.

Seedling Vigor and Plant Stand
The pot experiment examined various parameters of seedling growth and development from seed imbibition to V7 stage. There were no hybrid x treatment interactions for any of the parameters measured. The two hybrids differed significantly for the length of radicle, coleoptiles, and seedling heights at emergence (5 d after planting) and at V7. In all cases, Pioneer 38W36 had greater values than N17-C5 (Table 2). Despite the taller plants of Pioneer 38W36, there was no difference between the two hybrids in the dry weights of leaves, stem, and whole plant at V7.


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  		Table 2. Morphological and phenological parameters of two corn hybrids grown in a controlled greenhouse condition until V7, averaged over 10 different priming treatments.

 
The seed-soaking treatments had no effect on time to emergence of coleoptiles, number of visible internodes and leaves, and leaf dry weight at V7. However, there were significant effects on several other parameters (Table 3). The differences due to seed treatment were mainly among some of the soaked treatments, but they were not consistently different from the unsoaked control treatment. Seed soaking with 20 ppm GA3 for 16 h significantly reduced the lengths of radicle and coleoptiles, leaf chlorophyll, stem dry weight, and whole-plant dry weight at V7. The opposite was the case when the duration of soaking was only for 30 min; these parameters were significantly greater than or similar to most other treatments (Table 3). Seed soaking with 2.5% KCl also significantly reduced the lengths of radicle and coleoptile, seedling height at emergence, and stem length at V7 compared with other treatments. On the other hand, soaking seeds with cytokinin and IAA for 16 h increased plant height and stem length compared with soaking with water. Generally, the performance of water soaking was poor for most of the parameters. It is evident from the pot experiment that although there were significant treatment differences, none of the treatments produced sustained superior effect in terms of seedling vigor and growth compared with unsoaked control treatment (Table 3).


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  		Table 3. Effect of seed priming with tap water, osmo-solutions, and various growth regulators on different parameters measured in greenhouse-grown corn averaged over two hybrids.

 
In the field experiments, soaking seeds with water significantly reduced the number of plants both at emergence and final harvest in 2002 (Table 4). This was presumably due to continuous heavy rain following corn planting (Fig. 1), causing wet soil and crusting or soil compaction. In 2003, seed soaking with 2.5% KCl significantly reduced seedling emergence and final plant stand by 5%, which concurred with the results of the pot experiment. On the other hand, seeds soaked with 100 ppm ethephon and tap water had significantly higher numbers of plants compared with soaking with 2.5% KCl and 20 ppm GA3 for 16 h (Table 4). This also agrees with the pot experiment in greenhouse that these treatments had poorly developed radicles and coleoptiles at emergence (Table 3). The results of 2003 field experiments contrast with the 2002 results where seed soaked in water had significantly reduced plant stands. The difference in the two years was that in 2002, seeds were planted after air drying for 3 h while in 2003, they were air-dried for 24 h. This indicates that if wet seeds were planted in a moist soil, germination and emergence were reduced more dramatically.


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  		Table 4. Effect of seed soaking with different treatments on the number of plants per hectare at emergence and at harvest averaged over two N rates and six corn hybrids in 2002 and two corn hybrids in 2003 grown at Ottawa.

 
There was no difference in the number of days to seedling emergence, silking, and physiological maturity in the field in both years (data not shown). Since the air temperatures at planting were >10°C in both years, the crop did not experience early cold stress as anticipated. Therefore, the responses of seed-priming treatments to cold stress were not evident as reported by Basra et al. (1988), Hartz and Caprile (1995), and Chiu et al. (2002). Plants developed normally in both years. Plant dry weight measured at V6 in both years showed no effect of seed treatment. A marginal difference in plant dry weight was observed between the hybrids in 2003: Pioneer 38W36 had higher dry weight (11.8 g plant–1) than N17-C5 (10.6 g). A substantial difference in plant dry weight at V6 was recorded due to N treatments averaged across hybrid and seed treatments (13.8 g for 150 kg N ha–1 vs. 8.8 g for 0 kg N ha–1), but there was no N x seed treatment interaction. This indicated that none of the seed treatments influenced crop phenology, early growth, and N response in the field.

Grain Yield
In 2002, although seed soaking reduced plant stand at harvest by 5.7%, there was no yield difference between the two soaking treatments. Hybrids differed in their yield potentials; generally, the longer the crop duration, the higher was the grain yield (Fig. 2). Moreover, there was no differential hybrid response to N and seed treatment or N x hybrid interaction.



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  		Fig. 2. Effect of N treatment on the grain yield of six corn hybrids in 2002 averaged over two seed-priming treatments. The vertical bars are LSD0.05.

 
In 2003, Pioneer 38W36 outyielded N17-C5 (9.5 vs. 8.4 t ha–1), but N and seed treatments did not influence the grain yields of these hybrids. When the yield data were analyzed separately for 0 and 150 kg N ha–1, seed treatment differed for grain yield at 150 kg N ha–1; however N x seed treatment interactions were not significant (P > 0.05). Seed soaking with 2.5% KCl reduced grain yield significantly compared with other treatments except for the unsoaked control and seeds soaking in cytokinin for 16 h, which were similar (Fig. 3). The lower yield in the KCl treatment might be associated with the significant reduction in plant stand. The results of the pot (Table 3) and field experiments (Fig. 3) agreed to some extent that KCl reduced plant growth, stand, and yield. Some of the treatments such as cytokinin and IAA improved seedling vigor and plant stand, but the effect was not reflected in final grain yield. It appeared that small differences at seedling stages were eliminated at crop maturity; thus yield differences were nonsignificant. It can be argued that the growing environments later in the development might have played more important roles for grain yield.



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  		Fig. 3. Effect of seed priming with different treatments for 16 h on the grain yield of corn grown with 150 kg N ha–1, averaged over two corn hybrids. The bars following with the same letter are not significant at p ≤ 0.05. IAA, indol acetic acid; GA3, gibberallic acid.

 
Synchronization and rapid seedling emergence are the commonly reported benefits of seed priming in corn (Harris et al., 1999; Murungu et al., 2004). Our hypothesis that early emergence and vigor enable plants to take up more N and utilize resources more efficiently has not been supported by these results. Similarly, the advantages of seed priming as reported by many workers in the arid and semiarid environments (e.g., Kulkarni and Eshanna, 1988; Paul and Choudhury, 1991; Harris et al., 1999) were not demonstrated, possibly because of the more humid growing environment in eastern Ontario. In both years, wet conditions were encountered immediately after planting (Fig. 1), which might have reduced the effect of seed priming, if any, on emergence and early vigor. Nevertheless, the pot experiment under controlled conditions (greenhouse) detected no superiority in seedling vigor and rate of seedling growth compared with the unsoaked control, indicating that the priming effects would not have been apparent even if the soil moisture was normal.

Response to Nitrogen
The response of crop growth to N was measured in terms of leaf chlorophyll content, canopy reflectance and grain yield. None of the seed treatments influenced N response as there was no N x seed treatment interactions for SPAD reading, NDVI, and grain yield. Nitrogen treatment has a significant effect on grain yield in both years, but the yield differences between the 0 and 150 kg N ha–1 were very small (Fig. 4), which could be attributed to lower efficiency of the preplanting applied N, sink limitation of hybrids, or releasing of more soil NO3–N at the critical time. The plants in plots treated with 150 kg N ha–1 were green with luxurious growth, but their harvest index values were smaller in both years (0.53 in 2002 and 0.51 in 2003) than in the zero N treatment (0.56 in 2002 and 0.55 in 2003), indicating that large amount of biomass was produced but its partitioning to the grain was limited.



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  		Fig. 4. Effect of N treatments on the grain yield of corn in 2002 and 2003 averaged over corn hybrids and seed treatments. The vertical bars are LSD0.05.

 
The SPAD readings were different between the N treatments in both years. The pattern of SPAD readings between the two N rates from V6 to silking in 2003 is shown in Fig. 5. A similar trend was observed in 2002, but the values were slightly lower (data not shown). Looking at the SPAD readings (Fig. 5), there seems to be more soil NO3–N available around silking stage. The SPAD values with 0 kg of N also increased to around 50, which is considered to be a status of moderate N supply. This could be one of the reasons why there was a small yield gap between 0 and 150 kg N ha–1. The canopy greenness expressed as NDVI also differed only between the two N treatments, and effects of seed treatments were not detected. Irrespective of N treatment, plants treated with ethephon had consistently lower SPAD readings for all stages measured (data not shown), possibly because of significantly higher plant stand (Table 4). The hypothesis that seed priming improves response to N has not been supported by these observations.



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  		Fig. 5. Leaf chlorophyll content measured at different stages with SPAD in the corn grown with or without 150 kg N ha–1 in 2003. The error bars are the LSD0.05.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Although some of our results showed significant improvement in early growth and vigor due to different seed-priming treatments, no differences were detected in the final grain yield and N response in corn. Seed soaking in water reduced plant stand in 2002, but grain yield was not affected significantly. Seed soaking with 2.5% KCl or 20 ppm GA3 for 16 h was detrimental to corn emergence and early growth while brief soaking in 20 ppm GA3 solution enhanced early growth. Despite these small differences at the seedling stage, they were not reflected in final grain yield. The benefits of seed priming as reported in semiarid environments were not realized in the humid regions of eastern Ontario, possibly due to more wet and cool conditions during the seedling establishment stage and higher soil NO3–N availability. We conclude that in a humid growing environment such as eastern Ontario, seed priming in corn has limited or no benefits on crop development, N response, and grain yield.


   ACKNOWLEDGMENTS
 
The authors gratefully acknowledge the excellent technical assistance of D. Balchin, L. Evenson, V. Deslaurier, and I. Smith. ECORC Contribution no. 04-398.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome