Wheat seeding rate for spread and distinct row seed placement with air seeders

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1 Wheat seeding rate for spread and distinct row seed placement with air seeders Adrian M. Johnston 1 and F. Craig Stevenson 2 1 Potash and Phosphate Institute of Canada, Pinehouse Drive, Saskatoon, Saskatchewan, Canada S7K 5K2 ( ajohnston@ppi-ppic.org); 2 Research scientist, 206A Dunlop St., Saskatoon, Saskatchewan, Canada S7N 2B7. Saskatoon Research Centre manuscript no Received 27 September 2000, accepted 18 May Johnston A. M. and Stevenson, F. C Wheat seeding rate for spread and distinct row seed placements with air seeders. Can. J. Plant Sci. 81: Air (pneumatic) seeding systems that have seed row opener options that spread seed rather than place it in distinct rows may allow producers to uniformly distribute plants and increase seeding rates to improve cereal crop yield. A study was conducted to determine if seed placement configuration influenced hard red spring wheat (Triticum aestivum L.) response to seeding rate. The study was carried out at Melfort, SK, from 1997 to 1999, using three seed configurations (23 cm and 30 cm distinct row with a hoe opener; and a 20 cm spread using a 28 cm sweep on 23 cm row spacing) and four seeding rates (67, 100, 134, and 167 kg ha 1 ). Grain yield increased 6% when seeding rate was increased from 100 (recommended rate) to 168 kg ha 1 in Improved grain yield with increased seeding rates was related to greater kernels head 1. In the 2 following years, yield decreased by 9% when seeding rate was increased from 100 to 168 kg ha 1. Yield reductions in these years were associated with high yield potential (high soil N availability) and lodging, that in turn resulted in decreased kernels head 1 and kernel weight with increased seeding rates. Grain yield did not differ between the sweep and distinct rows, regardless of the seeding rate. Furthermore, the similar yields among the three seed configurations occurred despite lodging being less with sweeps compared with 23 or 30 cm row spacing at the highest seeding rate in The increased distance between wheat plants with sweeps did not improve grain yields as a result of reduced inter-plant competition, regardless of seeding rate. This absence of grain yield differences between the sweep and distinct row placement illustrates the yield stability associated with Canadian hard red spring wheat cultivars through yield component compensation. Key words: Wheat (Triticum aestivum L.), row spacing, seeding rate, lodging, seed placement Johnston, A. M. et Stevenson, F. C Taux d ensemencement du blé pour les semis par étalement et en rangs avec un semoir pneumatique. Can. J. Plant Sci. 81: Les semoirs pneumatiques dotés d un dispositif ouvrant le sillon et étalant les semences au lieu de les placer en rangs précis pourraient autoriser une distribution plus uniforme des plants et un relèvement du taux d ensemencement, ce qui accroîtrait le rendement des cultures céréalières. Les auteurs ont essayé de voir si la manière dont les graines sont plantées modifie la réaction du blé roux vitreux de printemps (Triticum aestivum L.) au taux d ensemencement. L étude s est déroulée à Melfort (Saskatchewan), de 1997 à 1999, et portait sur trois méthodes d ensemencement (en rangs espacés de 23 et de 30 cm avec traceur de sillon à disque et en bande de 20 cm par étalement de 28 cm sur des rangs espacés de 23 cm) et quatre taux d ensemencement (67, 100, 134 et 167 kg ha 1 ). En 1997, le rendement grainier a augmenté de 6 % quand le taux d ensemencement est passé de 100 à 168 kg ha 1. On attribue cette amélioration au plus grand nombre de grains par épi. Quand on a modifié le taux d ensemencement de la même manière les deux années suivantes, le rendement grainier a néanmoins baissé de 9 %, phénomène associé à un potentiel de rendement élevé (forte concentration d azote disponible dans le sol) et à la verse, qui ont réduit le nombre de grains par épi et le poids du grain avec la hausse du taux d ensemencement. Les techniques de semis par étalement et en rangs ne modifient pas le rendement grainier, peu importe le taux d ensemencement. Par ailleurs, on a obtenu un rendement similaire pour les trois méthodes examinées même si, en 1998, la technique par étalement a entraîné moins de verse que celle en rangs espacés de 23 et de 30 cm, au taux d ensemencement le plus grand. L écartement supérieur des plants résultant de l étalement des semences n améliore pas le rendement grainier, car les plants se livrent concurrence davantage, quel que soit le taux d ensemencement. Le fait qu il n y ait pas de modification du rendement grainier malgré la technique d ensemencement démontre la stabilité des cultivars du blé roux vitreux de printemps canadiens attribuable à la compensation du rendement. Mots clés: Blé (Triticum aestivum L.), espacement des rangs, taux d ensemencement, verse, placement des semences 885 High residue clearance air (pneumatic) seeding systems are being adopted in most regions of the Canadian Prairies. Air seeders increase the efficiency of seeding operations because of their ease of filling, and capacity to carry more seed and fertilizer (Read and Dyck 1990). The ability to maintain positive seed to soil contact when seeding through accumulated surface crop residue has also contributed to the increased popularity of air seeders. There are a few configurations (seed placements) commonly used with air seeding equipment: 1) hoe opener with a narrow (2 cm) seed band at a 23 or 30 cm row spacing; and 2) spreading seed 15 to 23 cm under a 28 cm sweep at a 23 to 30 cm row spacing. The hoe configuration is characterized by distinct rows, whereas, the sweep is characterized by dispersed bands of seed. There is reason to believe that a higher seeding rate may improve cereal crop yield when seed is spread rather

2 886 CANADIAN JOURNAL OF PLANT SCIENCE than placed in distinct rows because of reduced inter-plant competition (Deibert 1993). A higher seeding rate can hasten the use of critical resources and the onset of competition between crop plants (Puckridge and Donald 1967). Increasing the average distance between plants through more uniform plant spacing can reduce the intensity of inter-plant competition when seeding rate was increased (Fischer and Miles 1973). The conclusions of a classical review by Holliday (1963), and results of a more recent study (Marshall and Ohm 1987), confirmed that plant arrangements (row spacings) that increased the intra-row distance between plants improved cereal crop yield when seeding rate was increased. In other studies, the combined benefit of reduced row spacing and increased seeding rate was not realized (Fischer et al. 1976; Johnson et al. 1988; Lafond 1994). Research into the potential benefits of alternative row spacing and seeding rate combinations on the Canadian prairies have focused on distinct rows, and not a wide band of seed. The grain yield for direct-seeded winter wheat in northeastern Saskatchewan was maximized with a 9 cm row spacing at a seeding rate of 124 kg ha 1, while at a 36 cm row spacing the optimum seeding rate was 114 kg ha 1 (Tompkins et al. 1991). Direct seeded spring and winter wheat yields in the Thin Black soil zone in southeast Saskatchewan were similar with a wide (30 cm) and narrow (10 cm) row spacing (Lafond 1994; Lafond and Derksen 1996; Lafond and Gan 1999). These same studies showed that increasing wheat seeding rate resulted in higher grain yields through increased heads per unit area. In the semi-arid Brown soil zone of southwestern Saskatchewan, yield and water-use efficiency were greater when wheat was sown with a 20 cm rather than a 30 cm row spacing (McConkey and Miller 1999). An evaluation of spreading seed with an airseeder was conducted in North Dakota using a seeder with 30 cm row spacing (Diebert 1993). In this study spring wheat yield was 32% greater using a 30 cm spread band of seed compared with seed spread 13 cm or a distinct 2.5 cm row. We are not aware of studies that have compared spread and distinct row seed placements at different seeding rates. Air seeding equipment with opener/boot options that spread seed rather than placing seed in distinct rows continues to be popular. Wheat seed placed in spread or distinct narrow rows may reduce inter-plant competition, thus allowing improved yields with higher seeding rates. However, information is not available to allow producers to objectively choose an appropriate seeding rate for such a system. The objective of this study was to determine if seed placement configuration influenced hard red spring wheat response to seeding rate in a direct seeding system in the Thick Black soil zone of Saskatchewan. MATERIALS AND METHODS Site Description and Experimental Design The effect of seed placement and seeding rate was evaluated at Melfort, Saskatchewan, Canada, from 1997 to The site for each year was located on three different fields on the Melfort Agriculture and Agri-Food Canada Research Farm that previously had been sown to pea for the 1997 trial and canola for the 1998 and 1999 locations. Soils at the Research Farm are a silty clay (16% sand, 40% silt, and 44% clay) Orthic Black Chernozem (Udic Haploboroll) with ph 6.4 and 11% organic matter content. The experimental design was a randomized complete block with four replicates. A factorial combination of seed placements (distinct row: 23 cm and 30 cm row spacing with hoe opener; and 20 cm spread band achieved by spreading seed under a 28 cm cultivator sweep on 23 cm row spacing) and four wheat seeding rates (67, 100, 134, and 167 kg ha 1 ) were established in plots 3.7 m by 7.0 m in 1997 or 3.7 m 15.3 m in 1998 and The hard red spring wheat cultivar used was CDC Teal. The same seed lot was used for the 3 yr of the study, and seeding rate adjusted based on germination tests conducted prior to seeding each year. Prior to seeding, urea was banded over the entire site at right angles to the plots using an air seeder with 30 cm row spacing at rates of 19 (1997), 32 (1998), or 29 (1999) kg N ha 1. Urea rates were based on a total (soil residual prior to seeding plus fertilizer) N supply for wheat of 100 kg N ha 1. Plots were seeded with two identical air seeders, with the exception that one had 23 cm row spacing and the other 30 cm row spacing. The sweep treatments were seeded using the 23 cm row spacing air seeder, equipped with 28 cm cultivator sweeps and a spreader boot that spread seed over a 20 cm area. Sweep treatments were packed twice immediately following seeding with a commercial tine harrow and coil packer unit. Monoammonium phosphate fertilizer was seed placed at rates of 12 kg P ha 1 during seeding operations. Weeds were controlled with a tank mixture of Horizon (ICIA 0604 [(2-(cyclohexen 1-one, 2- [1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6- trimethylphenyl)-(9cl))]) + Buctril-M (bromoxynil (3,5-dibromo-4-hydroxybenzonitrile)/MCPA [(4-chloro-2- methylphenoxy)acetic acid]) applied at recommended rates with 110 L ha 1 of water and a surfactant. Wheat seedlings were counted at 3 to 4 wk after seeding in two 1-m sections of crop row for 23 and 30 cm row spacing, and using a 0.5 m 2 quadrat for sweep treatments, within each plot. Grain filled heads were counted using the same area as the seedling emergence just prior to harvest. Lodging was rated in each plot in 1998 and 1999 using a 0 to 9 scale (1 = standing, 9 = completely lodged). Grain samples were harvested from the entire area of each plot with a plot combine, dried to constant moisture, cleaned, and their weights recorded. Grain yields are presented at a moisture content of 14.5%. The weight of 1000 kernels was used to calculate kernel weight. Kernels head 1 were calculated using grain yield, heads m 2, and kernel weight. Statistical Analysis Data were analyzed for each year separately with the PROC MIXED procedure of SAS (Littel et al. 1996), with blocks as a random effect and seed placements and seeding rates as fixed effects. Treatment effects were declared significant at P < 0.05.

3 JOHNSTON AND STEVENSON WHEAT SEEDING WITH AIR SEEDERS 887 Table 1. Mean responses of spring wheat to seed placement and seeding rate at Melfort, SK, Canada in 1997 Seedling density Grain yield Heads Kernels Kernel weight (plants m 2 ) (kg ha 1 ) (no. m 2 ) (no. head 1 ) (mg) Seed placement 23 cm cm Sweep LSD Seeding rate 67 kg ha kg ha kg ha kg ha Seeding rate contrasts Linear < < < < Quadratic ANOVA (P value) Seed placement (P) < < < Seeding rate < < P R CV (%) Table 2. Mean responses of spring wheat to seed placement and seeding rate at Melfort, SK, Canada in 1998 Seedling density Lodging Grain yield Heads Kernels Kernel weight (plants m 2 ) (0 9 scale) (kg ha 1 ) (no. m 2 ) (no. head 1 ) (mg) Seed placement 23 cm cm Sweep LSD Seeding rate 67 kg ha kg ha kg ha kg ha Seeding rate contrasts Linear < < < < Quadratic ANOVA (P value) Seed placement (P) < Seeding rate < < < P R CV (%) Table 3. Mean responses of spring wheat to seed placement and seeding rate at Melfort, SK, Canada in 1999 Seedling density Lodging Grain yield Heads Kernels Kernel weight (plants m 2 ) (0 9 scale) (kg ha 1 ) (no. m 2 ) (no. head 1 ) (mg) Seed placement 23 cm cm Sweep LSD Seeding rate 67 kg ha kg ha kg ha kg ha Seeding rate contrasts Linear < < < Quadratic ANOVA (P value) Seed placement (P) < < < Seeding rate < < < P R CV (%)

4 888 CANADIAN JOURNAL OF PLANT SCIENCE RESULTS AND DISCUSSION Seedling Density The narrower row spacing (23 cm) used in this study provided the highest seedling density, while the 30 cm row spacing always had the lowest density in all years (Tables 1, 2, and 3). Sweeps (spread band) provided the best plant stand in 1997, however, was grouped with the 30 cm rows in 1998 and Seedling density increased linearly with progressively higher seeding rates in all years. A seed placement by seeding rate interaction in 1999 reflected a lack of seedling density response to increasing seeding rate with the sweep opener, while a positive response of density to seeding rate was recorded with the 23 and 30 cm row spacing (Fig. 1c). Lodging While no lodging occurred in 1997, significant lodging was recorded in 1998 and 1999 (Tables 2 and 3). The severity of lodging increased with progressively higher seeding rates and plant populations in both years. A significant seed placement by seeding rate interaction recorded in 1998 reflecting increased lodging up to the highest seeding rate with the 23 and 30 cm row seeding, while increasing the seeding rate from 134 to 168 kg ha 1 did not result in increased lodging with the sweep seed placement (Fig. 2a). Fig. 1. The effect of seed placement and seeding rate on wheat seedling density and grain yield in 1997 (a and d), 1998 (b and e) and 1999 (c and f) at Melfort, Saskatchewan, Canada. The error bars represent the interaction LSD Yield and Yield Components Grain yield increased in 1997, and decreased in 1998 and 1999 as a result of the lodging, with progressively higher seeding rates (Table 1, 2 and 3). The profile of yield reductions across seeding rates in 1998 and 1999 also differed, with yield reductions commencing at the lowest seeding rate in 1998 and at the 100 kg ha 1 seeding rate in With respect to yield components, heads m 2 was not affected by seeding rate in any year, while kernel weight was reduced with increasing seeding rate, and a variable response was recorded for kernels head 1 (Tables 1, 2 and 3). A non-significant decline in head number in 1997 resulted in an increase in kernels head 1 with increasing seeding rate, while the opposite response was recorded in the lodging year Kernel weight decreased with progressively higher seeding rates in all years, especially in 1998 for seeding rates between 64 and 134 kg ha 1. Grain yield did not differ with seed placement in any of the trial years (Tables 1, 2 and 3). Head number reflected the seedling emergence data, and resulted in a corresponding variation in kernels head 1, with a low head number resulting in a higher number of kernels head 1. Heads m 2 were greatest with 23 cm rows and sweeps compared with 30 cm rows in all years, although this effect was most notable in The effect of row spacing on kernels head 1 was opposite to that for heads m 2, illustrating the yield compo-

5 JOHNSTON AND STEVENSON WHEAT SEEDING WITH AIR SEEDERS 889 Fig. 2. The effect of seed placement and seeding rate on lodging in 1998 (a), and heads m 2 (b) and kernels head 1 (c) in 1999 at Melfort, Saskatchewan, Canada. The error bars represent the interaction LSD nent compensation of Canadian hard red spring wheat cultivars in response to seed placement. Kernel weight, for practical purposes, was similar among the three seed placements, the exception being 1999 when a low kernels head 1 with the sweep treatment resulted in an increased kernel weight for this treatment. Significant seeding rate by seed placement interactions were recorded for head number and kernels head 1 in 1999 (Table 3). Both of these interactions were a result of how the 30 cm row spacing treatment responded to increasing seeding rate (Fig. 2b, 2c). Increasing seeding rate resulted in an increase in head number with the 30 cm rows, while no effect was observed for the 23 cm row and sweep placements. Similarly, while the 23 cm rows and sweeps showed no kernels head 1 response to seeding rate, low head numbers with the 30 cm rows resulted in increased kernels head 1 at the lowest seeding rates (Fig. 2c). Seeding Rate and the Environment There were some general observations regarding wheat yield and yield component responses to increased seeding rates. First, in 1997 the positive grain yield response to seeding rate never exceeded 10% in this study (321 kg ha 1 more yield for an increase of 100 kg ha 1 in seeding rate). Where negative grain yield responses to increased seeding rate were measure they ranged from 9 to 14%. Greater interplant competition associated with increased seeding rates may have: 1) caused additional tiller abortion and plant mortality resulting in similar heads m 2 across seeding rates in all years; and 2) reduced resource availability during kernel filling in all years and resulted in lower kernel weight. Seed set appears to have been a critical yield-determining growth period in this study, as indicated by the close correspondence between responses to seeding rate for kernels head 1 and grain yield. A number of other studies have shown that increased seeding rates resulted in greater head number per unit area and less kernels per head, and sometimes slightly lower kernel weight (Joseph et al 1985; Tompkins et al. 1991; Lafond 1994). In this study, environmental conditions and the impact of lodging influenced the pattern and magnitude of yield component compensation and subsequent yield response to increased seeding rate. The effect of seeding rate was dependent on environmental conditions and not the pattern of seed placement. Grain yield responded positively to seeding rate in 1997 because of the absence of lodging conditions. In 1998 and 1999, thundershowers with higher wind velocities coincided with grain filling, a time when wheat plants are susceptible to lodging. Reduced tillering of plants with the highest seeding rates would provide less resistance to lodging (Pinthus 1973). Lodging restricted the flow of resources in the plant during times of head development. In 1998, more severe lodging may have further reduced resource availability and caused the negative trend for kernel weight with increased seeding rates. Producers in sub-humid regions of the Canadian prairies should be aware that excessive N combined with erratic weather conditions that promote lodging, could cause wheat yield reductions with increased seeding rates. Row Spacing and Inter-plant Competition Air seeding equipment producing a spread of seed rather than distinct rows increases the distance between plants, and for this reason should reduce inter-plant competition and allow for greater yields with increased seeding rates. In this study, wheat sown with sweeps had little or no effect on the grain yield of Canadian hard red spring wheat, regardless of the seeding rate. These results are in agreement with those from another study conducted in a sub-humid production region of Saskatchewan (Lafond 1994) that support the use of wider row spacing (30 cm) across a range of seeding rates. Greater inter-plant distance and reduced inter-plant competition of spread band seed placements did not allow increased seeding rates to improve wheat yields in this study, as indicated by previous research (Holliday 1963; Fischer and Miles 1973; Marshall and Ohm 1987). Future research may choose to investigate possible benefits of

6 890 CANADIAN JOURNAL OF PLANT SCIENCE increased seeding rates for spread band compared with distinct rows with other crop types such as barley (Hordeum vulgare L.) and Canadian prairie spring wheat with higher yield potential. While seedling density varied significantly, wheat grain yield was similar between distinct seed placements with hoes and spread band placement with sweeps, even at increased seeding rates. The increased distance between wheat plants with sweeps did not appear to be enough to reduce inter-plant competition. Greater seed spread in the row may be necessary to achieve the reduced levels of interplant competition to improve wheat productivity (Deibert 1993). However, the dispersed plant pattern with sweeps compared with distinct rows provided more canopy support. Better canopy rigidity explains why additional lodging was curtailed with sweeps at higher seeding rates in From these study results we conclude that producers using air seeders can expect currently available opener/boot options, which result in different seed placements, to provide similar levels of productivity within the range of commonly used seeding rates. ACKNOWLEDGMENTS The authors acknowledge the funding from Agriculture and Agri-Food Canada and the expert technical assistance of L. Falk and B. Johnson. Deibert, E. J Spring wheat response to seed spreader patterns and deep band fertilizer placement with an air seeder. J. Prod. Agric. 6: Fischer, R. A. and Miles, R. E The role of spatial pattern in the competition between crop plants and weeds. A theoretical analysis. Math. Biosci. 18: Fischer, R. A., Aguilar, I. M., Mauer, R. O. and Rivas, S. A Density and row spacing effects on irrigated short wheats at low latitude. J. Agric. Sci. (Camb.) 87: Holliday, R The effect of row width on the yield of cereals. Field Crop Abstr. 16: Joseph, K. D. S. M., Alley, M. M., Brann, D. E. and Gravelle, W. D Row spacing and seeding rate effects on yield and yield components of soft red winter wheat. Agron. J. 77: Johnson, J. W., Hargrove, W. L. and Moss, R. B Optimizing row spacing and seeding rate for soft red winter wheat. Agron. J. 80: Lafond, G. P Effects of row spacing, seeding rate and nitrogen on yield of barley and wheat under zero-till management. Can. J. Plant Sci. 74: Lafond, G. P. and Derksen, D. A Row spacing and seeding rate effects in wheat and barley under a conventional fallow management system. Can. J. Plant Sci. 76: Lafond, G. P. and Gan, Y Row spacing and seeding rate studies in no-till winter wheat for the Northern Great Plains. J. Prod. Agric. 12: Littel, R. C., Milliken, G. A., Stroup, W. W. and Wolfinger, R. D SAS System for Mixed Models. SAS Institute, Cary, NC. 656 pp. Marshall, G. C. and Ohm, H. W Yield responses of 16 winter wheat cultivars to row spacing and seeding rate. Agron. J. 79: McConkey, B. G. and Miller, P. R Row spacing effects on plant populations, canopy closure, water use, and grain yields in the Brown soil zone. Pages in Proc. Soils & Crops 1999, University of Saskatchewan, Saskatoon, SK. Extension Division, University of Saskatchewan, Saskatoon, SK. Pinthus, M. J Lodging in wheat, barley and oats: the phenomenon, its causes, and prevention measures. Adv. Agron. 25: Puckridge, D. W. and Donald, C. M Competition among wheat plants sown at a wide range of densities. Aust. J. Agric. Res. 18: Read, W. B. and Dyck, B. F Design considerations for seed and fertilizer openers. Pages in Air Seeding 90, June, Regina, SK. Extension Division, University of Saskatchewan, Saskatoon, SK. Tompkins, D. K., Hultgreen, G. E., Wright, A. T. and Fowler D. B Seed rate and row spacing of no-till winter wheat. Agron. J. 83: