Characterization of Northern Spring Flax as a Winter Crop for Southeast Texas

Increasing interest in biodiesel production led to flax being evaluated as a potential biodiesel crop throughout the USA. The objectives of this study were 1) to determine if northern spring flax varieties can be grown as a winter crop in the southeast Texas environment, 2) characterize the varieties under the southeast Texas environment and 3) to determine if northern spring flax varieties can be grown on a laser-leveled field with 17.8 cm row spacing rather than raised beds. In this study, five northern spring flax varieties, Nekoma, Omega, Pembina, Prairie Thunder and York were grown as a winter crop in Beaumont, Texas on a laser-leveled field. The flax varieties were characterized with respect to morphology, phenology and physiology. In the present study, Omega and Pembina were taller compared to the other varieties. Nekoma had more branches, whereas Omega had more immature capsules per plant, compared to other varieties. Leaf photosynthetic rate was higher in Omega and Prairie Thunder, compared to other varieties. At harvest, Omega and York had more mature capsules, and greater capsule weight and shoot weight per plant, compared to other varieties. Due to delayed machine harvest, there was decrease in flax seed yield due to capsule dehiscence and shattering. Omega had more capsule dehiscence and shattering, compared to other varieties. Seeds of Nekoma and Pembina had more oil content and Omega and Pembina had more protein content. All the above flax varieties have potential to be used as an oilseed crop for biodiesel production in southeast Texas.


Introduction
Flax (Linum usitatissimum L.) is an oilseed and fiber crop (Jhala & Hall, 2010) that belongs to the family Linaceae and has its origin in Europe and Asia (Berglund & Zollinger, 2002).It is the third largest natural fiber crop and one of the five major oil crops in the world (Pali & Mehta, 2014).Flax is a well established crop in many countries due to its positive health effects and numerous industrial uses.According to the Food and Agricultural Organization (FAO, 2010), the six major countries that produce flax are Canada, China, India, Russia, Kazakhstan and Ethiopia.In the USA, North Dakota, South Dakota, and Minnesota produce the majority of the flax seed and North Dakota is the leading state for flax production (Berglund & Zollinger, 2002).In Texas, flax was grown in the coastal area in the 1950's, but due to severe drought over years, Texas flax acreage declined and has remained negligible since the 1980's (National Agricultural Statistics Service-United States potentially affect plant stand (Darapuneni et al., 2014a).Cooler temperature (< 16 o C) can delay capsule maturity and reduce the number of seeds per capsule and total seed yield.High temperatures (> 20 o C) during reproductive phase reduce seed number per capsule, seed weight, oil yield and quality (Dybing & Zimmermen, 1965).Under hot and dry conditions, irrigation at flowering and grain filling considerably increases oil yield and quality (Tiwari, Dixit, & Saran 1988;Dutta, Ram Mohan Rao, & Singh, 1995).However, irrigation or rainfall during the latter part of the cropping season can also result in a flush of new tillers causing uneven ripening (Diepenbrock & Iwersen, 1989).
Flax can be been grown under a wide range of soils (medium to heavy textured soils with pH 6; Hocking, Randall, & Pinkerton, 1987).Flax grows best on well-drained conditions, hence, it is typically grown on raised beds.Increasing interest in biodiesel led to flax being evaluated as a potential biodiesel crop throughout the U.S. Identifying appropriate varieties for a particular climatic region is essential for crop development and improvement.The objectives of this study were 1) to determine if northern spring flax varieties can be grown as winter crop in the southeast Texas environment, 2) to characterize the varieties under the southeast Texas environment and 3) to determine if northern spring flax varieties can be grown on a laser-leveled field with 17.8 cm row spacing (similar to that of rice) rather than raised beds.

Plant Culture and Climatic Conditions
The field experiments were conducted at the Texas A&M AgriLife Research Center at Beaumont, Texas, USA (29 o 57′N lat; 94 o 30′W long) during 2010 and 2011.The soil at this site is an Entic Pelludert (fine, montmorillonitic, and thermic), with a sand, silt, and clay composition of 3.2, 32.4, and 64.4%, respectively (Samonte et al., 2006).The soil at this site has poor drainage (Natural Resources Conservation Services-United States Department of Agriculture [NRCS-USDA], 2006).Each plot was 10.4 m 2 and consisted of 8 rows.In this study, flax spring varieties from Canada and the Northern US were planted as winter crop in Southeast Texas.The five flax varieties: Nekoma, Omega, Pembina, Prairie Thunder and York (Table 1) were grown on a laser-leveled field (0.2% slope gradient).Planting was done on October 20, 2010.A drill (John Deere, Illinois, USA) was used to plant the seed at a depth of 2.5 cm.The seeding rate was 45 kg/ha.On October 27, 2010, 75% emergence was seen.Nitrogen, phosphorus and potassium were applied at the rate 163 kg/ha, 49 kg/ha and 49 kg/ha, respectively, at 91 days after planting and 126 days after planting.Harvesting was done using an Almaco plot harvester (Almaco, Iowa, USA), 196 days after planting.2).The maximum and minimum relative humidity varied between 91% to 95% and 34% to 55% (Table 2).The monthly rain fall, wind speed and solar radiation varied between 1.2 mm to 129 mm, 135 km/day to 238 km/day and 10 MJ/m 2 /day to 23 MJ/m 2 /day, respectively (Table 2).

Morphology, Phenology and Dry Weights
At harvest, plant height was measured; numbers of branches per plant and mature capsules per plant were counted.Date of flowering was recorded, and immature capsules per plant were counted.Shoot and capsule dry weights per plant were determined at harvest.

Mechanical Harvest
Machine harvest was delayed due to poor weather conditions.Each plot was separately harvested using an Almaco plot harvester (Almaco, Iowa, USA).Harvest was conducted 189 days after emergence (DAE).The harvested seed was dried in a sack drier to a moisture level of 10% which is the recommended moisture level to safely store flax seed.

Leaf Photosynthesis, Seed Oil and Protein Content
The net photosynthetic rate (P N ) of the penultimate leaves was measured using a LI-6400 portable photosynthesis system (LI-COR Inc., Lincoln, Nebraska, USA), 148 DAE.The P N was measured between 1000 h and 1200 h.When measuring P N , the light intensity, temperature and CO 2 concentration in the leaf cuvette were set to 1500 µmol m -2 s -1 , 25 °C and 390 ppm, respectively.Seed oil content was measured using Nuclear Magnetic Resonance (NMR; Bruker Minispec MQOne Seed Analyzer, Bruker BioSpin Corporation, Billerica, Massachusetts, USA) and seed nitrogen using FP-528 Nitrogen/Protein analyzer (LECO Corporation, St. Joseph, Michigan, USA).

Experimental Design and Data Analysis
The experiment was setup as randomized complete block design (RCBD).There were two blocks (two locations) and five treatments (varieties), with eight replications in each block.The data were analyzed using the PROC GLM procedures in SAS software (SAS statistical analysis package version 9.2, SAS Institute, Inc., Cary, NC) to test the significance difference between blocks and among the varieties for different parameters measured.The means were separated using Tukey's least significant difference (LSD) at an alpha level of 0.05.If there was no significant difference among the blocks for a parameter, then the values from both the blocks for that parameter were used to obtain the mean and error.The standard errors of the mean were also calculated and presented in the graphs as error bars.

Morphology, Phenology, and Dry Weights
There was no difference between the blocks for plant height, numbers of branches, immature and mature capsules, capsule weight and shoot dry weight per plant.However, Omega (56.4 cm) and Pembina (56.5 cm) were taller compared to the other varieties at harvest.Nekoma, Prairie Thunder and York were 7%, 9% and 12% shorter compared to Omega (Figure 1A).In this study, Nekoma (2.4 branches plant -1 ) had more branches per plant than other varieties at harvest.Nekoma had 43% more branches per plant compared to Omega, whereas Pembina, Prairie Thunder and York had 67%, 77% and 57% less branches compared to Omega (Figure 1B).(Dixit et al., 2012).Flax seed oil has potential to be used for biodiesel (Dixit, Kanakraj, & Rehman 2012).Three main factors which can affect flax seed production are genetic makeup or the varieties, and environmental and agronomic factors (Anastasiu et al., 2016).In the present study, we evaluated the varieties, environmental and agronomic factors affecting flax seed production.Canadian and Northern U.S. flax varieties were grown as a winter crop in the southeast Texas environment on a laser leveled field.In the present study, flax spring varieties from Canada and the Northern U.S. performed well under southeast Texas conditions on a laser-leveled field.Similar results were reported by Darapuneni, Morgan, Ibrahim, and Duncan (2015), where flax varieties performed under south Texas conditions.However, the average flax seed yield in the present study was 700 kg ha -1 , which was much below the average World flax seed yield (943 kg ha -1 ; Berti et al., 2010) and recent south Texas (College Station, Texas) average flax yield (1350 kg ha -1 ; Darapuneni et al., 2015).However, the flax yield in the present study (Beaumont, Texas) was similar to that of yield at McGregor, Texas (Darapuneni et al., 2015).In the present study, the decrease in the seed yield was due to high rainfall (capsule dehiscence and shattering) and high temperatures during seed development, whereas, the decrease in yield at McGregor Texas was due to cold injury (Darapuneni et al., 2015).
Flax is mainly adapted to temperate climates (Adugna & Labuschagne, 2003).Temperature plays an important role in determining flax plant stand, plant height, time to reach maturity, seed yield, oil content, and oil composition (Cross et al., 2003;Darapuneni et al., 2015).In the present study, the temperature during the cropping season was between 4 o C and 30 o C. Hence, no cold injury was noticed in this study.Temperatures below -2 o C can cause severe cold injury and can potentially affect plant stand (Darapuneni et al., 2014a).In this study, during the vegetative growth the temperatures were below 20 o C, which is favorable for flax vegetative growth.Temperatures above 20 o C can hasten senescence of the stem and leaves (Dybing & Zimmerman, 1965).In the present study, temperatures were higher than 20 o C (24-30 o C), during seed development.It has been reported that high temperatures during reproductive growth decreases number of mature seed produced per capsule, seed weight and oil content (Dybing & Zimmerman, 1965).In addition, during the seed development there was high rainfall (165 mm) causing capsule shattering.
In the present study, flax varieties differed with respect to plant height, number of capsules per plant, photosynthetic rate, yield and oil content.Similar differences among flax varieties were seen with respect to morphological parameters and yield (Berti et al., 2010;Darapuneni et al., 2015).Under optimum conditions flax seeds can yield up from 33-47% oil content (Dixit et al., 2016).Similar results with respect to flax oil content were reported by Darapuneni et al. (2015).In the present study, the oil content in the varieties varied from 40.7% to 42.8%.Differences in oil content among flax varieties were reported by Pali and Mehta (2014).There was no correlation observed between the seed yield potential and seed oil content and/or seed protein content.Darapuneni et al. (2015) also showed there was no correlation between seed yield and seed oil content.

Conclusion
In conclusion, this study indicates that northern spring flax varieties grown as a winter crop in southeast Texas (Beaumont, Texas) environment on a laser-leveled field with 17.8 cm row spacing performed well with respect to morphology, phenology, physiology, yield and oil content.Due to delayed machine harvest (bad weather-heavy rainfall), there was a decrease in crop yield due to capsule dehiscence and capsule shattering.Genotype Omega had more capsule dehiscence and shattering, compare to other varieties.All the above flax varieties have potential to be used as oilseed crop for biodiesel production in southeast Texas (Beaumont, Texas).

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Table 1 .
Flax varieties characterized for Southeast Texas region during 2010-2011 During the cropping season, the monthly maximum and minimum air temperatures varied between 15 o C to 30 o C and 6 o C to 19 o C (Table2).The maximum and minimum soil temperatures varied between 14 o C to 30 o C and 9 o C to 23 o C (Table

Table 2 .
Average monthly minimum and maximum air and soil temperature, relative humidity, rainfall, wind speed and solar radiation during the cropping season(2010)(2011)in southeast Texas (Beaumont, TX) Note.† T max , mean monthly maximum temperature in o C; ‡ T min , mean monthly minimum temperature in o C; § RH max , mean monthly maximum relative humidity in %; ¶ RH min , mean monthly minimum relative humidity in %; # RF, rainfall in millimeter (mm); * WS, mean monthly wind speed in kilometers per day (km/day); • SR, mean monthly solar radiation in mega joules per square meter per day (MJ/m 2 /day).