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CROP ECOLOGY, MANAGEMENT & QUALITY

Seeding Rate and Genotype Effect on Agronomic Performance and End-Use Quality of Winter Wheat

^a Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583
^b Dep. of Agronomy, Univ. of Nebraska, Panhandle Research and Extension Center, Scottsbluff, NE 69361
^c Dep. of Biometry, Univ. of Nebraska, Lincoln, NE 68583

* Corresponding author (pbaenziger1{at}unl.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Few experiments have studied how seeding rates affect agronomic performance and end-use quality of modern wheat (Triticum aestivum L.) genotypes in the Great Plains. Higher grain yield and better quality grain production requires the use of appropriate seeding rates. During the 1997 and 1998 crop seasons, 20 winter wheat genotypes and experimental lines were evaluated at two locations (four environments) to assess seeding rate and genotype effects on agronomic performance and end-use quality of wheat. Significant differences among environments, seeding rates, and genotypes, and some of their interactions were identified. Lower seeding rates decreased plant population (by 62.3%), grain yield (by 0.8 Mg ha^-1), kernel weight (by 1.3 mg kernel^-1), flour yield (by 0.8 g/100 g grain), mixing time (by 0.7 min), caused later flowering (by 2 d), and increased flour protein content (by 15 mg g^-1) and mixing tolerance (1 unit). Environment x genotype interactions were significant for all the traits except plant population and mixing tolerance. On the basis of the four environments, the seeding rate x genotype interactions were nonsignificant for all traits except plant height. These results provide evidence that agronomic performance and end-use quality traits are greatly influenced by the environmental conditions and less so by seeding rates. Seeding rate affected plant population, days to flowering, plant height, grain yield, kernel weight, flour yield, flour protein, and mixing time and tolerance of wheat; therefore, seeding rate should be considered as a factor in obtaining higher grain yields with good end-use quality.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
WHEAT IS GROWN in a wide range of environments that affect overall performance, particularly grain yield and end-use quality. Wheat yield and end-use quality depend upon the environment, genotype, and their interaction (Peterson et al., 1998; Eskridge et al., 1994; Baenziger et al., 1985). Environmental factors that may limit productivity and quality of wheat include climatic factors over which producers have little control (such as precipitation, temperature, day length), soil types, and management practices (such as fertilizer, herbicides, fungicides, irrigation, time of sowing, and seeding rate) some of which may partially mitigate other environmental factors.

Management practices play an important role in determining the yield and end-use quality of wheat. Numerous studies have documented how N fertilization, seeding rate, planting date, row spacing, and seeding depth affect yield and yield components of wheat (e.g., Scheromm et al., 1992; Blue et al., 1990; Johnson et al., 1988).

Seeding rate has long been studied as an integral part of wheat production and productivity. Optimal seeding rate has been shown to be higher in high rainfall and irrigated environments (Quisenberry, 1928). Kiesselbach and Sprague (1926) reported a linear increase in grain yield as seeding rate increased from 34 to 101 kg ha^-1 and concluded that a rate of 84 to 101 kg ha^-1 was most practical for eastern Nebraska. Johnson et al. (1965) reported that thinly seeded plots (10, 20, and 40 kg ha^-1), when compared with 81 kg ha^-1 at 30-cm-row spacing, led to later maturity and more winter killing in NE. Johnson et al. (1966) with a similar trial grown under drought conditions at North Platte found a genotype x seeding rate interaction and the 40 kg ha^-1 seeding rate producing the highest yields. Stoltenberg (1968), in a 2-yr study using genotypes grown in 30-cm rows, recommended seeding rates of 17 to 22 kg ha^-1 for winter wheat in western NE, 34 to 39 kg ha^-1 rates in central NE, and no less than 67 kg ha^-1 for eastern NE. Koycu (1968) at Lincoln, NE, reported that 60 kg ha^-1 produced approximately 600 kg ha^-1 more grain than did 30 kg ha^-1. Blue et al. (1990), in a 3-yr study on the influence of planting date, seeding rate, and phosphorus rate on ‘Brule’ wheat in southeastern NE, found that an increase in the seeding rate from 34 to 101 kg ha^-1 increased grain yield by 350 kg ha^-1. The results obtained in NE were similar to those found by Wilson and Swanson (1962) and Stickler et al. (1964) at Hays and Manhattan, KS.

Although the effect of seeding rate on agronomic performance of genotypes has been studied since 1926, little has been published on the effect of seeding rate on end-use quality. The effect of seeding rate on the overall performance of recently released, high-yielding genotypes is also unknown. Thus, it is important to evaluate the effect of seeding rate on agronomic performance and end-use quality of modern genotypes.

The objectives of this study were to evaluate the influence of seeding rate on agronomic performance of modern hard red winter wheat genotypes and to investigate the effect of seeding rates on milling and baking properties of hard red winter wheat genotypes grown in different environments.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Genotypes and Experimental Sites
Fourteen commonly grown winter wheat genotypes from NE and six advanced lines with diverse genetic backgrounds (Table 1) were grown at Lincoln and Mead, NE, in 1997 and 1998. Though some of the genotypes were originally released three to seven decades ago, they have been used again in production in recent years. The soil type was Sharpsburg silty clay loam (i.e., a fine montmorillonitic, mesic typic arguidoll) at Lincoln and Mead. The experimental design within each environment was a randomized complete block design (RCBD) with two replications. A factorial treatment design was used with four seeding rates of 16, 33, 65, and 130 kg ha^-1 and 20 genotypes in 1997. Seeding rates were considered as environments influencing agronomic and end-use quality of wheat. In 1998, kernel weight of each genotype was measured and the same number of kernels were planted per ha as would be planted at 16, 33, 65, 130 kg ha^-1 of ‘Arapahoe’. This change was considered to add precision but had a minor effect because most genotypes had very similar 1000-kernel weight. These seeding rates were 0.25, 0.5, 1, and 2 times the normal seeding rate for eastern NE. The fields were prepared with standard production practices, such as land preparation, fertilizer application, herbicide application, and seed was planted in plots that had four 2.4-m rows with 0.30 m between rows.

To estimate end-use quality, a 35-g sample of grain was taken from each plot and tempered to a moisture basis of 152 g H₂O kg^-1 grain for 18 to 20 h prior to milling. The sample was then milled in a Quadrumat Jr. mill (C.W. Branbender Instruments Inc., South Hackensack, NJ). Flour was separated from bran with a standard shaker (Strand Shaker Co., Minneapolis, MN) at 225 rpm for 90 s with a U.S.A. standard testing sieve No. 70 and the flour was weighed. Flour yield was expressed as grams of flour per 100 g of grain. Flour protein content, expressed as milligram protein per gram flour at a 140 g H₂O kg^-1 flour moisture basis, was determined by the Udy dye binding (Udy dye Method 46-14A) and periodically checked using a Crude Protein-Combustion method (American Association of Cereal Chemists, 1983).

Mixograph analysis was performed with a National Manufacturing Mixograph (Lincoln, NE) and a 10-g sample and constant water absorption of 620 g H₂O kg^-1 flour. Mixing time was recorded as the time in minutes to maximum Mixograph curve height. Mixing tolerance was determined on the basis of comparisons with standard Mixograph curves in the Nebraska Wheat Quality Laboratory and scored by a scale from 0 to 7 with higher scores indicating greater tolerance of dough to overmixing (Method 54-40; American Association of Cereal Chemists, 1983).

The data were analyzed by PROC GLM (SAS Institute, 1994). Homogeneiety of variance tests were done before combining across environments in the combined ANOVA. In this study, locations and years were considered random environments in the combined analysis of variance.

Environments and replications were considered random effects and seeding rates and genotypes were considered fixed effects. The respective error terms for F-test were estimated by meansof the random statement with test option in PROC GLM to detect significant differences among main effects and interactions. Means statement was used for calculating treatment means, and Fisher's least significance difference (P = 0.05) was used for comparing the mean differences.

Polynomial regression was used on trait means for each seeding rate averaged over genotypes to develop equations on how seeding rates affect the traits. Optimum seeding rate was determined by inverse polynomial regression for each trait with the use of orthogonal polynomial contrasts from the ANOVA to determine the degree of the polynomial for regression equations (Draper and Smith, 1981).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Differences among environments, seeding rates, and genotypes were observed for agronomic performance and end-use quality traits (Table 2) with the exception of plant population and flour yield x environment interaction. This indicates agronomic performance and end-use quality were significantly affected by the growing conditions (environments and seeding rates) and genotypes. No difference due to environment for plant population implies that the average stands were similar in the two environments (in 1997) where this trait was measured. The environment and seeding rate influenced all traits.

All traits except plant height had environment x seeding rate interactions (Table 2). The interaction appeared to be due mainly to changes in magnitude, rather than to changes in order, except for grain yield. In three of four environments, grain yield increased linearly with increasing seeding rate (Fig. 1) . However, in the Lincoln 1998 environment, there was a mild winter and higher seeding rates which resulted in lower grain yields. ‘Mead’ had more winter and frost killing in 1997, and therefore lower plant populations that resulted in lower grain yield. If the environment is conducive, wheat genotypes have the ability to compensate under relatively lower seeding rates to establish good stands with many tillers, larger heads, or more kernels, resulting in higher grain yield.

View larger version (19K): [in this window] [in a new window]   Fig. 1. Mean grain yield of 20 winter wheat genotypes grown at Lincoln 1997 (L97), Mead 1997 (M97), Lincoln 1998 (L98), and Mead 1998 (M98) Nebraska environments.

Seeding Rate Effects on Agronomic and End-Use Quality of Winter Wheat
An increase in seeding rate was found to increase plant population (in 1997), plant height, grain yield, and grain volume weight averaged over genotypes (Table 3). Reducing seeding rates placed a greater reliance on a genotype's ability to compensate for fewer plants, particularly by increasing the number of harvested kernels per square meter through increasing the number of spikes per square meter or kernels per spike. Mean days to flowering decreased as seeding rate increased, although this effect varied with the genotype. An increase in seeding rate resulted in proportionally more main culms, which normally flower earlier than do the secondary tillers. The greater the proportion of main culms in the plot, the earlier the plot appeared to be. This result was in agreement with the findings of Wilson and Swanson (1962) and Johnson et al. (1965), who found later maturity in thinly seeded plots. Prodigious tillering resulting from reduced seeding rates may also be the cause of variable and delayed maturation (Thompson et al., 1993) which in term resulted in the crop being uneven and more difficult to manage and harvest.

The highest grain yield averaged over environments and genotypes was obtained at the higher seeding rates (65 and 130 kg ha^-1), with the exception of the Lincoln—1998 (L98) environment, where the highest grain yield was obtained at 33 kg ha^-1 (Fig. 1). Mean grain yield increased up to 65 kg ha ^-1, which was not significantly different from the yield at 130 kg ha^-1 seeding rate (Table 3). These seeding rates produced 33% more grain yield than those seeded at 16 kg ha^-1 (Table 3). Similarly, Sahs (1970) over a 2-yr period, found 37% more grain yield from wheat seeded at 67.2 kg ha^-1 compared with the 22.4 kg ha^-1 seeding rate. Sharma and Smith (1987) at Stillwater and Lahoma, OK, and Stickler et al. (1964) at Manhattan KS, also reported that higher seeding rates (i.e., 67.2 and 123 kg ha^-1, respectively) resulted in higher grain yields and earlier maturity of wheat.

In general, kernel weight increased with increasing seeding rates up to 65 kg ha^-1, although this increase is not significantly different from the average weight obtained at 33 kg ha^-1 (Table 3). Grain volume weights were least when planting rate was 16 kg ha^-1 but increased at higher seeding rates (i.e., 65 and 130 kg ha^-1, Table 3). This result agreed with those of Wilson and Swanson (1962) and Sahs (1970), and this result may have been caused by the presence of additional secondary tillers that delayed maturity and reduced kernel uniformity at lower seeding rates. The later tillers produce smaller grains that result in low grain volume weight. Samuel (1990) also found that grain volume weights increased as the seeding rates were raised from approximately 90 to 270 kg ha^-1, but the effects were slight.

Flour yield increased with increased seeding rates up to 65 kg ha^-1, which was similar to flour yield at the 130 kg ha^-1 seeding rate (Table 3). Flour protein content decreased with increased seeding rate up to 130 kg ha^-1. This result confirms the findings of Samuel (1990), who stated that protein concentration declined as seeding rates and yields increased. However, Campbell et al. (1991) reported that seeding rate has no effect on grain protein concentration. The higher protein content at lower seeding rate could be explained by less competition among plants for nitrogen. In contrast, at higher seeding rates, there would have been strong competition among plants for nitrogen since no extra fertilizer was applied in this experiment at higher seeding rates. The higher grain yields obtained at relatively higher seeding rates imply that more carbohydrate was produced and stored in the grain.

Mixing time of wheat increased with increased seeding rate up to 65 kg ha^-1, with no significant increase at the 130 kg ha^-1 rate. The lower seeding rate resulted in higher protein content and shorter mixing time. Mixing tolerance significantly decreased as seeding rate increased up to 65 kg ha^-1. The mixing time and tolerance result may be explained by the protein content of the seeding rate treatments.

Achieving higher agronomic performance and better end-use quality requires management practices such as seeding rates to be carefully optimized and periodically reviewed. Seeding rate is a predictable environmental variable that affects many agronomic and end-use quality traits of wheat. Therefore, to obtain high grain yields with good end-use quality, seeding rate must be understood. On the basis of the shape of the response curve, the optimum-seeding rate for each trait averaged over genotypes varied (Table 3). Seeding rate significantly affected some of the traits.

Genotype Performance
Predominantly modern genotypes and a few historical genotypes were used in the study to ensure that the genotypes had diverse genetic backgrounds and that the modern and older genotypes varied greatly for the traits measured. The estimated plant population of the genotypes ranged from 51% for Arapahoe to 78% for ‘Pronghorn’ (Table 4). Both genotypes were among intermediate groups in their yield performance across the seeding rates and environments. The genotypes had a 1-wk interval for days to flowering. The average height of the genotypes ranged from 75 to almost 99 cm. Mean grain yield of the genotypes across seeding rates ranged from 2.3 to 3.3 Mg ha^-1 (Table 4). ‘NE92662’, ‘Niobrara’, ‘NE92628’, ‘NE92646’, ‘NE93405’, and ‘Windstar’ were among the top yielding genotypes with an average yield of over 3.1 Mg ha^-1 across all environments and treatments including seeding rates. In contrast, ‘Scout 66’, ‘Cheyenne’, ‘Buckskin’, ‘Centura’, ‘Vista’, and ‘Karl 92’ were genotypes with relatively, lower yields. Thousand-kernel weight and grain-volume weight ranged from 26.4 to 34.7 g and 70.9 to 74.4 kg hL^-1, respectively. NE93405 was the highest in performance for both of the traits while ‘NE91631’ was among the lowest.

Whether older or modern, short or tall, genotype response to seeding rates was similar, implying that recommended seeding rate developed for historical genotypes can be used for modern genotypes, despite their diverse genetic backgrounds.

In summary, seeding rate had less effect on agronomic performance and end-use quality of wheat than did environmental factors. The recommended seeding rate of 65 kg ha^-1 was not the best rate for plant population, days to flowering, flour protein, and mixing tolerance. Genotypes responded similarly to seeding rates, implying that the recommended seeding rate developed for historical genotypes can be used for modern genotypes or advanced lines, despite their diverse genetic background. Most quality traits were low when grain yields were high. At higher seeding rates, more fertilizer could be required for better grain yield and end-use quality of wheat. Higher seeding rates decreased the proportion of secondary tillers. Seeding rate is a predictable environmental factor that affects some agronomic and end-use quality traits of wheat; therefore, it should be studied carefully to obtain higher grain yields with relatively better end-use quality. The non-significant mean values of some traits at higher seeding rates (65 and 130 kg ha^-1) indicate the optimum seeding rate is between those two seeding rates. Further study is needed at rates between 65 and 130 kg ha^-1. On the basis of the response curves, optimum seeding rate for grain yield was about 118 kg ha^-1; for plant height it was 87 kg ha^-1; for grain volume weight, flour protein, and mixing time it was about 97.5 kg ha^-1; and for mixing tolerance and 1000-kernel weight it was 59 and 64 kg ha^-1 respectively. At present, the recommended seeding rate is 65 kg ha^-1 for eastern NE is still appropriate. Optimum seeding rate was environment-specific because of fluctuations in moisture and winter survival.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Nebraska Agric. Res. Division, J. Series No. 13200.

Received for publication January 17, 2001.

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