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CROP ECOLOGY, MANAGEMENT & QUALITY

Planting Date and Nitrogen Effects on Grain Yield and Protein Content of Spring Wheat

Agric. and Agri-Food Canada, Eastern Cereal and Oilseed Research Center (ECORC), Central Experimental Farm, K.W. Neatby Building, 960 Carling Ave., Ottawa, ON, Canada, K1A 0C6

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

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
High grain yield with adequate protein concentration is an important goal for spring wheat (Triticum aestivum L.) production. A field experiment conducted at two sites representing sandy loam and clay loam soils in Ottawa during 2003 and 2004 examined the effects of planting date and nitrogen (N) management on grain yield and grain protein concentration (GPC) in spring wheat. Cultivar AC Brio was planted at three dates at about 10 d intervals starting from the last week of April. Five N treatments were 0, 60, and 100 kg N ha^–1 applied as preplant, 60+40 (preplant + topdress at boot stage), and 60 + 40 kg N ha^–1 (preplant + foliar spray at boot stage). Both planting date and N had significant effects on grain yield and GPC. When planting was delayed beyond mid-May, grain yield was reduced by 15 to 45% in three out of four site-years. However, GPC increased by 6 to 17% in all late planting dates than the early plantings. Grain yields were increased with N application, but there was no benefit due to split N application as topdress or foliar spray than a single application at 100 kg N ha^–1. Regardless of application method, GPC was greater with 100 kg N ha^–1 than with 0 or 60 kg ha^–1, and GPC was more responsive to applied N in a sandy loam soil than in the clay loam soil. Results of this study suggest that it is likely to achieve the target GPC in spring wheat without a significant reduction in grain yield if wheat is planted before the middle of May, especially in clay loam soil.

Abbreviations: CLS, clay loam site • DW, dry weight • GPC, grain protein concentration • GS, growth stage • HI, harvest index • SLS, sandy loam site

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
PLANTING date is one of the most important agronomic factors involved in producing high yielding small grain cereal crops (McLeod et al., 1992). There are several studies that documented the effects of planting date on winter cereals (e.g., Baron et al., 1999; Chen et al., 2003; Schwarte et al., 2005), but studies on the effect of planting date on grain yield and GPC of spring wheat are limited, especially in the more humid environments such as eastern Ontario. Wheat yields in eastern Canada are limited due to a short grain filling period (<40 d). The optimum planting time for wheat in this region is considered to be within the first week of May. Cold temperatures and wet soils during April to early May often prevent timely planting. Heading and grain filling of the late-planted crop generally occurs in warmer periods, and this crop often has reduced duration of grain filling and lower yield. Under such conditions, whether or not adjustment in planting date and N application affect the duration of grain-filling, grain yield, and GPC of spring wheat has not been studied.

Nitrogen plays an important role in supporting grain yield and GPC of wheat (Alkier et al., 1972; Gauer et al., 1992; Rawluk et al., 2000; Ehdaie and Waines, 2001). Grain protein is an important factor that influences the milling and baking quality of wheat (Woolfolk et al., 2002), and N is the major nutrient that influences GPC (Bly and Woodward, 2003). Synthesis of protein in wheat grains depends on uptake of soil N before flowering, continual uptake during the grain filling, and remobilization of stored vegetative N before flowering (Van Sanford and MacKown, 1987; Fischer, 1993). Grain protein concentration of 128 mg g^–1 is considered as a reliable indicator of low N sufficiency in wheat (Selles and Zentner, 2001).

Fertilizer N in Canada is most commonly applied to spring wheat at time of planting and occasionally supplemented with split doses of top-dress before or at flowering (Ayoub et al., 1994; Ma et al., 2006). Preplant applied N is subject to leaching and prone to denitrification or immobilization before plant uptake, thus affecting N use efficiency. Several studies have explored the timing and methods of N application in spring wheat elsewhere. Langer and Liew (1973) reported that percentage grain N in wheat was increased with lateness of N application. Mi et al. (2000) investigated the effect of postanthesis N application to N-uptake and GPC. They found that additional N application during flowering could increase postanthesis N uptake and GPC but the degree of increase differed with cultivars. Their results were consistent with those of Van Sanford and MacKown (1987) and Spiertz and de Vos (1983), who found that crops with higher yield potential may require additional N after anthesis to increase GPC. Bly and Woodward (2003) observed that post-pollination N application gave the highest GPC. López-Bellido et al. (2005) observed a much higher utilization of late season applied N in a Mediterranean environment; average recovery of the applied N in wheat ranged from 14% when applied at sowing to 55% when applied as top dressing at the beginning of stem elongation. Similarly, several other researchers including Powlson et al. (1989), Wuest and Cassman (1992), Ayoub et al. (1994), and Woolfolk et al. (2002) concluded that fertilizer N application near flowering is effective to increase post-flowering N uptake, grain yield, and GPC. On the other hand, some other studies have reported that additional N applied postanthesis increased N uptake but did not increase GPC (Van Sanford and MacKown, 1987; Heitholt et al., 1990; Ehdaie and Waines, 2001). In addition, Strong (1982) found that additional N applied after flowering produced wheat with low GPC. Heitholt et al. (1990) and Rawluk et al. (2000) also reported that vegetative N contributed significantly more to GPC than postanthesis N; additional N at anthesis did not affect grain yield, total grain N and tissue N concentrations. Therefore, reports on N uptake near and after heading and its partitioning to grain are variable and decisions regarding N rates and application timing pose a challenge to farmers.

The efficiency of soil-applied and foliar-sprayed N in terms of grain yield, GPC, and N recovery has also been extensively studied, however, conclusions vary considerably. Gooding and Davies (1992) reviewed the fate of the foliar-applied urea in cereals and showed apparent benefits especially when foliar N was applied before flag-leaf emergence, and when N availability in the soil was limiting. Smith et al. (1991) observed positive increases in GPC with foliar N application, and greater increase in GPC was obtained when the application was made close to flowering. However, Readman et al. (2002) reported no additional yield advantage of foliar-sprayed urea as compared to the soil applied fertilizer. Woolfolk et al. (2002) concluded that late season foliar N applications before or immediately after flowering may significantly enhance GPC in winter wheat. Although Ma et al. (2006) found that foliar application of N at 10 kg ha^–1at the boot stage on top of 90 kg N ha^–1 as preplant significantly increased GPC, but the N-use efficiency was always greater when all N was applied at wheat planting.

The recovery of foliar-applied N at the later stages of wheat development has been assessed using Isotopic ¹⁵N labeling (Powlson et al., 1989; Smith et al., 1991; Rawluk et al., 2000; Readman et al., 2002). Powlson et al. (1989) at Rothamsted, UK reported a recovery of about 70% of the foliar-applied N given at anthesis in the aboveground parts, including 64% in grains. Ma et al. (2006) observed an increased GPC in spring wheat due to foliar-applied N. However, in the Canadian Prairies, Rawluk et al. (2000) showed that the recovery of foliar-applied N on wheat grain ranged from 5.5 to 26.7% compared to 32.3 to 70.1% for soil-applied N, and GPC was higher when urea-N was soil-applied rather than foliar-applied.

The period of grain filling for wheat is often associated with increasing ambient temperatures and diminishing moisture conditions (Panozzo and Eagles, 1999). Photosynthetic green area duration has been associated frequently with yield in wheat (Slafer and Savin, 1994). Nitrogen application has a large effect on leaf area duration (Langer and Liew, 1973). To what extent the rate, time, method of N application, and time of wheat planting affects the duration of grain filling of spring wheat in the limited growing-season of eastern Canada has not been studied. We hypothesized that split-application of N at flowering would extend the duration of grain filling, and yield and GPC can be improved through proper choice of planting date combined with appropriate N application timing and rates. The objective of this study was to determine the effects of planting date and N fertilization rates, timing, and methods on the grain yield, yield components, and GPC of spring wheat under the temperate humid conditions of eastern Canada.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Experimental Site and Treatments
A field experiment was conducted for two growing seasons (2003 and 2004) at two sites representing sandy loam (SLS) (Endoquolls) and clay loam (CLS) soils (Eutrocryepts) each year (Table 1). The two sites were approximately 15 km apart in Ottawa, Canada (45°17' N, 75°43'' W for SLS, and 45°17' N, 75°45'' for CLS). The experiment at SLS was conducted in different sections of the same field in 2 yr, while at CLS, the experiment was conducted in two different fields located about 1 km apart. Wheat was the preceding crop at each site. Before fertilizer application, soil samples (0–30 cm) were taken from each block and analyzed for major plant nutrients, soil organic matter, and soil pH (Table 1).

Measurements
Time until seedling emergence, GS 45, completion of heading (GS 59), anthesis (GS 69) and physiological maturity (GS 93) were recorded. The number of tillers and spikes (i.e., ears or heads) from 1-m row of the third row of each plot were counted at GS 93 and harvested at ground level. Samples were dried at 80°C for >72 h and dry weights were recorded. Grains were separated from the straw and harvest index (HI, i.e., the ratio of grain dry weight to total dry weight) was determined. Similarly, the grain dry weight of an individual spike was calculated based on the number of spikes harvested to the total grain dry weight from the 1 m row length. Eight central rows of each plot were combine-harvested to obtain grain yield. Subsamples of grain were taken and oven-dried to 80°C for >72 h. Grain yield was corrected to 135 g kg^–1 moisture. Grain samples were ground to pass through a 1-mm sieve and were analyzed using a micro-Kjeldahl method (Jones, 1991) for N determination. Grain protein concentration was calculated from the percent N concentration in grain multiplied by a conversion factor of 5.7.

Statistical Analysis
Annual data for each site were subjected to analysis of variance (ANOVA), using the general linear model (SAS Institute, 1996). Treatment mean differences within each site-year were separated using the Fishers' protected least significant difference (LSD) test at P 0.05.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Weather Conditions
Air temperatures during the first planting date averaged 10 ± 1.2°C in both years, while the mean air temperature during the growing season remained between 15 and 23°C in 2003, and 16 and 20°C in 2004. Relative humidity was between 80 and 85% from heading to maturity in both years. In 2003, the seasonal precipitation was about 300 mm for all planting dates at both sites except for the last planting date at CLS, which received only about 250 mm precipitation (Fig. 1 ). In 2004, all of the planting dates received a similar amount of rain (200 mm). Although the total rainfall was greater in 2003 than in 2004, the rainfall was more evenly distributed during the growing season of 2004.

View larger version (65K): [in this window] [in a new window]   Fig. 1. Total precipitation (mm) at 10 d intervals during the growing seasons of 2003 and 2004 at Site-1 (SLS) and Site-2 (CLS). The arrows indicate time of planting and 50% heading stage for different planting dates in each site-year.

Nitrogen treatment had a significant effect only on time to reach GS 93. In all cases, the crop with zero-N matured significantly earlier than the other N treatments (96–98 d vs. 99–102 d). There were no differences in the duration of grain filling (i.e., from GS 59–GS 93) due to N application or planting date (data not shown). It was hypothesized that the application of N at a higher rate or split application of N at boot stage might extend the grain filling period of wheat. However, no benefit from split application of N was evident. There might have been confounding effects of various environmental factors (i.e., mainly temperature and moisture) on the phasic development of wheat, therefore, the effect of N amendments was not significant.

Yield Components
At SLS, the first planting date had more spikes m^–2 than the other two planting dates (Table 3). The second planting date had a lower number of spikes than the first and third planting dates at CLS. The grain DW on the individual spike was also affected by the planting date in all site-years (Table 3). The late planting date resulted in significantly lower grain DW than the other two planting dates and especially at CLS in 2003. However, the mid-planting date at both sites had lower grain DW than the early planting date in 2003.

Grain Yield
Yields were greater in 2003 than in 2004 at both sites (Fig. 2 ). Mean grain yields tended to be greater at CLS compared to SLS. There were no planting date x N treatment interactions for grain yield. Planting date had significant effects on grain yield in both years at SLS and only in 2003 at CLS (Fig. 2). The third planting date had 15 to 45% lower grain yields than the previous two dates, but there was no significant reduction in grain yield due to late planting at CLS in 2004. Except for SLS in 2004, grain yields in the first and second planting dates were similar in all site-years. Planting was too late for the third planting at CLS in 2003. As a result, yields were very small compared to the other dates.

View larger version (33K): [in this window] [in a new window]   Fig. 2. Effect of planting date on the grain yield of wheat at two sites in 2003 and 2004 growing seasons. The bars labeled with different letters within each site-year are significantly different at P 0.05. The D1, D2, and D3 are the first, second, and third planting dates, respectively, for each site-year.

In 2003, differences among N treatments were observed only between the control and the fertilized treatments at both sites (Fig. 3 ). In 2004, the control treatment had the lowest grain yield at both sites and the N₃ treatment produced the highest grain yield. At CLS, grain yields for the N₂, N₃, and N₄ treatment were similar. Although treatments N₃, N₄, and N₅ received the same amount of N (100 kg ha^–1), the yields in N₄ and N₅ were significantly lower than N₃ at SLS, and significantly lower for N₅ than N₃ at CLS, indicating that split-application of N as top-dress or foliar spray did not improve yields compared to preplant applications. The nonsignificant effect of foliar or topdress N applications might have been due to the fact that there was no or very small yield increase between 60 and 100 kg N ha^–1; a similar grain yield was achieved with 60 kg N ha^–1 compared with 100 kg N ha^–1 in three out of four site-years. The foliar applied N treatment showed some leaf burning symptoms immediately following application, but this apparently did not result in reduction in grain yield and other parameters as compared to the top-dressed treatment (i.e., N₄).

View larger version (40K): [in this window] [in a new window]   Fig. 3. Effect of nitrogen application rate, timing, and method on the grain yield of wheat at two sites in 2003 and 2004 growing seasons. The bars labeled with different letters within each site-year are significantly different at P 0.05. The nitrogen treatments are: N1, 0 kg N; N2, 60 kg N ha–1 applied at planting; N3, 100 kg N ha–1 applied preplant; N4, 60 kg N ha–1 applied preplant and 40 kg N ha–1top-dressed at boot stage; and N5, 60 kg N ha–1 applied at planting and 40 kg N ha–1 foliar sprayed at boot stage.

Grain Protein Concentration and Nitrogen Accumulation
Mean GPC values were greater at CLS (141 to 165 g kg^–1) than at SLS (119 to 138 g kg^–1) in both years. The GPC was also different between the 2 yr: GPC was greater in 2003 than in 2004 (Fig. 4 and 5 ). Planting date and N treatment significantly affected GPC such that the later the crop was planted the greater was the GPC in all site-years (Fig. 4). This might be associated with the fact that late planted crop had lower yields than the normal (i.e., first week of May) or earlier planting dates, resulting in similar amounts of N translocated to fewer grains. However, in 2004, at the CLS, there was no difference in grain yield among the three planting dates (Fig. 2), but the second and third planting dates had significantly greater GPC than the first planting date (Fig. 4). The third planting date had a significantly lower grain yield than the other two planting dates at SLS in 2003, but there was no difference in the total N content in grain (Fig. 6 ). This indicates that the late planted crop tended to accumulate more N in grain than the early planted crop. Selles and Zentner (2001) reported that under low water stress, as grain yield decreased, GPC increased. Panozzo and Eagles (1999) concluded that under stressed conditions, higher rates of accumulation of grain N and lower rates of accumulation of carbohydrate were primarily responsible for increased GPC. Ehdaie and Waines (2001) observed that although the early planted crop removed more N from the soil than when the crop was planted on the optimum date, partitioning of N to grain was greater in the late planted crop. They also reported that on average, plants lost more N from anthesis to maturity at early than optimum planting date. A possible explanation could be that in our study also, the early planted crop lost more N through senesced leaves and root than the later planted ones, thus they had lower GPC than the later planted crops. Heitholt et al. (1990) reported that vegetative N contributed significantly more to grain N than postanthesis N. If the vegetative N had more contribution to grain protein, then the early planted crops should have greater GPC than the late planted crop. Nevertheless, such effect was not observed in this study.

View larger version (28K): [in this window] [in a new window]   Fig. 4. Effect of planting date on the grain protein concentration (g kg–1) of spring wheat at two sites in 2003 and 2004. The bars labeled with different letters within each site-year are significantly different at P 0.05. The D1, D2, and D3 are the first, second, and third planting dates, respectively, for each site-year.

View larger version (39K): [in this window] [in a new window]   Fig. 5. Effect of nitrogen rates on the grain protein concentration (g kg–1) at two sites in 2003 and 2004 growing seasons. The points labeled with different letters within each site-year are significantly different at P 0.05. The nitrogen treatments are: N1, 0 kg N; N2, 60 kg N ha–1 applied preplant; N3, 100 kg N ha–1 applied preplant; N4, 60 kg N ha–1 applied preplant and 40 kg N ha–1 topdressed at boot stage; and N5, 60 kg N ha–1 applied preplant and 40 kg N ha–1 foliar sprayed at boot stage.

View larger version (32K): [in this window] [in a new window]   Fig. 6. Effect of planting date on the N accumulation (kg ha–1) in the grain yield of wheat at two sites in 2003 and 2004 growing seasons. The bars labeled with different letters within each site-year are significantly different at P 0.05. The D1, D2, and D3 are the first, second, and third planting dates, respectively, for each site-year.

Although total N content in the grain was affected by planting date and N treatments, the overall N content in grain was much greater in 2003 than in 2004, and greater at CLS than SLS (Fig. 6). The greater grain N content in 2003 than in 2004 was associated with greater grain yields in 2003. Despite a difference in GPC among planting dates, differences in the grain N content were not seen in 2003 at SLS and in 2004 at CLS (Fig. 6). As expected, N treatment had significant effects on grain N uptake in all site-years (Fig. 7 ). However, the response of N content in grain to N treatment was much greater at CLS than at SLS. At both sites, the N₃, N₄, and N₅ treatments resulted in similar amounts of N in grain in 2003, but N₃ had greater N than N₄ at SLS and than N₄ and N₅ at CLS in 2004. The grains with 0 N treatment had the lowest N content followed by N₂ in all site-years.

View larger version (40K): [in this window] [in a new window]   Fig. 7. Effect of nitrogen treatments on the N accumulation in the grain yield of wheat (kg ha–1) at two sites in 2003 and 2004 growing seasons. The bars labeled with different letters within each site-year are significantly different at P 0.05. The nitrogen treatments are: N1, 0 kg N; N2, 60 kg N ha–1 applied preplant; N3, 100 kg N ha–1 applied preplant; N4, 60 kg N ha–1 applied preplant and 40 kg N ha–1 top-dressed at boot stage; and N5, 60 kg N ha–1 applied preplant and 40 kg N ha–1 foliar sprayed at boot stage.

The GPC tended to be higher at CLS compared to SLS. Residual soil N at CLS was higher than at SLS initially (Table 1). The coarse textured soil of the SLS was expected to be more prone to leaching than CLS. Moreover, the higher organic matter content in the soil of CLS might have also resulted in greater mineralization. These factors may have contributed to the difference in response of GPC to applied N between the two sites. Higher N treatments also resulted in greater GPC (Fig. 5). Similarly, GPC responded to applied N irrespective of timing and method of N application, but response of applied N to GPC was greater at the coarse textured soil than the fine textured soil.

When wheat was planted until 16 May in clay loam soil, there was no yield reduction and GPC was greater than the earlier planting dates. Even in the sandy loam soil, the second date of planting (9 May) resulted in a similar grain yield and GPC in 2003 season. The grains with higher GPC pay farmers more than the grains below the prescribed level of GPC (i.e., 125 g kg^–1). If the monetary value of yield is calculated, according to the Ontario Wheat Producer's Marketing Board, the grains exceeding 125 g kg^–1 GPC will get CAN $18.0 premium for each ton of grains. There appears to be a potential for increased net benefit with spring wheat if the crop is planted before the second week of May and supplied with adequate N fertilizer at the time of wheat planting.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Planting before 9 May in a sandy loam soil and the second week of May in a clay loam soil would help to optimize wheat yield under the humid conditions of eastern Canada. The GPC tended to be greater with delayed planting in both soil types. Under conditions where normal planting is hampered due to factors such as unsuitable weather conditions, the higher GPC might compensate for some of the yield loss (up to 150 kg ha^–1) due to late planting. Response of spring wheat to applied N was small and no advantage of split-application of N was observed over a single dose of preplant application in terms of grain yield and GPC. Similarly, there were no benefits of foliar or topdressed N applications at GS 45 over a single application at planting. Planting wheat before mid-May coupled with an optimum N fertilization strategy, may maximize production efficiency and overall economic benefit. The differences between the two sites in the level of grain yield and response of GPC to N might be related to those gross characteristic differences and it was not possible to trace the soil differences based on these results. Additional research might provide more conclusive evidence of a need to vary N recommendations based on certain soil measurements.

	ACKNOWLEDGMENTS

 
The authors gratefully acknowledge the excellent technical assistance of L. Evenson, Y. Chen, D. Balchin and V. Deslauriers. ECORC contribution No: 05-568.

Received for publication February 15, 2006.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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