W. E. May

Structural equation modeling in the plant sciences: An example using yield components in oat

Lamb, E. G., Shirtliffe, S. J. and May, W. E. 2011. Structural equation modeling in the plant sciences: An example using yield components in oat. Can. J. Plant Sci. 91: 603-619. Structural equation modeling (SEM) is a powerful statistical approach for the analysis of complex intercorrelated data with a wide range of potential applications in the plant sciences. In this paper we introduce plant scientists to the principles and practice of SEM using as an example an agronomic field trial. We briefly review the history of SEM and path analysis and introduce the statistical concepts underlying SEM. We demonstrate the use of observed and latent variable structural equation models using a multi-site multi-year field trial examining the effects of seed size and seeding density on the plant density and yield of oat in Saskatchewan. Using SEM allowed for insights that a standard univariate analysis would not have revealed. We show that seeding density has strong effects on plant and panicle density, but has very limited effects on final yield. Plant density has a consistent non-linear effect on panicle density across location that was not affected by precipitation. In contrast, the implicit effect of precipitation on seed number appears to be the main driver for final yield. Incorporating precipitation data into the model demonstrates how mechanistic models can be developed by including in the path diagram variables that would normally treated as random factors in a mixed model analysis. Finally, we provide a guideline to assist plant scientists in determining whether SEM is an appropriate method to be used for the analysis of their data.

Field pea seeding management

The impact of seed placement and seeding rate on crop yield is not clearly understood for field pea (Pisum sativum L.). A field experiment was conducted at Melfort, SK, and Lacombe, AB, in 1998 and 1999, to evaluate the effect of three seed placements (distinct row: 23 cm and 30 cm with a hoe opener; and spread band: a 20-cm spread using a 28-cm sweep on a 23-cm row spacing) and three seeding rates (50, 100, and, 150 seeds m-2) on pea seedling density, seed yield and seed weight of a leafy prostrate and semi-leafless upright cultivar. A follow-up experiment was conducted at seven sites across Saskatchewan in 2001 to further examine the influence of a wider range of seeding rates (20, 30, 40, 50, 60, 70, 80, 90, 100, and 120 target plants m-2). Pea productivity for both cultivars was not affected by the different seed placements, despite a 4 mg greater seed weight for distinct row seed placements compared with spread band placement across all 1998–1999 sites. Moreover, the absence of a seed placement by se...

Adaptation of oilseed crops across Saskatchewan.

Differences in response to nitrogen (N) fertilizer will affect the production economics of field crops. Currently, there is limited information comparing the agronomic and economic performance of juncea canola (Brassica juncea L.) and sunflower (Helianthus annuus L.) to napus canola (Brassica napus L.) and flax (Linum ustitatissimum L.) in Saskatchewan under no-till practices. A study of these species was carried out at five Saskatchewan locations over 3 yr and included eight nitrogen rates. All four species had a curvilinear increase in grain yield as N rate increased with the largest yield response observed in napus canola to as much as 200 kg N ha-1. The majority of the increase in flax grain yield occurred as the N rate increased from 10 to 90 kg ha-1, while most of the increase in grain yield of juncea canola and sunflower occurred as N increased from 10 to 70 kg ha-1. Biplot analysis indicated that grain yield variation was reduced at and above 50 kg N ha-1 in flax, napus canola and juncea canola, b...

Effect of nitrogen, seeding date and cultivar on oat quality and yield in the eastern Canadian prairies

The proportion of oat (Avena sativa L.) being used for race horses and human consumption has increased over the past 15 yr. The objective of this study was to evaluate the effects of N, seeding date and cultivar on grain yield components, grain yield and grain quality of oat under a direct seeding system. Four N rates, three seeding dates and two cultivars were tested at Indian Head, Melfort, and Canora, SK, and Brandon, MB. Yield was more responsive to increasing N rates from 15 and 80 kg ha-1 when oat was seeded in early May versus early June. Panicles plant-1 was the yield component that accounted for most of the yield increase achieved from increasing rates of N, while kernel weight was the yield component that decreased as the rate of N increased. Physical seed quality decreased (plump seed decreased and thin seed increased) with delayed seeding and greater N fertilizer rates. Nitrogen fertilizer and seeding date had a much larger effect on the quality of CDC Pacer than AC Assiniboia. Combining early...

The suitability of cool- and warm-season annual cereal species for winter grazing in Saskatchewan.

Winter grazing is a practice that can reduce feeding cost for cattle production. Current production has been utilizing traditional cool-season cereals for winter grazing. Warm season (C4) cereals also have the potential to be adapted to winter grazing in Saskatchewan. The objective of this study was to evaluate cool and warm season annual cereal species for adaptation, quality, and dry matter production in annual fall and winter grazing systems. Two seeding dates, nine treatments and two harvest times were used at sites across Saskatchewan over 3 yr. The crops in this trial have significant differences in maturity and dry matter yield. Seeding date did not consistently affect dry matter yield. Pearl millet [Pennisetum glaucum (L.) R. Br.] and sorghum-sudangrass [Sorghum bicolor (L.) × S. arundinaceum (Desv.) Stapf var. sudanense (Stapf) Hitchc.] had low dry matter yields and were poorly adapted to Saskatchewan. The proso millet (Panicum miliaceum) cultivar, Crown, and the foxtail millet (Setaria italica L...

Early seeding dates improve oat yield and quality in the eastern prairies

Demand for high quality oat (Avena sativa L.) for consumption by humans and race horses has increased, leading to increased oat production on the Canadian prairies. Little information exists on the best management practices for producing high-quality, high-yielding oat using direct seeding systems and cropping practices developed and adopted over the past 15 yr. The objective of this study was to determine the effect of early seeding on grain yield and quality of oat cultivars currently grown in the eastern prairie region. Four seeding dates and four cultivars were tested at Indian Head, Melfort, and Brandon over 3 yr. Moving the seeding date from mid-June to early May increased oat yield, seeds per panicle, kernel weight, test weight and plump seed by 76, 33, 10, 13 and 11%, respectively, when averaged across all locations and years. This increase in yield and quality was probably due to improved environmental conditions and a reduction in crown rust infection (Puccina coronata Corda). Crown rust has a l...

Impact of agronomic factors on seed yield formation and quality in flax

Flaxseed is known to have significant health benefits in human nutrition and when included in animal rations. There is pressing need to improve flaxseed production to meet the growing demand. The objective was to study the effects of three seeding rates (22, 45 and 67 kg ha-1), two seeding dates (early May and late May), three rates of nitrogen (66, 100 and 133% of recommended) and three cultivars (Norlin, AC McDuff and CDC Valour) and at five locations representative of the flax-growing area of the Canadian prairies from 1999 to 2001. The variables of interest were plant density, seed yield and yield formation, seed oil content and oil quality. Plant establishment was always highest with Norlin, but bolls m-2 was similar between the three cultivars. Plant density was always highest with the later plantings. No overall effect of seeding date was observed on grain yield, but the site-year by seeding date interaction showed that the later planting was favoured by the most northerly sites and early planting ...

Rhizobium inoculant and seed-applied fungicide effects on field pea production

Field pea has been shown to benefit from the use of rhizobium inoculation and seed-applied fungicides under intensive production. The objective of this research was to determine the effect of seed- or soil-applied rhizobium (Rhizobium leguminosarum bv. viciae) inoculants and seed-applied fungicides on field pea (Pisum sativum “Carneval”) production on fields with no previous history of the crop. The study was conducted at seven locations in Saskatchewan in each of 2 yr. Fungicide treatments were Apron FL (metalaxyl), Apron FL + Thiram 75WP (dithiocarbamate) and an untreated check in 1997 and a fourth treatment, Thiram 75WP, was added in 1998. Rhizobium treatments were seed-applied liquid inoculant, soil-applied granular inoculant and a non-inoculated check. Inoculation with rhizobium increased nodulation (5 of 10 sites), seed yield (6 of 13 sites), and protein content (3 of 8 sites), but occasionally appeared to reduce emergence (3 of 14 sites). Granular inoculant had more beneficial effects than the liqu...

Management of wild oat (Avena fatua L.) in tame oat (Avena sativa L.) with early seeding dates and high seeding rates

Traditionally, farmers have delayed seeding to manage wild oat (Avena fatua L.) in tame oat (Avena sativa L.) crops, but this practice can adversely affect grain yield and quality. The objectives of this study were: (1) to evaluate the effectiveness of using high seeding rates with early-seeded oat to maintain grain yield and quality, and (2) to determine an optimum seeding rate to manage wild oat and maximize grain yield and quality. The factors of interest were wild oat density (low and high density), seeding date (early May, mid May, early June and mid June), and tame oat seeding rate (150, 250, 350 and 450 viable seeds m-2). The study was conducted at Indian Head and Saskatoon, SK, in 2002, 2003 and 2004, at Winnipeg, MB, in 2002, and at Morden, MB, in 2003 and 2004. Wild oat biomass, wild oat panicle density and wild oat seed in the harvested sample decreased as seeding rate increased, while tame oat biomass and grain yield increased. Wild oat density ranged between 0 and 100 plants m-2 with averages...

Influence of wild oat (Avena fatua) relative time of emergence and density on cultivated oat yield, wild oat seed production, and wild oat contamination

Abstract Wild oat is a serious weed in cultivated oat because there are no herbicides to selectively control it. Considering the effect of time of emergence on weed–crop interference is critical for the development of accurate crop yield loss models and weed density thresholds. Therefore, field experiments were conducted at two locations in Saskatchewan, Canada, in 2002 and 2003 to determine the effect of wild oat density and time of emergence on cultivated oat yield and quality. Wild oat was planted at 50 growing degree day (GDD) intervals ranging from 100 GDD before to 100 GDD after crop planting. Wild oat density ranged from 0 to 320 plants m−2. High densities of early emerging wild oat greatly reduced cultivated oat yield and increased wild oat contamination, with observed oat yield losses as great as 70% and wild oat contamination levels of 15%. Wild oat that emerged before cultivated oat caused considerably more yield and quality loss and had higher reproductive output than wild oat that emerged after cultivated oat. The yield loss caused by individual wild oat plants at low densities (parameter I) ranged from 0.40 to 0.49%. The effect of relative time of wild oat emergence (parameter C) always varied significantly between site-years. However, little variation in absolute values within site-years was observed for cultivated oat yield loss, wild oat seed production, and wild oat contamination, suggesting that relative time of wild oat emergence influences all similarly. The results of this study emphasize both the need to control early emerging wild oat, as well as the importance of time of emergence in the prediction of crop yield loss. Furthermore, our approach of conducting an emergence study based on thermal time is novel and demonstrates a robust, mechanistic method of estimating crop yield losses due to relative time of emergence. Nomenclature: Wild oat, Avena fatua L. AVEFA; oat, Avena sativa L. ‘AC Assiniboia’.