Effects of Agronomic Treatments on Silphium integrifolium, a Potential Perennial Oilseed
A Thesis SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY
Sydney A. Schiffner
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE
Craig C. Sheaffer, Advisor
August 2018
© Sydney Schiffner 2018
Acknowledgements
I would first like to thank my advisor, Dr. Craig Sheaffer, for allowing me to pursue a degree in Applied Plant Sciences on the Agronomy/Agroecology track within his lab. I would next like to thank Dr. Jacob Jungers, and Dr. Nicole Tautges for their assistance with interpreting findings and help with statistical analysis on my data. Next I would like to thank lab technicians Joshua Larson, Lindsay Wilson and Donn Vellekson for their assistance in field management and data collection. Thanks also to the Sustainable
Cropping System/Forages lab and all of the interns and MAST students that helped make my research possible with their dedication to good science and field research. This project was funded by the Malone Foundation through The Land Institute, and I would like to thank Dr. David Van Tassel at The Land Institute for being on call whenever I had any odd question about silphium.
Thank you to my friends and family who have supported me through this rigorous scientific endeavor, and last of all thank you to my fellow graduate students. Without your fellowship for the past few years, I definitely wouldn’t have made it through graduate school, or had as much of a fun time going through it.
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Abstract
Silphium integrifolium (silflower) is a potential perennial oilseed crop that can enhance ecosystem services and provide economic return. The objectives of the first study were to determine the effects of planting density and nitrogen rate on silflower biomass production, seed yield, and seed yield components. The planting density experiment established silflower at five planting densities and at two locations (Becker and St. Paul,
MN) in 2015, and plant measurements were collected in 2016 and 2017. The second experiment tested nitrogen (N) fertilization at five different rates (0, 22, 45, 90, and 179 kg
N ha-1) and two planting densities (11881 and 23762 plants ha-1) at Becker, MN. At Becker in 2016, seed, oil, and biomass yields responded quadratically to planting density, and had an agronomically optimum planting density (AOPD) ranging from 39,000 to 42,857 plants ha-1. Planting density had no effect on yields at Becker in 2017. Planting density had a positive linear effect on biomass production at St. Paul in 2016 and 2017, but no effect on either seed or oil yields in either year. In all locations and years, increased plant density decreased the number of seeds and seed heads produced per plant. Nitrogen had a positive, linear effect on seed, oil and biomass yields in 2016, with no optimum rate within the range tested, but only affected biomass yields in 2017. Planting density and N rate interacted to influence the number of seeds per plant in 2016 and seed mass per seed head in 2016 and
2017. Seed yields averaged 365 kg ha-1 within the planting density study in Saint Paul and
1043 kg ha-1 within the same study in Becker, and reached the largest yields under the highest nitrogen rate and density tested as a part of the nitrogen rate experiment at Becker in 2016. Oil yields ranged from 95 to 218 kg ha-1 on average, and biomass yields ranged from 6.1 to 10.6 Mg ha-1. Relative to annual oilseed crops, seed and oil yields for this new
ii perennial oil species are low, but under optimal production conditions, the potential is seen to be as high as traditional sunflower, and with germplasm improvement, gains should continue.
Both Thinopyrum intermedium (intermediate wheatgrass; IWG) and Silphium integrifolium (whole-leaf rosinweed; silflower) are emerging perennial seed crops that do not produce seed within their establishment year. The second study considered here sought to examine the effects of seeding date on IWG and silflower. To induce flowering in both species, IWG and silflower were sown at multiple dates in the fall into the following spring, to determine the effect of planting date on biomass and seed production, establishment and development. This experiment was performed at one location, St. Paul, MN, for 2015-16 and two locations, St. Paul, MN and Salina, KS, over 2016-17 for IWG. The experiment was performed at St. Paul, MN over 2015-16 and 2016-17 for silflower. The planting dates for each of these species ranged from September 1 2015 to May 1 2016 in the first year’s experiment, then ranged from August 15 2016 to June 1 2017 in the second year’s experiment. Within the silflower experiment, nine different populations were used each year to quantify the effect of selection and seeding date on plant establishment. At the end of each growing season, seed and biomass yields were collected for both species. Height was also collected for IWG, and number of individuals and stage were collected for silflower. Over all years and locations, earlier planting dates resulted in higher biomass and seed yields, and taller heights for IWG at St. Paul, MN. Optimal seeding dates for IWG were determined to be early-October at Salina, KS and mid-August at St. Paul, MN.
Accumulated growing degree days were also examined as a way to predict biomass and seed yields based on seeding date, and each location and year had a similar relationship
iii with growing degree days and the response variables. For silflower in the first year’s experiment, only rows planted in September 2015 produced seed during the following year, indicating some amount of prior growth from the year beforehand being necessary for seed development. However, for 2016-17 these trends were less consistent. September-seeded plots still produced seeds, but a small amount of seed was produced by plants seeded at later dates as well, with plants growing to more intermediate growth stages than were seen in the previous year’s study, reflecting this lack of consistency. Growing degree days was also used as a predictor variable to explain variation of biomass yields and developmental stage in silflower. The second year’s planting did not achieve as many growing degree days as the first year’s, therefore explaining the lack and increased variability in seed and biomass production. However, there may be other considerations to take into account for production of reproductive tissues in silflower than solely accumulated growing degree days such as photoperiod and underground biomass requirements for flowering.
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Table of Contents
Acknowledgements ...... i Abstract ...... ii Table of Contents ...... v List of Tables ...... vi List of Figures ...... vii
Chapter 1. Silphium integrifolium: A Potential Perennial Oilseed and Forage Crop Introduction ...... 2
Chapter 2. Determining Optimum Planting Densities and Nitrogen Rates for the Perennial Oilseed, Silphium integrifolium Introduction ...... 9 Materials and Methods ...... 13 Results ...... 16 Growing Conditions ...... 16 Planting Density ...... 18 Nitrogen Fertilization ...... 19 Discussion ...... 20 Potential of Silflower ...... 20 Effects of Planting Density ...... 22 Effects of N Fertilization...... 24 Yield Components ...... 25 Conclusions ...... 28
Chapter 3. Effects of Seeding Date on Yield and Morphological Characteristics of Thinopyrum intermedium (Intermediate Wheatgrass) and Silphium integrifolium (Silflower) Introduction ...... 39 Materials and Methods ...... 41 Results and Discussion ...... 44 IWG Seeding Date Effect ...... 44 IWG Growing Degree Day Effect ...... 46 Silflower Seeding Date Effect ...... 47 SIL Growing Degree Day Effect ...... 50 Bibliography ...... 61
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List of Tables
Chapter 2 Table 1. Air temperature and rainfall over growing season in 2016 and 2017 in Becker and St. Paul, MN ...... 30 Table 2. ANOVA table displaying linear and quadratic effects of density on seed, and biomass yields and multiple yield-components for silflower in ...... 31 Table 3. Coefficient effects of density on seed, oil and biomass yields and multiple yield components for silflower ...... 32 Table 4. ANOVA table dispalying linear and quadratic effects of nitrogen fertilization rate, and the effect of planting on seed, oil, and biomass yields, and multiple yield components of silflower ...... 35 Table 5. Coefficient effects of nitrogen rate and density on seed, oil and biomass yields and multiple yield components of silflower...... 36
Chapter 3 Table 1. Number of Accumulated Growing Degree Days for seeding dates in St. Paul, MN over 2015-16 and 2016-17 and for Salina, KS over 2016-17...... 53 Table 2. Air temperature and rainfall for 2015-2017 at St. Paul, MN and 2016-2017 for Salina, KS ...... 54 Table 3. Differences between seed and biomass yields, height and number of individuals/tillers for intermediate wheatgrass over different fall and spring seeding dates in 2015-16 and 2016-17 ...... 55 Table 4. Differences between seed and biomass yields, establishment, and stage for silflower over multiple seeding dates and population types from 2015-16 ...... 57 Table 5. Differences between seed and biomass yields, establishment, and stage for silflower over multiple seeding dates and population types from 2016-17 ...... 58
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List of Figures
Chapter 2 Figure 1. Effect of density on silflower seed, oil and biomass yields at Becker in 2016 ..33 Figure 2. Effect of planting density on number of seed heads per plant, and number of seeds per plant at Becker and St. Paul, MN in 2016 and 2017 ...... 34 Figure 3. Nitrogen fertilization and density interaction effects on the number of seed heads and weight of seed per seed head for silflower in St. Paul and Becker, MN over 2016 and 2017 ...... 37
Chapter 3 Figure 1. Effect of accumulated growing degree days on intermediate wheatgrass seed and biomass yields planted in 2015-16 at St. Paul, MN and in 2016-17 at St. Paul, MN and Salina, KS ...... 56 Figure 2. Effect of accumulated growing degree days and population types on biomass yields for silflower planted in the fall and spring of 2015-16 and 2016-17 at St. Paul, MN ...... 59 Figure 3. Effect of accumulated growing degree days and population type on develepmental stage for silflower planted in the fall and spring of 2015-16 and 2016-17 at St. Paul, MN ...... 60
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Chapter 1
Silphium integrifolium: A Potential Perennial Oilseed and Forage Crop
1
Introduction
Annual grain crops dominate the agricultural landscapes of the world. Cereal crops alone were harvested on approximately 720 million hectares around the world in 2014.
About 58 million hectares of those cereal crops were harvested in the United States
(FAOSTAT, 2014). This domination of annual grain crops has detrimental effects on surrounding environments including reduced pollinator habitat, nitrate leaching into waterways, and the excessive greenhouse gas outputs associated with management of annual crops. Annual oilseed crops also make up a significant component of agricultural production on landscape. According to FAOSTAT almost 40 million hectares of United
States farmland was harvested for oilseed in 2014. These oilseeds conventionally grown include soybeans, sunflower, canola, and other minor crops.
Perennial crops occupy approximately 19% of the world’s agricultural land (Cox et al., 2006). These systems consist of orchards and vineyards for fruit production, agroforestry, and grass and legume pasture used for production of animal feed. Systems such as these incorporate many ecosystem benefits compared to annual cropping systems including reduced nitrate leaching, soil carbon sequestration, and reduced soil disturbance
(Pimentel et al., 2013). Perennial crops also take up water and nutrients on cropping landscapes during what otherwise would be periods of fallow in annual systems and decrease other erosional forces through reduced tilling practices and soil cover. However, few of these systems produce grain, oil or cereal crops.
New perennial candidates for grain production have been proposed and examined over the last 10 years by The Land Institute in Salina, Kansas (Cox et al., 2006). Some of these candidates include intermediate wheatgrass (Thinopyrum intermedium), lyme grass
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(Leymus arenarius), and Illinois bundleflower (Desmanthus illinoensis) (Cox et al., 2002).
These potential crops not only evoke the benefits of a perennial system, but they also produce a viable economic product that could supplement our current annual grains.
Along with these perennial cereal grain alternatives, perennial oilseed candidates have been proposed. These plants would produce edible oil as an alternative to annual crop products such as sunflower or canola. Candidates currently under investigation include perennial sunflower (Helianthus annuus x Helianthus tuberosus), Maximillian sunflower
(Helianthus maximiliani) and silflower (Silphium integrifolium; whole-leaf rosinweed).
Maximillian sunflower and silflower have been examined extensively by The Land
Institute, while perennial sunflower has been the focus at the University of Minnesota
(Kantar et al., 2014; Van Tassel et al., 2014).
Silphium integrifolium has recently been the main focus of perennial oilseed research, and demonstrates a high potential for use in cropping systems. Research on this cropping system was started by The Land Institute in 2001, and in 2012, a drought year in
Kansas, seed production for silflower averaged 312 kg ha-1, while annual sunflower failed to produce seed. Research into silflower cropping systems have continued through today at The Land Institute and recently at the University of Minnesota (Van Tassel et al. 2014).
At the University of Minnesota, work has recently been undertaken to understand the physiology, genomics, and breeding potential for the species. Silphium integrifolium is in the family Asteraceae, and has female ray florets and male disk florets, which is the opposite flower composition of sunflower (Van Tassel et al. 2014). The seed has oil content and composition similar to that of undomesticated sunflower (Kowalski and Wierciński,
2004), suggesting there is a large potential for improvement. During the plant’s first year
3 of growth it forms a rosette close to the ground that has an average of 33 leaves each of length 21-47 cm and typically does not produce stems or flower. During the plant’s second year of growth it grows smooth stalks that reach a height of about 184 cm on average, alternately opposite leaves, and develops flowers along the length of the stalk (Kowalski
2004). Although there is potential for the plant to be considered as a perennial oilseed that can provide an economic product, not much is known about the plant’s growth and development, or how it will react to differing agronomic regimes.
S. integrifolium has a range that encompasses Minnesota to Louisiana and extends west to Wyoming and east to Indiana (USDA-NRCS, 2018). Flowers of silflower are a host to many pollinators including honey bees, multiple butterfly species, and even a few beetle species (Bray, 1994; Kowalski, 2008; Graham et al., 2012; Prasifka et al., 2017).
Herbivores such as the white-tailed deer, silphium borer moth, cynipid gall wasp and meadow vole consume either the plant or its seeds (Fay and Hartnett, 1991; Howe and
Brown, 2000; Anderson et al., 2001; Andrew and Leach, 2006). Silflower is relatively drought resistant, as it grows thick roots to capture moisture from approximately 2 m below the surface of the soil (Weaver et al., 1935; Robertson, 1939; Vilela et al., 2018). Silflower provides many ecosystem services, but it is yet unknown how the crop’s growth and physiology changes within a cropping system environment.
A closely related species, S. perfoliatum (cup plant), has been examined throughout
Europe and Asia for its forage potential (Pichard et al., 1997; Clevinger and Panero, 2000;
Jarosław et al., 2007; Liu, 2008; Ruidisch et al., 2015). Cup plant has also been investigated as a form of bioremediation of crude oil residues, cadmium-poisoned soils, and copper mine tailings (Zhang et al., 2006, 2010, 2011). Seed yields for cup plant average around
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587 kg ha-1, and the highest seed yield reported for cup plant was 1265 kg ha-1 (Puia and
Szabó, 1985; Kowalski, 2007). Gansberger et al. (2015) reviewed cup plant studies and found that the species would also be a promising candidate for biogas production. In Asia, an extract from cup plant foliage has even been examined for its use in ice cream and turbid beverages (Qin, 2005; Tan et al., 2005).
The cultivation and proper growing conditions to optimize seed and biomass yield of S. integrifolium have yet to be examined. There is no literature on the proper nitrogen rates, plant population or planting density, and seeding dates for use within silflower cropping systems. Understanding these management variables is important. However, establishment timing appears especially critical, as S. integrifolium doesn’t flower during its first year of growth, and therefore has no potential for economic return in the seeding year. Configuring proper seeding dates could assist in clearing this hurdle.
Nitrogen is often a limiting nutrient to plants, who use it extensively for photosynthesis within the enzyme rubisco, as well as in the generation of amino acids, nucleotides, alkaloids and many other cellular constituents (Brooker et al., 2011).
Therefore, increased nitrogen availability within the soil should lead to increased photosynthetic capability of a non-nitrogen fixing plant. We anticipate that N fertilization of S. integrifolium will affect the amount of biomass and seed production. The amount of
N fertilization given to the plants should also affect their harvest index. In a review of N rate trials performed with S. perfoliatum, N fertilization resulted in increased biomass yield consistently across multiple studies (Gansberger et al. 2015). Although N rate trials examining seed yield have not been performed for silflower, sunflower (Helianthus annuus) trials have shown that adding N to plots can lead to a 40-50% increase in seed
5 production (Helmy and Ramadan, 2008; Sincik et al., 2013), and varying nitrogen rates in cup plant are shown to increase seed yields by a small amount (Shalyuta and Kostitskaya,
2018).
Identifying ideal planting densities and patterns that optimize production is an important facet of agronomic investigation. Pichard (2012) performed density trials with cup plant and found that dry matter yields were not different among plant densities ranging
104,125 to 208,250 plants ha-1. In sunflower, planting densities ranging between 19,530 and 59,940 plants ha-1 produced yields that were highest in the densest plots, however the plants within the highest density plots also produced the least seed per head (Massey,
1971). Planting density trials performed on S. integrifolium will assist in determining the optimum levels of these factors for biomass and seed production.
Determining the appropriate seeding dates for S. integrifolium will assist in identifying ideal dates when seed can be sown for establishment either before winter for overwintering purposes, or in the spring, so as to achieve establishment and grain production. Silphium integrifolium typically flowers from mid-July to early October
(Kowalski 2004). Therefore, the plant sets seed from early August to late October. By mimicking some of the dates that the plant would normally set seed by planting on those dates, one can mimic the seed set of S. integrifolium in native stands. Another reason to examine pre-winter plantings is that the seeds may germinate in the fall, overwinter, and potentially produce flowers during what would normally be their establishment year of growth. Decreasing time to flower for the plant would result in economic return from the crop with less time in the field, making the system more efficient. This experiment is also important in determining whether or not S. integrifolium can be directly seeded with
6 successful survival, and to examine its ability to overwinter in Minnesota. For a wide adoption of the crop, being able to sow directly into the soil with seed, instead of putting in extra time and effort associated with transplants, is critical to modern day farmers.
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Chapter 2
Determining Optimum Planting Densities and Nitrogen Rates for the Perennial Oilseed, Silphium integrifolium
8
Introduction
Annual crop agricultural occupies 90% of farmland in Minnesota (Lofthus and
Byrne, 2016) and has been associated with environmental issues such as fertilizer contamination of waterways, (Randall and Mulla, 2001), pollinator population decline
(vanEngelsdorp and Meixner, 2010), soil erosion, and reduced soil carbon (C) sequestration (Chantigny et al., 1997). The introduction of perennial plants to agricultural landscapes has been proposed as an approach to enhance agricultural sustainability (Glover and Reganold, 2010; Asbjornsen et al., 2013). Perennial grasses and legumes have been shown to provide year round soil coverage, have large root systems, and require less tillage than annual systems (Glover et al., 2010). Thus, perennial systems can reduce soil erosion, increase nutrient retention, and increase C sequestration (Crews and DeHaan, 2015).
Many perennial species found in agricultural systems are grasses and legumes either grown in pastures or harvested for forage (Adler et al., 2009; USDA, 2016). Randall et al. (1997) reported that alfalfa (Medicago sativa) and smooth bromegrass (Bromus inermis) reduced nitrate leaching by 93% and 96% respectively compared to cropping systems under continuous corn production (Zea mays). Soil erosion decreased in systems with Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon dactylon) by up to
99% compared to corn systems (Browning, 1973). Discovering new perennial crops, and developing productive cropping systems around these plants, could promote ecosystem services while providing agricultural products for society.
Oilseeds were grown on 97 million ha of agricultural cropland in the United States in 2015, and had a production value of $37 billion (Ash and Matias, 2018). Soybean
(Glycine max), sunflower (Helianthus annuus), and canola (Brassica napus) dominate the
9 oilseed market in Minnesota. Soybean and sunflower produce linoleic oil, and canola and varieties of high-oleic sunflower produce oleic oils, both of which are components of vegetable oil (Gunstone, 2011). These annual production systems do not cover the soil during spring and fall periods of heavy precipitation and leaching events. Finding alternative oilseeds that are perennial is essential for increasing crop diversity and enhancing multiple ecosystem services to agricultural landscapes.
Silphium integrifolium (common name: whole-leaf rosinweed; silflower) is a perennial prairie forb native to the central region of the United States, ranging from
Colorado to Kentucky and Texas to Minnesota (USDA-NRCS, 2018). It has potential to produce significant biomass, a high quality oil similar to that of soybean (Kowalski and
Wierciński., 2004), and contribute many ecosystem services provided by perennial plants because of its robust growth and penetrating root system (Kowalski, 2004; Vilela et al.,
2018). Silflower also has potential as a source of nectar and pollen for a diverse range of pollinating insect species (Prasifka et al., 2017). Historically, Silphium sp. have been studied as a component of prairies, as well as a source of nectar for insects and seeds for birds (Robertson, 1939; Fay and Hartnett, 1991; Howe and Brown, 2000). In 1999, researchers at The Land Institute in Salina, KS began to select wild candidates and developed crosses to produce a perennial oilseed crop, one of these wild candidates being silflower (Van Tassel et al., 2014; Vilela et al., 2018). Kowalski (2004) examined the production habit of silflower during its first three years of development and concluded the species would be an excellent candidate for forage production. The researchers also examined the potential of cup plant (S. perfoliatum), silflower, and compass plant (S.
10 laciniatum) seed for use as an oilseed, and found that all three demonstrated high potential for oil use within the food industry (Kowalski and Wierciński, 2004).
Agronomic practices for efficient production of S. integrifolium biomass and oil seed production for the United States have not been investigated. Among the essential agronomic practices for consideration are planting density and nitrogen (N) fertilization.
Studies performed throughout Germany have indicated that planting densities of 40,000, to 200,000 plants ha-1 resulted in highest biomass yields for cup plant (Neumerkel and
Martin, 1982; Vetter et al., 2010). This range is defined by two different experiments, where one researcher found that decreased densities lead to increased biomass production and the other study found the opposite to be true. Optimal planting densities for S. integrifolium biomass and seed production are unknown.
Nitrogen fertilization is essential for profitable biomass and seed production of many non-leguminous crops, including annual sunflower (Robinson, 1973). The response of cup plant forage biomass and quality to N fertilizer has been studied mostly in Germany, and to a lesser extent in China, New Zealand and the United States (Shilin et al., 2007;
Šiaudinis et al., 2012). Pichard (2012) found that an application of 100 kg N ha-1 year-1 was sufficient for optimizing cup plant biomass yields in New Zealand. Aurbacher et al. (2012) recommended a fertilization rate of 50 kg N ha-1 in the establishment year, and then a range of 130 – 160 kg ha-1 yr-1 in subsequent years for cup plant production in Germany. These higher rates are similar to those used for optimizing seed yield and oil yields in annual sunflower (Burgland et al., 2007). These results are informative for silflower, however empirical data is needed to make reliable recommendations for cultivation.
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Yield components are individual seed characteristics such as seed weight, length and oil content, that can be influenced by agronomic treatments, and that can influence larger scale plant traits such as oil, seed, and biomass yields. Common yield components for sunflower include seed weight, number of seeds per head, seed head diameter, and seed oil content (Robinson et al., 1982; Gul and Kara, 2015). In sunflower, these traits are heavily influenced by environmental factors, such as planting density, fertilization rate, and environment (de la Vega and Chapman, 2001). These external traits also presumably affect silflower seed yield components. However, some of these physiological characteristics differ between sunflower and silflower. Sunflower only produces a single stem and seed head, while silflower produces multiple seed heads per tiller, and multiple tillers per plant, similar to undomesticated sunflower (Kowalski, 2004). Examining the effects of agronomic treatments on these smaller scale measurements will give an indication of the effects of growing conditions on the single plant level, and then extending to larger scale measurements in silflower.
Planting density and N fertilization are important agronomic factors for increasing biomass and seed production of oilseed crops like cup plant and sunflower, but little to no information is available for silflower. Therefore, our first objective was to determine the most effective planting densities and N fertilization rates for silflower seed, oil and biomass production. Our second objective was to establish how these agronomic field treatments affected seed yield component characteristics of silflower.
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Materials and Methods
Study Sites
Experiments were conducted at two locations in 2016 and 2017, at Becker, MN
(45º23’15”N, 93º53’22”W; Hubbard-Mosford complex [sandy, mixed, frigid Entic and
Typic Hapludolls]) and St. Paul, MN (44º59’44’N, 93º10’13”W; Waukegan silt loam
[Fine-silty over sandy, mixed, superactive, mesic Typic Hapludoll]). Soils at Becker had a pH of 6.6, P of 42 kg ha-1, and K of 110 kg ha-1. At St Paul, soils had a pH of 6.5, P of 215 kg ha-1, and K of 490 kg ha-1. Weather conditions for the two sites during the two site years are shown in Table 1.
Planting Density Trial
The planting density trial was established in 2015 at Becker and St. Paul, MN. The experimental design was a randomized complete block with treatments in a split-plot arrangement in three replications. Whole plots were four distances between plants within a row (0.3, 0.46, 0.61, and 0.91 m) randomly assigned to 3.7 by 6.4 m plots, and two subplot treatments of between-row plant spacings (0.61 and 0.91 m) were randomly assigned within the whole plot treatments. With these configurations, plant density varied from 16 plants per plot (11,881 plants ha-1) for the lowest density planting, to 48 plants per plot
(53,792 plants ha-1) for the highest density planting. In June 2015, silflower seeds from a bulk sample of seed that had undergone four cycles of selection for increased seed yield were germinated and grown in the greenhouse in 50 mm wide x 150 mm tall peat pots for one month. Seedlings had 2 to 3 true leaves and were approximately 15 cm tall when transplanted to the field in early-July 2015. Plots located in Becker were irrigated at a rate of 25.4 mm per week from June to September in 2015, and May to September in 2016 and
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2017. In May 2016 and 2017, plots were fertilized with 67 kg N ha-1 as pelletized urea. In
June 2015, April 2016, and April 2017, all plots were sprayed with Dual II Magnum (a.i.
S-metolacholor 82.4%) at a rate of 2.33 L ha-1 for weed control. Manual weeding was also undertaken as necessary throughout the growing season.
Nitrogen Fertilization Trial
This experiment was established at Becker, MN in 2015 using transplanted seedlings as described in the population density experiment above. The experimental design was a randomized complete block with treatments in a split-plot arrangement and three replications. Whole plots were five N rates randomly assigned to 3.7 by 6.4 m plots.
Two spacing arrangements were assigned to subplots within whole plot N treatment on a density of either 11881 or 26896 plants ha-1, resulting in plots with 16 and 24 plants per plot, respectively. Nitrogen rate treatments included 0, 22, 45, 90, and 179 kg N ha-1, and were applied as pelletized urea in early May of 2016 and 2017. For the plots fertilized with
179 kg N ha-1, the N fertilizer application was split with an application of 89.5 kg N ha-1 in early May and 89.5 kg N ha-1 in early June. Plots were irrigated and weeds controlled as described above for Becker.
Data collection
All response variables were measured on the four innermost plants within each subplot that were representative of the split plot treatments. Seed yields were determined by taking weekly seed head harvests from individual plants over the last week of August through the first week of October in 2016 and 2017. This was done to avoid seed losses to shattering and predation, as well as to collect the highest amount of seed possible from each plant. Seed heads were then bulked, dried at 35˚C, and threshed to determine whole
14 plant seed yields on a dry weight basis. Seed, oil and biomass yields are reported on a per hectare basis. Oil yield was determined by multiplying seed oil content with seed yield.
Seed oil content was determined on a per plant basis with an 8mL sample of cleaned, weighed achenes using nuclear magnetic resonance (NMR) and an Oxford Instruments
MQC benchtop scanner with equations developed by the USDA Sunflower Testing Center in Fargo, North Dakota. Oil concentration is reported on a g kg-1 dry weight and adjusted for a 0% moisture basis.
Number of seed heads per plant was counted while harvesting. Hundred seed count weight was determined by counting 100 seeds per plant, then drying them at 35 ºC and weighing to attain dry matter content. Number of seeds per plant was determined by dividing hundred seed count weight by 100, then dividing total seed yield per plant by the calculated individual seed weight. Weight of seed per seed head was calculated by dividing whole plant seed yield by total number of seed heads. Number of seeds per seed head was calculated by dividing number of seeds per plant by total number of seed heads per plant.
In October of 2016 and 2017, individual plant biomass was harvested to a 6 cm height, weighed wet in the field, and a 300-gram subsample was dried at 60 ˚C and weighed. Yield is expressed on a dry weight basis. Harvest index was calculated by dividing seed yield by whole plant aboveground biomass yield including seed head weight.
Statistical Analysis
Response variables include seed yield, oil yield, biomass yield, seed oil content, harvest index, number of seed heads per plant, number of seeds per plant, weight of seed per seed head, number of seeds per seed head, and hundred seed weight. These variables were measured in both experiments. Linear mixed effects models were generated using the
15 statistical software R and the nlme package to determine the effects of the predictors
(planting density, tiller number ha-1, and nitrogen fertilization rate) on the response variables. Models for the population density experiment included year, location, and the quadratic and main effect of planting density as fixed effects, and replicate, whole plot treatment, and plot as random effects. Location and year interacted to have an effect on every response variable, so the data were analyzed separately by location and year to elucidate the effect of density. Models for the nitrogen rate experiment included year, planting density, and the quadratic and main effect of nitrogen rate as fixed effects, and replicate, whole plot treatment, and plot as random effects. There was an interaction between year and main effects for all response variables, so data were analyzed separately by year.
Model selection followed this initial step, and all interactions that were determined to be significant under Type-I analysis of variance (ANOVA) were retained in the models.
When interactions between main effects were not significant, only the significant main effects were retained in the model. These reduced models were then tested for significant regression effects, and their parameter estimates were calculated. With complex interactions, figures were generated to illustrate the effects of treatments on response variables.
Results
Growing Conditions
Air temperatures were similar between Becker and St. Paul in 2016 and 2017, and differed from the 20-year average over the course of the season for S. integrifolium, which
16 ranged from April to October (Table 1). At Becker in 2016, air temperatures were typically within 1°C of the 20-year average most months, but were 1.2°C higher than the 20-year average in May and in October. In 2017 at Becker, air temperatures in April were 1.6°C higher than the 20-year average, and from May through July were within 1°C of the 20- year average. Air temperatures were 2.1°C less than the 20-year average in August of 2017, but then increased to be within 1°C of the 20-year average in September and October. At
St. Paul in 2016, air temperatures were within 1°C of the 20-year average during the growing season. In 2017, air temperatures were near normal in April, June, and July,
September, and October. Air temperatures at St. Paul in 2017 were 1.7°C and 3.0°C lower in May and August, respectively.
Precipitation at Becker was similar to the 20-year average for April in 2016 and
2017, and was higher than the 20-year average from May to September over the two years of study. At Becker in October, precipitation in 2016 was similar to the 20-year average, and precipitation in 2017 was 92 mm higher than the 20-year average. At Becker, precipitation deficits were compensated for by irrigation with a total of 550 and 575 mm, applied in 2016 and 2017, respectively.
Total rainfall at St. Paul in 2016 was 165 mm higher than the total of the 20-year average. Precipitation was within 50 mm of the 20-year average in April, June, and July, but was 57 mm lower than the 20-year average in May. Rainfall in August and September at St. Paul in 2016 was higher than the 20-year average, 126 mm and 56 mm respectively, while precipitation in October was within 50 mm of the 20-year average. Total rainfall at
St. Paul in 2017 was 91 mm higher than the 20-year average. It was within 50 mm of the
20-year average for April, then 57 mm higher than this average in May. In June of 2017 at
17
St. Paul, precipitation was similar to the 20-year average, and then in July precipitation was
52 mm less than the 20-year average. Rainfall increased in August of 2017 at St. Paul, to be 119 mm higher than the 20-year average, was within 50 mm of the 20-year average in
September, and in October increased to 64 mm higher than the 20-year average for that month and location.
Planting Density
Planting density effects varied by location and year (Table 2). Seed, oil, and biomass yields increased quadratically in response to increased population density at
Becker in 2016, but were not affected by density at the same location in 2017 (Table 2;
Fig. 1). At Becker in 2016, seed yield increased until an agronomically optimum planting density (AOPD) of 39,000 plants ha-1; which produced 1305 kg ha-1 of seed. Oil yield increased until an AOPD of 42,857 plants ha-1, which produced 330 kg ha-1 of oil. In 2016 at Becker, biomass yield increased quadratically until an AOPD of 42,857 plants ha-1, which produced 12.1 Mg ha-1 of biomass. Density did not affect seed or oil yields at St.
Paul in 2016 or 2017, but had a positive linear effect on biomass yield in both years.
Harvest index, the ratio of grain to biomass yield, was not affected by density. Number of tillers per plant was affected by a negative linear effect of density at Becker in 2016 and again at Becker and St. Paul in 2017. Tiller density ha-1 was also examined as a predictor variable for seed and oil yields, had a linear effect on both responses at Becker in 2016 and
St. Paul in 2017, and a quadratic effect on seed and oil yields at Becker in 2017 and St.
Paul in 2016.
The number of seeds and seed heads produced per plant had a negative linear response to planting density at Becker in 2016 and 2017, and at St. Paul in 2017 (Table 2;
18
Fig. 2). Planting density had a quadratic effect on number of seeds produced per plant at
St. Paul in 2016. Seed oil content, weight of seeds per seed head, number of seeds per seed head, and hundred seed weight were not affected by planting density in any of the locations and years considered in this experiment.
Nitrogen Fertilization
Nitrogen fertilization and planting density effects varied between years (Table 4).
Overall productivity was lower in 2017 compared to 2016; therefore, the analysis was conducted separately for each year to determine the effect of N rate. In 2016, N rate had a positive linear effect on seed, oil, and biomass yields as well as harvest index, number of seeds per plant, and hundred seed weight (Table 4; Table 5). At the highest N rate, 179 kg
N ha-1, seed and oil yield reached 1698 and 371 kg ha-1, respectively. Biomass yield increased to 11.2 Mg ha-1 and harvest index rose to 0.17 at the highest N rate in 2016. In
2017, N rate affected fewer variables, seed oil content, biomass yield, number of seeds per plant, and number of seeds per seed head. N rate had a positive linear effect on biomass yield (Table 5) and number of seeds per plant (Fig. 3), and a negative linear effect on seed oil content and number of seeds per seed head. In 2017, biomass yield was highest at 8.86
Mg ha-1 when receiving 179 kg N ha-1, while seed oil content was highest at 213 g kg-1 at a N rate of 0 kg N ha-1.
Planting density within the nitrogen rate experiment had a positive linear effect on seed, oil, and biomass yields and had a negative linear effect on number of seeds and seed heads per plant in 2016 (Table 5). In 2016, at the highest density of 26896 plants ha-1, seed and oil yields were 1320 and 284 kg ha-1, respectively, and biomass yield reached 9.71 Mg
19 ha-1. In 2017, density had a negative linear effect on the number of seeds and seed heads produced per plant (Fig. 3).
Interactions between nitrogen rate and planting density affected number of seed heads per plant in 2016 and weight of seed per seed head in 2016 and 2017 (Table 4). In
2016, at a planting density of 11881 plants ha-1, increasing N rate had a positive linear effect on number of seed heads produced per plant, and at the higher planting density,
26896 plants ha-1, N rate had a quadratic effect on the number of seed heads produced (Fig.
3). Also in 2016, N rate had a quadratic effect on weight of seed per seed head at both densities, with a positive effect at 26896 plants ha-1, and a negative quadratic effect at the lower density, 11881 plants ha-1 (Fig. 3). Nitrogen and density affected seed weight per seed head in 2017 in a similar manner as in 2016, but had lower weights of seed per seed head over all N rate and density treatments.
Discussion
Potential of Silflower
Silflower demonstrated potential as a perennial oilseed in Minnesota, and showed comparable seed and biomass yields to sunflower during its first year of production. Oil yields at within the population density experiment at Becker overall averaged 218 and 95 kg ha-1 in 2016 to 2017, respectively, while at St. Paul, yields were 113 kg ha-1 and 119 kg ha-1 in 2016 and 2017 within the same experiment. At Becker, plants attained higher seed yields in 2016 than in 2017, 1043 kg ha-1 and 411 kg ha-1 on average, respectively.
However, average seed yields increased from 2016 to 2017 in St. Paul, increasing from
365 kg ha-1 in 2016 to 459 kg ha-1 in 2017. A related perennial species, cup plant, has
20 produced 390 kg ha-1 of seed under 120 kg N ha-1 in Belarus (Shalyuta and Kostitskaya,
2018). In comparison, annual sunflower produced 1583 kg ha-1 of oil and 3,814 kg ha-1 of seed at Becker MN (Robinson, 1973, 1985). Another commonly cultivated oilseed species, canola (Brassica napus), produced averages of 1653 kg ha-1 of oil and 3518 kg ha-1 of seed at Roseau, MN in 2017 (Grafstrom et al., 2017).
Seed and oil yield reductions occurred from the first to second year of production at Becker, but did not occur at St. Paul. Potential causes of yield decrease at Becker include an increase in rust infection from 2016 to 2017. In addition, declines in sexual reproductive output are reported to happen in perennial systems such as intermediate wheatgrass
(Thinopyrum intermedium) and other perennial crops (Vico et al., 2016; Jungers et al.,
2017), as over subsequent years of growth, perennial plants devote more energy to underground and structural tissues than sexual reproductive output.
It is apparent that silflower consistently produces half of the oil and 45% less seed than established oilseed cropping systems, such as sunflower. However, with continued selection for traits that increase seed and oil yield, sunflower went from a wild to domesticated species, through 4000 years of development, that now produce 200% larger seeds, 550% heavier seeds, and 54% more oil than its wild progenitors (Burke et al., 2002,
2005). These advancements should continue to be made for silflower as domestication progresses, given that sunflower domestication began with similar types of germplasm and the modern resources we have to characterize and optimize germplasm can allow the process of domestication to much more rapidly (Van Tassel et al., 2017).
Silflower produces comparable biomass to established forage species, but its quality for animal feed has yet to be determined. However, silflower harvested at the end
21 of the growing season likely has low quality forage, as the majority of biomass within the stems is lignified, and this is also seen to occur with alfalfa forage systems when they are allowed to grow for extended periods of time before harvest (Kalu and Fink, 1981).
Biomass production at Becker averaged 7.7 Mg ha-1 and 6.1 Mg ha-1 in 2016 to 2017, respectively, and was similar at St. Paul in 2016, averaging 7.8 Mg ha-1 and higher in St.
Paul in 2017, increasing to 10.6 Mg ha-1. Year to year patterns of biomass yield followed those for seed yield at each location. Albrecht and Goldstein (1997) found that forage yield for cup plant, when produced in Wisconsin, ranged from 9 to 11 kg ha-1, which was comparable to alfalfa biomass yields in similar areas, and 24% higher than silflower biomass yields. Silflower has comparable and even higher biomass yields to other, established, perennial biomass crops. Jungers et al. (2015) reported yields of switchgrass
(Panicum virgatum) and native prairie plants to be 4.7 and 4.5 kg ha-1, respectively, in similar locations. Intermediate wheatgrass, another perennial grass grown for grain as well as forage, has biomass yields of 5.3 kg ha-1 when produced in similar conditions (Frahm et al., 2018).
Effects of Planting Density
For most annual crops, an AOPD has been identified. For example, sunflower has an AOPD of 71,630 plants ha-1 recommended for seed, oil, and biomass production
(Putnam et al., 1990). The range of recommended densities for sunflower typically varies, but individual plants yield less under increased densities, and yields tend to stabilize in terms of seed production when density is increased (Villalobos et al., 1994; Jahangir et al.,
2006). We only found effects of planting density on oil and seed yields for silflower during the first year of seed production at Becker. This lack of response in other years and
22 locations may be a function of all stands reaching a maximum tiller density; of which has not been established for silflower. For perennials that are grown for forage or seed, such as switchgrass, recommended densities exist for maximizing yields (Vogel, 1987); however, often because of extensive crown development and tillering, stem density is a better predictor of biomass and seed yields. Although it is important to note that planting density had a negative effect on number of tillers per plant in silflower, this is seen across many perennial grass systems and tiller density ha-1 is used consistently as a proxy for planting density (Kays and Harper, 1974). It is especially important for this experiment, as inconsistent germplasm was used, meaning all plants behaved differently from one another.
Tiller number per hectare had a positive linear effect on seed and oil yields in 2016 at
Becker, and in 2017 at St. Paul, indicating that these environments did not reach a maximum tiller density, and therefore produced increased seed and oil yields over increasing tiller densities. However, tiller number per hectare had a quadratic effect on seed and oil yields at Becker in 2017 and at St. Paul in 2016, indicating at these environments a maximum tiller density was reached. This is consistent for Becker, as density did not have an effect on yield variables in 2017. In 2016 at St. Paul, however, another cause of yield decline may be due to the incidence of rust (Puccinia silphii) infection inhibiting seed production, as disease prevalence was high at this site, and rust has been identified as a major barrier to wide-scale adaptation of silflower (Turner et la., 2018; Vilela et al., 2018).
Biomass-related traits in silflower were also inconsistently affected by planting density. Harvest index was not affected by planting density at any environment, and that is likely due to the heterogeneous nature of the plant material used for this experiment, as differing cultivars of sunflower are shown to differ in harvest index (Gul and Kara, 2015).
23
Silflower should follow this same trend. At St. Paul in 2016 and 2017, density had a positive linear effect on biomass production, producing 10.3 and 16.5 Mg ha-1 respectively, at the highest densities. In comparison, sunflower produces 12 Mg ha-1 annually and cup plant produces 20 Mg ha-1 and 24 Mg ha-1 during its first and second years of production at similar densities (Villalobos et al., 1994; Vetter et al., 2010). Therefore, silflower, over its first two years of growth, does produce less than cup plant, but produces similar amounts of biomass to sunflower, when grown in St. Paul. At Becker, however, the reverse trend is displayed, indicating that further studies need to examine the plant’s growth and production habits in different environments to establish causes for this lack of consistency in production across different locations and years.
Effects of N Fertilization
The effects of N rate on seed yields, oil yields, and harvest index only occurred in
2016. Since the relationship between these responses and N rate was positive and linear, our recommendation for N fertilization is to apply 179 kg N ha-1 to achieve the highest seed, oil and biomass yields in the first year of seed production. Additional experiments should be performed with higher N rates and over more environments to determine the agronomically optimum N rate for silflower production. The harvest index for silflower has been previously shown to decrease with the application of N (Vilela et al., 2018), but we found the opposite response in the plant’s first year of production. In our experiment, effects of N rate and density were limited to the first year of growth. However, cup plant and sunflower cropping systems both require adequate application of P, K and Mg for optimum biomass and seed production (Burgland et al., 2007; Gansberger et al., 2015), none of which were added to the silflower plots during the years of production. These
24 nutrients may have been depleted over time and could have caused yield reductions over subsequent years of silflower production. Additionally, N was only applied in May and then early June (for the split application), meaning that the plants also did not have access to the nutrient during peak flower production (usually in mid-July to early August).
Fertilizer timing recommendations for sunflower include side-dressing nitrogen when plants are approximately 31 cm tall, and the majority of silflower plots had nitrogen applied before the start of bolting. Optimum N rates for sunflower seed production and cup plant biomass production are reported to be 140 kg N ha-1, and 120 kgN ha-1 respectively
(Burgland et al., 2007; Gansberger et al., 2015). Silflower, when compared to these responses, did not respond to N fertilization as readily during its second year of production, with only biomass increasing with N rate in 2017. However, the plant material used in this experiment was heterogeneous, and with continued selection and more homogeneous plant material, more consistent effects of N on seed, oil and biomass yields should be observed over subsequent production years.
Yield Components
Additional differences include that seed weight for silflower is 66% less than sunflower and oil content is 53.4% lower than domesticated sunflower seeds. Genotype also has a large effect on many of these yield components within sunflower production systems (Gul and Kara, 2015). The effect of genotype on silflower cannot be assessed in these studies since the population is very heterogeneous consisting of diverse genotypes, and no genetic relationship is known between individual plants.
Similar to what is reported for sunflower physiology, planting density had a negative linear effect on some seed yield components of silflower, and no effect on others.
25
Silflower plants produced fewer seed heads at higher densities, and this trend is also observed in head diameter in sunflower (Villalobos et al., 1994). This is a direct result of an increase in competition for above and below ground resources, resulting in reduced seed production, either in the form of fewer seed heads per plant for silflower, or decreased head diameter for sunflower (Burgland et al., 2007). During the first year of production, silflower seed oil content, weight of seeds per seed head, number of seeds per seed head, and hundred seed weight were unaffected by planting density, but this trend occurs within sunflower cropping systems as well, where planting density has an inconsistent effect on yield components (Zubrisky and Zimmerman, 1974). Heterogeneous plant material also contributes to inconsistent effects of density on sunflower seed yield components, and that is likely having an effect on silflower within this experiment (Gul and Kara, 2015).
Seed yield components were influenced by density within the N experiment in the same way as the planting density experiment. Density had a negative effect on number of seeds per seed head and plant in 2016 and 2017. This is similar to the response seen in sunflower; as planting density increases, head diameter and the number of seeds produced per seed head decreases (Jahangir et al., 2006; Andrianasolo et al., 2016). It is possible that this response is similar in silflower, when competition for resources is increased, plants produce less seed heads and therefore less seed overall.
Nitrogen has inconsistent effects on silflower seed yield components over the first and second years of seed production. Number of seeds per plant and hundred seed weight were positively affected by nitrogen in 2016, but not in 2017. Once again, this reinforces the trend that silflower seed yield responses are only influenced by nitrogen fertilization within its first year of growth. Thousand seed weight and number of seeds per plant have
26 a large effect on seed yield within sunflower (r2 = 0.823, p < 0.001 and r2 = 0.763, p <
0.001, respectively) (Marinkovic, 1992), and these trends occur for silflower seed yield as well (r2 = 0.44, p <0.001 for hundred seed weight and r2 = 0.81, p <0.001 for number of seeds per plant).
In 2017, N rate had a negative effect on seed oil content, indicating that increasing nitrogen availability also likely increased protein content in the seed, and decreased oil content, but only in the second year of seed production. This response occurs in annual sunflower in multiple studies, with high rates of N application increasing the amount of protein within seeds, and decreasing oil content by up to 8% in similar locations (Robinson,
1985). Number of seeds per seed head was also affected by a negative linear effect of nitrogen in the second year of seed production, and anecdotally this was due to the effect of rust infection increasing in the plots with higher N fertilization rates. In sunflower cropping systems, plants under high N rates produce higher amounts of biomass, and therefore are more likely to be severely affected by disease and insects, one of the major infections being rust (Muro et al., 2001), silflower seems to follow this trend. Number of seed heads per plant had a positive linear relationship with nitrogen rate in 2017, and this is also reported within sunflower cropping systems, as increasing nitrogen rate leads to an increase in seed production across all planting densities, thus mitigating the reduction effect of increased planting density (Robinson, 1973).
Interactions between nitrogen rate and density only affected two seed yield components, weight of seed per seed head in both years of study, and number of seed heads per plant in 2017. Nitrogen rate increased weight of seed per seed head exponentially in the higher planting density, and increased quadratically in the lower density in 2016. At
27 lower planting densities, sunflower plants have also been observed to produce heavier individual seeds, and therefore higher seed weights per seed head (Robinson, 1985). This trend occurs again in 2017, however to a lesser degree, with plants at both densities producing smaller weight of seeds per seed head than in 2016, another effect of nitrogen having little to no effect on seed yields during the second year of production for silflower.
Number of seeds heads per plant increased with N rate in higher densities, and decreased with increasing N rate in lower densities in the second year of silflower production. Head diameter in sunflower also is affected by the interaction of planting density and nitrogen rate, with plants at lower densities and higher nitrogen rates producing larger heads than plants at higher densities and higher nitrogen rates (Jahangir et al., 2006).
Conclusions
Silflower was examined to determine the optimum planting densities for two years at two locations, and at one location for two years to determine appropriate nitrogen rates. Optimum planting densities during the first year of growth in conditions with sandy soil and irrigated conditions were approximately 40,000 plants ha-1, but density did not have an effect on these responses during the second year of growth. In locations with a high amount fertility, density does not have an effect on production. Number of seed heads and seeds per plant decreased with increasing planting densities. Increasing nitrogen fertilization rates increased seed, oil, and biomass production in the first year of seed production for silflower. However, there was no optimum application found, so the only recommendation that can be given is a yearly application of 179 kg ha-1 to silflower fields. There was no effect of nitrogen fertilization rate on production during the second
28 year of growth, indicating that silflower has a typical perennial growth habit, although the lack of nutrient retention at the experimental location may also play a factor. Seed yield components were inconsistently affected by both nitrogen rate and planting density within the nitrogen rate experiment, but indications of differences in resource allocation given growing conditions occurred. More consistent germplasm should be used in the future when examining the effect of agronomic treatments on silflower growth and production, but this initial work should serve to inform breeders of the plant of conditions to grow the plant in an agronomic setting, as well as future studies into the growth habit of silflower.
29
Table 1. Average monthly cumulative precipitation and temperature during the growing seasons of 2016, 2017 and the twenty-year average (1997 to 2017) at Becker and Saint Paul, MN.
Becker, MN St. Paul, MN Accumulated Rainfall Air Temperature Accumulated Rainfall Air Temperature 20-year 20-year 20-year 20-year Month 2016 2017 2016 2017 Averag 2016 2017 2016 2017 Average Average Average e -----mm------°C------mm------°C--- Apr. 59 81 69 7.3 8.9 7.3 93 93 82 7.7 8.4 8.7 May 95 102 110 15 13.8 13.8 52 166 109 14.8 13.3 15 June 72 106 111 20.2 20 19.3 93 80 124 20.4 20.3 20.3 July 182 37 105 22 22.2 22.3 152 62 114 22.5 22.3 23.1 Aug. 145 119 97 21.1 18.6 20.7 251 226 117 21.5 18.6 21.6 Sept. 119 47 89 16.9 17.5 16.4 132 32 76 17.5 17.6 17.6 Oct. 27 156 64 10 9.3 8.8 84 123 69 10.2 9.5 10 Average/Tota 700 647 645 16.1 15.8 15.5 857 783 692 16.3 15.7 16.6 l § Average temperature and total precipitation over course of growing season.
30
Table 2. Analysis of variance p-values showing the linear and quadratic effects of planting density on response variables collected from the S. integrifolium planting density experiment at Becker and Saint Paul, MN in 2016 and 2017.ǂ Location Year SY OY SOC BY HI SHP SPP WSH SSH HSW Planting
Density Becker 2016 Linear 0.019* 0.021* 0.184 0.052 0.930§ 0.005§** 0.005§** 0.679 0.913 0.294 Quadratic 0.017* 0.016* 0.408 0.036* 0.933§ 0.725§ 0.554§ 0.926 0.653 0.564 2017 Linear 0.412§ 0.276§ 0.628 0.154§ 0.701§ 0.006§** 0.006§** 0.303§ 0.594 0.171 Quadratic 0.077§ 0.133§ 0.882 0.057§ 0.810§ 0.602§ 0.673§ 0.762§ 0.588 0.824 St. Paul 2016 Linear 0.820§ 0.244§ 0.561 0.004** 0.184 0.001§** 4 x 10-4§** 0.240§ 0.740§ 0.457 Quadratic 0.956§ 0.227§ 0.570 0.861 0.408 0.290§ 0.038§* 0.934§ 0.652§ 0.201 2017 Linear 0.506§ 0.839§ 0.184 0.006§** 0.136 0.004§** 0.003§** 0.882 0.899 0.528 Quadratic 0.576§ 0.588§ 0.847 0.762§ 0.444 0.223§ 0.108§ 0.272 0.310 0.247 *,** Significant at the 0.05 and 0.01 probability levels, respectively. § Responses were transformed using a square root transformation to fit model assumptions. ǂ SY, seed yield; OY, oil yield; SOC, seed oil content; BY, biomass yield; HI, harvest index; SHP, number of seed heads per plant; SPP, number of seeds per plant; WSH, seed weight per seed head; SSH, number of seed per seed head; HSW, 100-seed weight.
31
Table 3. Coefficients for linear and quadratic regression models describing the responses that were affected by planting density within the planting density experiment at Becker and St. Paul in 2016 and 2017.
Location Year Response Model# β̂0 β̂1 β̂2 -6 Becker 2016 SYǂ Q -215.8i 0.078 -1 x 10 -4 -9 OY Q 5.30i 6 x 10 -7 x 10 -4 -9 BY Q -0.74i 6 x 10 i -7 x 10 -5 SHP§ L 10.40 -8 x 10 ns -4 SPP§ L 55.2 -4 x 10 ns -5 2017 SHP§ L 8.28 -7 x 10 ns -4 SPP§ L 40.6 -4 x 10 ns -4 St. Paul 2016 BY L 4.90 1 x 10 ns -5 SHP§ L 8.41 -8 x 10 ns -8 SPP§ Q 52.6 -0.001 1 x 10 -5 2017 BY § L 2.45 3 x 10 ns -4 SHP§ L 9.46 -9 x 10 ns -4 SPP§ L 46.5 -5 x 10 ns
§ Reponses were transformed with a square root transformation to fit assumptions of analysis. ns Coefficients were not significant and therefore not included in the models generated. ǂ SY, seed yield; OY, oil yield; BY, biomass yield; SHP, number of seed heads per plant; SPP, number of seeds per plant. # L, linear; Q, quadratic; ns, not significant, α = 0.05. i coefficients were not significant, but were still included in model because of higher-order effects.
32
A B
Figure 1. Effect of planting density on S. integrifolium (A) seed yield and (B) biomass yield within the planting density experiment at Becker, MN in 2016.
33
A
B
Figure 2: Effects of planting density on (A) number of seed heads produced per plant, and (B) number of seeds produced per plant for S. Paul in Minnesota.
34
Table 4. Type I analysis of variance p-values for response variables from the N rate trial in Becker, MN in 2016 and 2017. N rate was analyzed to examine linear and quadratic effects on response variables, then for the linear and quadratic interactions with the main effect of density. Density is also examined as a main effect. Year SYǂ OY SOC BY HI SHP SPP WSH SSH HSW 2016 Nitrogen
Rate Linear 2 x 10-5** 2 x 10-4§** 0.392 0.002§** 0.004** 0.001** 0.001§* 0.032* 0.816§ 0.001** Quadratic 0.308 0.462§ 0.745 0.598§ 0.182 0.586 0.561§ 0.713 0.808§ 0.885 Density 0.004** 0.009§** 0.560 0.001§** 0.582 9 x 10-5** 2 x 10-6§** 0.029* 0.016§* 0.355 Linear 0.655 0.807§ 0.845 0.943§ 1.000 0.017* 0.247§ 0.226 0.202§ 0.289 Quadratic 0.951 0.605§ 0.873 0.398§ 0.141 0.045* 0.211§ 0.012* 0.124§ 0.089 2017 Nitrogen
Rate Linear 0.155§ 0.217§ 0.004** 0.029§* 0.525 0.004§** 0.109§ 0.054 0.018* 0.935 Quadratic 0.232§ 0.529§ 0.619 0.117§ 0.709 0.173§ 0.083§ 0.877 0.622 0.421 Density 0.531§ 0.268§ 0.388 0.437§ 0.621 2 x 10-5§** 4 x 10-4§** 0.580 0.339 0.223 Linear 0.853§ 0.355§ 0.836 0.637§ 0.720 0.113§ 0.824§ 0.512 0.473 0.678 Quadratic 0.211§ 0.142§ 0.311 0.587§ 0.196 0.959§ 0.271§ 0.026* 0.106 0.154 *,** Significant at the 0.05 and 0.01 probability levels, respectively § Responses were transformed using a square root transformation to fit model assumptions ǂ SY, seed yield; OY, oil yield; SOC, seed oil content; BY, biomass yield; HI, harvest index; SHP, number of seed heads per plant; SPP, number of seeds per plant; WSH, seed weight per seed head; SSH, number of seed per seed head; HSW, 100-seed weight.
35
Table 5. Coefficients for regression models describing the responses that were affected by N rate and/or planting density within the N rate experiment at Becker in 2016 and 2017.ǂ
Location Year Response β̂ (Intercept) β̂ (Nitrogen Rate) β̂ (Density) 0 1 3 Becker 2016 SY 528 4.58 0.018
OY§ -4 12.3 0.028 1 x 10 -5 BY § 2.04 0.004 3 x 10 -4 HI 0.131 2 x 10 ns SPP§ 71.4 0.068 -0.001 -5 SSH§ 5.82 ns -3 x 10 HSW 2.00 0.002 ns 2017 SOC 213 -0.121 ns BY § 2.26 0.004 ns SPP§ 49.4 ns -7 x 10-4 SSH 22.1 -0.035 ns
§ Reponses were transformed with a square root transformation to fit assumptions of analysis ns Coefficients were not significant and therefore not included in the models generated. ǂ SY, seed yield; OY, oil yield; SOC, seed oil content; BY, biomass yield; HI, harvest index; SPP, number of seeds per plant; SSH, number of seed per seed head; HSW, 100-seed weight.
36
A Density
B Density
Figure 3: Effect of N rate, planting density, and year on (A) number of seed heads produced per plant and (B) weight of seed produced per seed head for S. integrifolium within the nitrogen rate experiment at Becker, MN in 2016 and 2017.
37
Chapter 3
Effects of Seeding Date on Yield and Morphological Characteristics of Thinopyrum intermedium (Intermediate Wheatgrass) and Silphium integrifolium (Silflower)
38
Introduction
New perennial crops are being developed as a way to provide both ecosystem services and economic returns (Runck et al., 2014). By providing continuous ground cover and extensive root systems, the perennial crops intermediate wheatgrass (Thinopyrum intermedium; IWG), and silflower (Silphium integrifolium; whole-leaf rosinweed, silflower) have potential to provide multiple ecosystem services such as reduced nutrient leaching and runoff, decreased soil erosion, and increased carbon sequestration. IWG reduced nitrate leaching by 86% compared to annual winter wheat when grown in
Michigan (Triticum aestivum L.) (Culman et al., 2013), and produced as much as 960 kg ha-1 of grain during its first year of production in Minnesota (Jungers et al., 2017). Silflower can access soil water down to 2 m and has potential to utilize nitrogen in soil water to prevent leaching (Vilela et al., 2018). Silflower has produced 1700 kg ha-1 of seed and 370 kg ha-1 of oil in Minnesota during its first year of growth (Schiffner et al., in preparation).
Establishment of agronomic management practices is important for the development of IWG and Silflower crops. Among these, identification of appropriate seeding dates for perennial crops is vital to successful establishment of productive stands within a cropping system (White and Horner, 1943; Edwards and Sadler, 1992; Hall, 1995).
This is especially true for perennial systems because stands are maintained for several years following establishment.
Based on our cropping systems in the Midwest, it appears that late- summer and fall are the most probable times for IWG and silflower establishment, since with spring seeding these species will not produce an economic return from grain during the seeding year, and growth would be subject to considerable weed pressure. Late-summer and early-
39 fall seedings of IWG and silphium in Minnesota would also provide the opportunity for economic return from a spring seeded grain crop harvested before early August. While optimum dates of summer and fall seeding have not been determined for IWG and silflower, previous work with forage legumes such as alfalfa (Medicago sativa) and perennial grasses has shown that seeding should occur about six weeks before the average date of the first killing frost (Hall and Collins, 2018). This planting date typically results in plants with 4-6 true leaves and an adequate root and crown system to avoid the risk of winter injury (Arakeri and Schmidt, 1949; Sheaffer et al., 2003). For other cool season grasses, typically 3-4 four leaves are required for winter survival (White and Horner, 1943).
Delayed plantings can result in stand mortality and subsequent reductions in biomass yields the year following seeding (Hall, 1995). Intermediate wheat grass has been successfully established using summer, spring and fall seedings (Jungers et al., 2017), but the effect of alternative seeding dates on establishment and grain yields during the establishment year is unknown.
Intermediate wheatgrass requires vernalization to flower, therefore spring planted stands grow vegetatively and have not been observed to flower in the seeding year
(Frischknecht, 1951; Kowalski, 2004). Ivancic and Picasso (2017) reported that IWG flowering was best induced by a 4 °C temperature and 10-hour photoperiod. Therefore, fall planting dates are also critical because IWG needs sufficient morphological development to experience temperature (vernalization) and flowering induction for spring flowering.
(Heide, 1994; McDonald et al., 1996). Ketellapper (1960) determined in preliminary experiments that Phalaris tuberosa (koleagrass) can be successfully vernalized when plants have three leaves. However, the exact level of morphological development or leaf
40 number for IWG or silphium required for inducement is unknown. Our objective was to determine the effect of late-summer, fall and spring seeding dates on IWG and silflower morphological development and seed production.
Materials and Methods
Study Sites
Seeding date studies were conducted in 2015-2016 and 2016-2017 at St. Paul, MN and in 2016-2017 at Salina, KS. The soil at St. Paul, MN (44º59’44”N, 93º10’13”W) was a Waukegan silt loam [Fine-silty over sandy, mixed, superactive, mesic Typic Hapludoll] with a pH of 6.5, P of 215 kg ha-1, and K of 490 kg ha-1. The soil at Salina, KS (38°46’13”N,
97°34’6”W) was a Hord silt loam [fine-silty, mixed, superactive, mesic Cumulic
Haplustoll] and Cozad silt loam [coarse-silty, mixed, superactive, mesic Typic Haplustoll]) with a pH of 7.3, P of 84 kg ha-1 and K of 629 kg ha-1. Cumulative growing degree days by date for all site-years are shown in Table 1, and are calculated based on a base temperature of 0°C for IWG (Frank, 1996) and 6.7°C for silflower (Kandel, 1995) after five days of consecutive growth. Weather data for all years of study is shown in Table 2.
Experimental Layout
Two experiments were conducted, one using IWG and the other using silflower.
For the IWG experiment, the experimental design was a randomized complete block with four replications. Treatments for the 2015-2016 IWG study were 6 seeding dates. The
2016-2017 experiment included 10 seeding dates at St. Paul, MN, and 9 seeding dates at
Salina, KS (Table 1). The 2015-2016 and 2016-17 IWG experiments were seeded at a rate of 6 and 7.1 kg seed ha-1, respectively. One IWG germplasm (TLI-C4) from a single seed
41 lot was used across all experiments, locations, and years of study. TLI-C4 is a breeding population developed at The Land Institute in Salina, KS from four cycles of selection for yield per head, threshability, early maturity and seed size (DeHaan et al., 2018). Treatments were randomly assigned to one-row plots, each 5.5-m long with 0.9 m between rows. Plots were fertilized with 67 kg ha-1 of N as pelletized urea in May of each year following fall seeding. Manual weed control occurred as necessary.
The silflower experiment was similar to that of IWG, except the experimental layout was a randomized complete block with a split-plot arrangement, where the whole plot factor was individual rows as seeding dates (Table 1) and the split plot treatment included 9 varieties (1048, 1093, 1158, 1252, 1327, 1592, 1950, S13.5, and S13.39 in 2016) selected at the Land Institute, Salina, KS. Varieties 1048, 1093, 1158, 1252, 1327, 1592, and 1950 were selected for increased ligule number, S13.5 was collected from wild S. integrifolium plants in KS, and S13.39 was from S. integrifolium var. integrifolium. For the
2016-2017 silflower seeding date study new populations were used as the split plot factor
(S13.5, S13.39, ZRX1, ZS31, ZS91, ZSE1, ZSK1, ZSP1, and ZT31). Populations ZRX1,
ZS31, ZS91, ZSE1, ZSK1, ZSP1, and ZT31 were populations selected for increased ligule number, and S13.5 and S13.39 were the same populations used in the previous year. Each population/seeding data treatment was seeded in a one-row plot 1.5 m long at a rate of 20 seeds m-1 with 0.9 m between rows. In May 2016 and 2017, plots were fertilized with 67 kg ha-1 of N as pelletized urea. Manual weed control was undertaken as necessary throughout both growing seasons and experiments.
Data Collection
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For the IWG seeding date experiments, biomass and seed yields were collected from three, 0.3 m sections of each plot when grain reached maturity (13 August 2016 and
2017 at St. Paul, MN and 20 July 2017 at Salina, KS). Height was measured from the tallest individual in the center section of each row.
For the silflower seeding date experiments, plant counts were conducted each year in June in the year after seeding. Biomass and seed yields were harvested from the entire
1.5 m row on 16 October in 2016 and 12 October in 2017. Developmental stage of the most mature individuals was determined for all populations at seed harvest. The key used for staging ranges from 0 to 8, and specifies growth stages as follows; 0 = cotyledon and true leaf formation 1 = full rosette, 2 = bolting, 3 = bud production, 4 = female floret production,
5 = anthesis, 6 = loss of male and female florets, 7 = seed development, 8 = seed maturity.
Statistical Analysis
Analyses were performed using the statistical software R and the nlme package to examine the effects of seeding date on seed and biomass yields and plant height response variables for IWG. Seeding date was considered as the only fixed effect in these models, and replicate was considered as a random effect. Because seeding dates varied by year, each location/year combination was analyzed independently. For the IWG seeding date experiment, least squared means were compared using Tukey’s adjusted P-value of 0.05 to examine the differences in response variables between seeding dates. A regression analysis was then performed to examine the effect of cumulative growing degree days on biomass and seed yields. Models tested the effect of growing degree days as quadratic and linear fixed effects, and replicate and seeding date as random effects. These models were assessed using Type-I analysis of variance (ANOVA) and coefficients deemed non-significant were
43 discarded from the model. New models were then constructed of only significant terms, and their lower-order counterparts.
The effect of seeding date and population group on silflower seed and biomass yields, number of individuals and developmental stage was analyzed using linear mixed effects models in R. Population groups designated as S13.5 and S13.39 were identified as
‘Wild’ and all other populations were identified as ‘Selected’. Population group and seeding date were tested as fixed effects, and replicate and seeding date were considered random effects. The experiment-years were analyzed separately to avoid conflict with differing seeding dates and populations. To examine the effect of growing degree days on biomass and seed yields, number of individuals, and developmental stage, a regression analysis was performed using R and the nlme package. Within the regression model, the linear and quadratic effect of growing degree days, as well the interaction and additive effect of population group, were considered as fixed effects. Random effects included replicate, population and seeding date. Model selection was then performed using Type-I analysis of variance (ANOVA), and all terms deemed non-significant at an α = 0.05 level were discarded from the model, unless higher-order terms that contained the factors were significant.
Results and Discussion
IWG Seeding Date Effect
IWG seed yields, biomass yields, and plant heights were greatest when seeded at the earliest date in the year prior to harvest (Table 3). In both years at St. Paul, planting
IWG in the late summer (August to September) resulted in seed production in the following
44 year, while planting after October resulted in minimal or no seed production the following year. In Salina, KS seed yields were high when IWG was planted from September through
October, and decreased thereafter. There is little information on seeding date effects for grain-producing IWG, but Frischknecht (1951), working with a forage type IWG in Central
Utah, observed that only IWG planted in the fall produced seed the following year. Pfender
(2004), in Oregon, showed that early November seeding dates resulted in reduced perennial ryegrass (Lolium perenne L.) seed yields when compared to early-September planting dates. The lack of seed production in our study from winter and spring seeding dates across diverse latitudes indicate that IWG has a vernalization requirement for seed production, reinforcing past studies with similar findings (Frischknecht, 1959).
Biomass yields of IWG in the summer followed a similar trend to seed yields across all locations and years, except for the fact that spring dates also produced biomass. At St.
Paul in 2015-16, biomass yields were greatest for both September and October 2015 seeding dates and declined with subsequent seeding dates. Likewise, for the 2016-17 planting at St. Paul, biomass yields were greatest for the August seeding date before declining. Biomass yields from the August planting were almost two times greater compared to planting only two weeks later, in early September. Planting from December onward was largely a failure, as there was poor establishment, and therefore reduced biomass production. In Salina, KS, planting September 15th through October 15th produced the most biomass, with earlier and later fall planting dates producing reduced amounts. As occurred at St. Paul, the trend of decreasing biomass from fall to spring occurred at Salina, with plots producing much less biomass when planted in the spring versus plantings in the early- and late-fall. Differences in biomass production across all locations and years from
45 fall to spring plantings are likely due to the additional mass being produced in reproductive structures of fall-seeded plots.
Height of IWG followed the same trend as biomass yield, the earliest plantings with the highest biomass yield were consistently among those with the tallest IWG plants.
Pearson correlation coefficients between biomass and height were very high for each experiment and year (St. Paul, MN 2015-16, r = 0.87, P = <0.001; St. Paul, MN 2016-17, r = 0.75, P = <0.001; Salina, KS 2016-17, r = 0.91, P= <0.001), indicating that plant height is an adequate indicator of biomass yield for IWG.
IWG Growing Degree Day Effect
Cumulative growing degree days (GDD) between planting and harvest was positively associated with seed yield and biomass production in IWG across all locations and years (Fig. 1). The relationship between GDD and seed and biomass yields at St. Paul,
MN was linear for the 2015-16 and 2016-17 experiments. In Salina, KS the relationship between GDD and seed and biomass yields was linear. At. St. Paul, number of plants at harvest responded quadratically to growing degree days in 2015-16 while number of tillers had a linear response to growing degree days in 2016-17 (Fig. 1).
Relationships between growing degree days accumulated in fall and forage crop yields have also been observed by Hall (1995) in Pennsylvania. He found that delaying planting until after early August decreased plant height and percent cover of multiple cool- season and legume forage species, resulting in reduced stands that could not compete well against weeds or produce adequate forage yields during the subsequent year of establishment. Kilcher (1961) also performed a similar experiment with many cool-season grasses and concluded that a forage type intermediate wheatgrass produced in
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Saskatchewan should be seeded in the spring, as the plants were not tolerant enough to survive the harsh winters in southern Canada. Since conditions in St. Paul, MN and Salina,
KS are more favorable for fall growth and winter survival, these recommendations are different for these locations.
Effects of growing degree days on cool-season perennial grasses are relatively consistent across multiple species, and fall planting provides more benefits than solely seed yield in the subsequent year of production (Hall, 1995). Similar effects of growing degree days on individual seed and biomass yields are observed in IWG (Jungers et al., 2018) as well as other perennial, cool-season grassland systems, with perennial ryegrass ground cover increasing over growing degree days in turf grass (Valverde and Minner, 2008) and agricultural production systems (Hall, 1995; Reicher et al., 2000; Undersander and Greub,
2007). Overall, recommended seeding dates for IWG, based on this experiment, are mid-
August for St. Paul, MN and early-October for Salina, KS. Planting IWG at these dates will cause the plants to achieve relatively high seed and biomass yields at harvest, that are comparable to those found in subsequent years of production (Jungers et al., 2017), and tall plants with sufficient land cover in the form of multiple individuals and tillers that will enable the plants to compete against weeds during the establishment year. Fall plantings will also assist in taking up additional water and nitrate that would otherwise be removed out of agricultural systems during spring snow melts, thus decreasing nitrate leaching to vulnerable waterways (Culman et al., 2013).
Silflower Seeding Date Effect
For the 2015-16 experiment, only plants sown in September yielded seed, and seed yields were similar between the wild and selected groups when averaged over all seeding
47 dates (Table 4). Neither seed yield nor biomass yield differed between two wild populations and among the seven selected populations each year (P > 0.05). Therefore, for simplicity of presentation, mean results of these populations are presented. In 2016-17 average seed production was much less than occurred in 2015-2016, but again most seed was produced at the 4 September seeding date (Table 5). The selected population group produced a small amount of seed when sown in November, December and April. The contrast in seed production between years may have been caused by differences in weather
(Table 2), as the longer, warmer winter of 2016-17 may have disrupted normal vernalization processes. However, it may also be the case that silflower doesn’t have a strong vernalization requirement to flower, as plants have been observed to begin to bolt without undergoing a months long cold period (D.L. Van Tassel, personal communication,
2016).
Biomass was produced from all planting dates in 2015 and 2016, but the trends in production differed. In 2015-16, production was greatest for the September seeding date but similar or less for the other dates. In 2016-17, September through November plantings all had similar biomass production with smaller amounts resulting from March through
June. During the spring of 2017, precipitation was higher than in 2016, this may have allowed more biomass to accumulate in April seeded plants, and therefore enough underground biomass to develop to allow for stem and flower production. Wild and selected populations had similar average seed yields each year with biomass yield greater for the selected group in 2015-2016 while it was greater for the wild populations in 2016-
2017. Differences in responses over establishment years may be related to weather conditions. The air temperatures were higher in 2016-17 than 2016-15, which may have
48 limited vernalization. However, silflower is known to have moderate seed yields when produced in Kansas, where the average winter temperature is higher than Minnesota, so this limited vernalization is unlikely (Vilela et al., 2018). Maturity may have also been delayed by the cooler late summer temperatures in August 2017, resulting in reduced development.
The establishment of plants in 2015 and 2016 were affected by seeding date in different ways. In 2015-16, plants established at all planting dates. The October and
November planting dates had population groups that had the lowest establishment compared to the other seeding dates. This may be due to some plants germinating in the fall before the frost, but not developing enough biomass belowground to survive the winter conditions, and therefore most likely perishing over the winter. December plantings did not follow this trend, as seed was sown into cool soil and weather conditions (under a base growing temperature of 6.7°C) that did not allow for germination until the subsequent spring. In 2016-17, the number of individuals were similar for most fall and early spring dates, but least for the June seeding date, and highest for the November seeding date.
As indicative of the seed yield data in 2015-16, plants achieved the highest development stage when seeded in September, with the majority of populations planted at this date reaching close to seed maturity (stage = 7.0 – 8.0). Populations seeded from
November to May did not produce flowers and were at a vegetative rosette stage. Plants were overall less mature in 2017 than in 2016. This likely reflects the lower seed yields than in the previous year. In contrast to 2016, there was similar development for the
September to December planting dates; however, plants sown on the May and June seeding dates were again the least developed. The wild population group was somewhat less mature
49 than the selected group in 2015-2016 but the two populations had similar average maturity in 2016.
Pearson correlation coefficients for developmental stage with seed yield was moderate in 2015-16 (r = 0.5, p = <0.001), likely due to the fact that seed yields were only obtained in the September seedings, and were zero for all other dates. However, correlation was decreased for the 2016-17 experiment (r = 0.22, p = <0.001), due to the decrease in seed production in the second year, as well as the decreased overall stage at the end of the year for all plants. Stage and biomass yields were correlated in both years of study (2015-
16: r = 0.76, p = <0.001; 2016-17: r = 0.62, p = <0.001) as developmental stage was more indicative of biomass yields than seed yields. Biomass yields are much more likely to reflect developmental stage than seed yields, as the presence of a budding stem or rosette is correlated much higher with biomass, than by the presence or absence of seed.
SIL Growing Degree Day Effect
Biomass yield responded quadratically to GDD in both 2015-16 and 2016-2017.
During the 2015-16 seeding date experiment, GDD and population type influenced biomass production, separately. For the 2016-17 experiment, GDD and population type interacted to affect biomass production together (Fig. 2). Although the responses varied over years, this indicates the importance of GDD in affecting plant development. For the
2015-16 experiment, there’s a clear trend of low biomass for the range of 2002 – 2286
GDD, while rows that achieved 2591 GDD produced reproductive structures, and therefore had much more additional biomass than the other planting dates. This trend is less consistent in the 2016-17 experiment, as there are larger ranges associated with biomass production within the groups, and the trends are quite different from those seen in 2015-
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16. Additionally, the 2016-17 experiment did not undergo as many GDD as the 2015-16 experiment, and this one of is the likely causes of the difference in biomass production.
Growing degree days also had a quadratic effect on developmental stage in 2015-
16, and in 2016-17 (Fig. 3). In the 2015-16 experiment GDD and population group had an effect on developmental stage. During the 2016-17 experiment, only GDD had an effect on developmental stage for both groups. Harvest occurred at similar dates between the two years, but the 2016-17 experiment experienced reduced accumulated growing degree days, which may explain why, on average, the stage for both population groups was 4, which is shortly after budding and approximately 250 GDD short of seed production, when compared to the 2015-16 experiment.
Based on these results, silflower should be seeded as early as possible in September in Minnesota. Depending on soil moisture and weather conditions, seeds will germinate and seedlings will persist throughout the winter. Winter vernalization will occur within the plants to produce some seed the following year. However, first-year yields after fall seeding will be much less than typical second-year yields (92% less), and vernalization requirements for silflower are still uncertain. In 2015-2016, our data suggest that vernalization is important for obtaining first-year seed yield. However, data from 2016-
2017 suggest the opposite. This is somewhat consistent with what has been observed in the field, typically at least a few plants tend to bolt during their first year of growth without undergoing an extended cold period. Some populations of silflower may be day-neutral or have another mechanism for flowering outside of vernalization, as there is a large variation for photoperiod response in perennial species in the genus Helianthus, which is also within the Asteraceae family with silflower (Henry et al., 2014). For restoration of prairies, fall,
51 spring or dormant seeding is recommended, but all seedings depend on soil moisture, air temperature, and planting conditions (Wilson, 2002; Williams, 2010). From field observations, biomass production was higher for vernalized plants than non-vernalized plants. Even if vernalization did not result in plants bolting during the next year after seeding, the process did result in plants producing larger rosettes than spring silflower seedings. Belowground biomass limitations could influence the production of reproductive structures in silflower, which has been observed in annual versus perennial sunflower systems (Gaines et al., 1974). Therefore, fall seeding of silflower will likely provide seed the next spring, or at least larger rosettes that can increase ground cover and shade out competing weeds at the ground level. However, the success of stands depends on the population being used, site conditions at planting, and the winter conditions leading up to spring.
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Table 1: Growing degree days calculated for IWG (left) based on a base temperature of 0°C and silflower (right) based on a base temperature of 5°C for seeding dates in 2015-2017. Seeding date treatments for all experiments are also displayed. IWG SILFLOWER St. Paul, MN Salina, KS St. Paul, MN 2015-16 2016-17 2016-17 2015-16 2016-17 Date GDD Date GDD Date GDD Date GDD Date GDD 1 Sept. 2015 3308 18 Aug. 2016 3646 6 Sept. 2016 4564 1 Sept. 2015 2591 4 Sept. 2016 2346 1 Oct. 2015 2796 1 Sept. 2016 3374 15 Sept. 2016 4378 1 Oct. 2015 2286 1 Oct. 2016 2080 15 Dec. 2015 2290 15 Sept. 2016 3115 29 Sept. 2016 4082 1 Nov. 2015 2120 2 Nov. 2016 1979 21 Mar 2016 2290 1 Oct 2016 2861 13 Oct. 2016 3848 15 Dec. 2015 2120 1 Dec. 2016 1902 1 Apr 2016 2166 15 Oct. 2016 2709 1 Nov. 2016 3519 1 Apr. 2016 2074 22 Mar. 2017 1902 1 May 2016 1906 1 Nov. 2016 2567 17 Nov. 2016 3345 1 May 2016 2002 1 Apr. 2017 1902 17 Nov. 2016 2424 15 Feb. 2017 3012 4 May 2017 1835 1 Dec 2016 2417 16 Mar. 2017 2756 1 June 2017 1594 1 Apr. 2017 2274 13 Apr. 2017 2392 4 May 2017 1984
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Table 2: Monthly average temperature and accumulated precipitation in St. Paul, MN from 2015 through 2017, and 2016-2017 for Salina, KS. Averaged data over 20 years is also included as a comparison. X = Row with average temperature and accumulated precipitation over year.
St. Paul, MN Salina, KS Accumulated Rainfall Air Temperature Accumulated Rainfall Air Temperature 20-year 20-year 20-year 20-year Month 2015 2016 2017 Average 2015 2016 2017 Average 2016 2017 Average 2016 2017 Average -----mm------°C------mm------°C--- Jan. 7 7 24 16 -8.6 -9.6 -7.5 -8.8 18 51 21 0.8 3.2 -0.3 Feb. 6 20 18 20 -12.8 -5.5 -2.3 -6.3 13 2 27 5.8 7.0 2.1 Mar. 18 55 15 41 -0.1 3.5 -0.7 0.4 18 92 45 10.8 10.2 7.8 Apr. 53 93 93 82 8.5 7.7 8.4 8.7 111 93 64 14.7 14.3 13.0 May 125 52 166 109 13.8 14.8 13.3 15.0 140 98 110 18.0 18.8 18.8 June 84 93 80 124 19.8 20.4 20.3 20.3 11 43 99 27.3 26.2 24.8 July 157 152 62 114 21.9 22.5 22.3 23.1 59 43 90 28.7 29.3 27.6 Aug. 71 251 226 117 20.1 21.5 18.6 21.6 199 28 87 26.5 24.7 26.4 Sept. 97 132 32 76 18.8 17.5 17.6 17.6 30 46 66 22.8 23.9 21.5 Oct. 73 84 123 69 9.8 10.2 9.5 10.0 58 147 46 17.4 15.3 14.4 Nov. 116 69 11 33 4.3 5.8 -0.6 2.2 15 2 28 10.7 8.6 7.1 Dec. 54 51 16 27 -2.1 -7.0 -8.3 -5.9 22 1 24 -0.2 1.4 0.6 Average/ 861 1058 865 830 7.8 8.5 7.6 8.1 695 646 708 15.3 15.2 13.6 Totalx
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Table 3: Effect of planting date on IWG seed and biomass yields at grain maturity, and height.
Seed Yield Dry Biomass Height Planting Date (kg/ha) (kg/ha) (cm) St. Paul, MN 2015-16 1 Sept. 2015 839 b§ 6925 b§ 152.0 c 1 Oct. 2015 497 b 5239 b 112.8 b 15 Dec. 2015 5 a 1069 a 58.5 a 21 Mar 2016 0 a 802 a 31.8 a 1 Apr 2016 0 a 910 a 33.0 a 1 May 2016 0 a 689 a 25.8 a St. Paul, MN 2016-17 18 Aug. 2016 898 c§ 10384 dǂ 148.0 d 1 Sept. 2016 588 bc 5706 c 126.3 cd 15 Sept. 2016 443 b 5690 c 130.3 cd 1 Oct 2016 460 b 5271 c 124.0 cd 15 Oct. 2016 346 b 4592 c 124.3 cd 1 Nov. 2016 58 a 1485 b 116.5 cd 17 Nov. 2016 44 a 1305 b 108.5 c 1 Dec 2016 5 a 158 a 0.0 a 1 Apr. 2017 0 a 1520 b 49.5 b 4 May 2017 0 a 289 ab 35.0 b Salina, KS 2016-17 6 Sept. 2016 1110 bc 11193 cd 135.0 cd 15 Sept. 2016 1259 c 13776 de 137.5 cd 29 Sept. 2016 1349 c 14063 e 143.8 d 13 Oct. 2016 1195 bc 12556 de 136.3 cd 1 Nov. 2016 927 b 8969 c 127.5 c 17 Nov. 2016 289 a 5094 b 113.8 b 15 Feb. 2017 0 a 2081 a 36.3 a 16 Mar. 2017 0 a 2511 ab 35.0 a 13 Apr. 2017 0 a 1076 a 26.3 a
Letters signify differences between treatments within year and location using a least- squares means procedure and α = 0.05. § Response was transformed using a logarithm of the response +1 to fit model assumptions. ǂ Response was transformed using a square root to fit model assumptions.
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Year and Location
Figure 1: Effect of growing degree days on IWG seed and biomass yields when fall and spring planting over 2015-16 at St. Paul, MN and 2016-17 in St. Paul, MN and Salina, KS.
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Table 4: Effect of planting date from September 2015 to May 2016 on silflower seed and biomass yields, number of individuals, and developmental stage at silflower harvest in 2016. Numbers shown are group means of treatments over one study featuring different population groups. Population Selected Wild Mean Planting Date Seed Yield§ 1 Sept. 2015 117.7 38.8 78.3 b 1 Oct. 2015 0.0 0.0 0.0 a 1 Nov. 2015 0.0 0.0 0.0 a 15 Dec. 2015 0.0 0.0 0.0 a 1 Apr. 2016 0.0 0.0 0.0 a 1 May 2016 0.0 0.0 0.0 a Mean 19.6 6.5 Biomass Yieldǂ 1 Sept. 2015 1888 1492 1690 b 1 Oct. 2015 266 101 183 a 1 Nov. 2015 202 14 108 a 15 Dec. 2015 190 86 138 a 1 Apr. 2016 168 167 167 a 1 May 2016 129 278 204 a Mean 474 b 356 a Number of Individuals 1 Sept. 2015 8 5 6 b 1 Oct. 2015 6 2 4 ab 1 Nov. 2015 4 1 2 a 15 Dec. 2015 8 1 5 b 1 Apr. 2016 7 2 4 b 1 May 2016 6 4 5 b Mean 6 b 2 a Developmental Stageǂ 1 Sept. 2015 6.9 6.6 6.8 c 1 Oct. 2015 3.0 1.8 2.4 b 1 Nov. 2015 2.0 0.3 1.2 a 15 Dec. 2015 1.7 1.3 1.5 ab 1 Apr. 2016 1.7 2.2 2.0 b 1 May 2016 1.4 1.6 1.5 ab Mean 2.8 b 2.3 a Letters signify differences between seeding dates and populations using a least-squares means procedure on transformed responses using α = 0.05. Absence of letters indicates no difference between mean values. § Response was transformed using a logarithm of the response +1 to fit model assumptions. ǂ Response was transformed using a square root to fit model assumptions. Developmental Stage Key: (0 = cotyledon and true leaf formation, 1 = rosette, 2 = bolting, 3 = bud production, 4 = female floret production, 5 = anthesis, 6 = loss of male and female florets, 7 = seed development, 8 = seed maturity)
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Table 5: Effect of planting date from September 2016 to June 2017 on silflower end-of-season seed and biomass yields, number of individuals and developmental stage at silflower harvest in 2016. Numbers shown are group means of treatments over one year of study featuring different population groups. Population Planting Date Selected Wild Mean Seed Yield§ 4 Sept. 2016 3.9 30.5 17.2 b 1 Oct. 2016 0.6 0.0 0.3 ab 2 Nov. 2016 0.5 0.4 0.4 ab 1 Dec. 2016 0.1 0.2 0.1 a 22 Mar. 2017 0.0 0.0 0.0 a 1 Apr. 2017 0.1 0.0 0.1 a 4 May 2017 0.0 0.0 0.0 a 1 June 2017 0.0 0.0 0.0 a Mean 0.6 3.9 Biomass Yieldǂ 4 Sept. 2016 645 1813 1229 cd 1 Oct. 2016 529 1201 865 bcd 2 Nov. 2016 947 1372 1159 d 1 Dec. 2016 743 900 822 bcd 22 Mar. 2017 413 697 555 bc 1 Apr. 2017 537 576 556 bcd 4 May 2017 350 458 404 b 1 June 2017 85 138 112 a Mean 531 a 894 b Number of Individuals 4 Sept. 2016 8 9 8 cd 1 Oct. 2016 8 9 9 cd 2 Nov. 2016 10 12 11 d 1 Dec. 2016 7 6 7 bc 22 Mar. 2017 6 5 5 b 1 Apr. 2017 7 7 7 bc 4 May 2017 6 4 5 ab 1 June 2017 3 3 3 a Mean 7 7 Developmental Stageǂ 4 Sept. 2016 3.6 3.2 3.4 cd 1 Oct. 2016 2.6 3.0 2.8 bcd 2 Nov. 2016 4.2 4.3 4.3 d 1 Dec. 2016 3.1 2.9 3.0 cd 22 Mar. 2017 2.2 0.9 1.5 abc 1 Apr. 2017 2.3 1.5 1.9 bc 4 May 2017 1.3 1.0 1.2 ab 1 June 2017 0.8 0.9 0.8 a Mean 2.5 2.2 Letters signify differences between seeding dates and populations using a least-squares means procedure on transformed responses using α = 0.05. Absence of letters indicates no difference between mean values. § Response was transformed using a logarithm of the response +1 to fit model assumptions. ǂ Response was transformed using a square root to fit model assumptions. Developmental Stage Key: (0 = cotyledon and true leaf formation, 1 = rosette, 2 = bolting, 3 = bud production, 4 = female floret production, 5 = anthesis, 6 = loss of male and female florets, 7 = seed development, 8 = seed maturity)
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Year and Population
Figure 2: Effect of growing degree days on silflower biomass yields when fall and spring planting over 2015-16 and 2016-17 at St. Paul, MN over two different groups of populations.
59
Year and Population
Figure 3: Effect of growing degree days on silflower developmental stage when fall and spring planting over 2015-16 and 2016-17 at St. Paul, MN over two different groups of populations.
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