Effect of plant density on oil yield of safflower

1Universidade Estadual do Oeste do Paraná, UNIOESTE, Pós-graduação em Energia na Agricultura. Rua Universitária, 2069 – CEP:85.819-130, Bairro Faculdade, Cascavel, (PR), Brazil. 2 Universidade Estadual Paulista “Júlio de Mesquita Filho” Departamento de Produção e Melhoramento Vegetal – Botucatu (SP), Brazil. 3Universidade Estadual do Oeste do Paraná, UNIOESTE, Campus de Marechal Cândido Rondon Centro de Ciências Agrárias. Rua Pernambuco, 1777 Caixa Postal: 91. CEP: 85960-000 Marechal Cândido Rondon (PR), Brazil.


INTRODUCTION
Due to the growing concern of power generation without damaging the environment, bio-energy species that have favorable characteristics in this regard are under study; thus, highlighting the safflower crop (Carthamus tinctorius L.), though little is still known in Brazil (Santos and Silva, 2015).The culture has productive potential, easy adaptability and good resourcefulness in clayey and sandy soils (Santos et al., 2015).
Strategies and cultural managements should be studied in order to determine and increase the productive potential of this new culture so that the safflower can become a culture for production systems in Brazil.According to Mertz et al. (2009), numerous factors determine the development and productivity of cultivation; *Corresponding author.E-mail: mari_marinez@hotmail.com Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License however, the ideal population of plants or the stand is important in achieving sustainability.
Due to the plant characteristics, safflower can compensate for the spatial variation by producing secondary and tertiary heads by plants with more branches formation in the plant (Elfadl et al., 2009), since the plant morphology depends on the degree of intraspecific competition (Gimplinger et al., 2008).Studies indicate the desired density of 40-50 plants per m 2 and up to 70 plants per m 2 in light soils (Espig and Rehm, 1991).However, increased oil content (Emami et al., 2011), grain yield (Ozel et al., 2004) and oil yield (Alessi et al., 1981) were found with increase in the plant density.
Important factors of production should be taken into consideration, in order to achieve greater productivity, highlighting the spatial arrangement of plants.In search of the optimum population for production, given the scarcity of information and with the hypothesis that the population density affects safflower production, the study aimed to evaluate the growth, yield components and grain production of safflower oil with regards to population densities in two growing seasons.

Location and climatic conditions
Two experiments were conducted in 2014 in Cascavel-PR, Brazil, with geographic coordinates of 24°56'40 "S and 53°30'31" W and an average altitude of 715 m.The behavior of the meteorological variables of the experiment is shown in Figure 1.
The soil of the experimental area was classified as Rhodic Acrudox (Soil Survey Staff, 2010).The experimental area was under no-tillage system for over 20 years, with crops such as corn or soybeans in the summer crops and oats or wheat in the fall/winter seasons.The chemical characteristics are presented in Table 1.

Experimental set-up
The first growing season was characterized by sowing on April 30, 2014 (autumn), and the second growing season on July 30, 2014 (winter).Sowing IAPAR genotype was performed manually.There was no need to apply pesticides and cultivation was carried out manually.

Treatments and experimental design
A randomized-blocks design with three replications was used.Four seed densities (5, 10, 15 and 20 seeds m -1 ) were sown.Each plot consisted of four rows measuring 4 m long.

Traits evaluated
When the plants showed 50% of flowering in 80 and 60 days after emergence during the autumn and winter seasons respectively, the plant height and the distance between the soil level and the plant apex, six plants at random within each plot, was determined, by measuring with graduated tape.The number of branches per plant and capitula was determined by counting.When the crop had 50% of flowering was also determined, by collecting six plants at random in each plot, measuring the stem diameter with the aid of a digital caliper and the basal region of the stem.
At harvest, 160 and 140 days after emergence during autumn and winter seasons, respectively, the grain yield was determined, after manual threshing and cleaning of the grains, each portion was harvested from plants collected from a linear meter, and the values expressed in kg ha -¹, making the moisture content to be 12%.The 1000-seed weight was performed by counting sub-samples of 100 grain per plot.The samples were weighed on a precision scale to two decimal places, making the moisture content to be 12%.The 1000-seed weight was determined in accordance with the Rules for Seed Analysis (Brasil, 2009).
Oil content was determined from a TD-NMR in a SLK-SG-200 spectrometer (Spin Lock Magnetic Resonance Solutions, Malagueño, Córdoba, ARG) at 25°C, equipped with a permanent magnet of 0.23 T (9 MHz for 1H) and a probe with 13 × 30 mm of useful area.The Condor IDE software with CPMG pulse sequence and Qdamper (Colnago et al., 2011), expressed on a dry basis (% DB) was used.Oil yield (kg ha -1 ) was calculated as the product of oil content and seed yield.

Statistical analysis
Satisfactory adjustment that provided higher coefficient of determination higher than 70% and present minimal significance level of 5% of probability in the coefficients was considered.To perform regression analysis, the program Sigma Plot 11.0 (Jandel Scientific, Sausalito, CA, USA) we used.

RESULTS AND DISCUSSION
The height of safflower plants (Figure 2A) was affected by plant densities, with densities of 14 and 16 plants per m (311 and 355 thousand plants per ha, accordingly) resulting in maximum heights for fall and winter, accordingly.In early sowing of autumn, the plants received more solar interception which favored growth, requiring fewer plants per meter for maximum growth, since the plant morphology is reflected by the degree of intraspecific competition (Gimplinger et al., 2008).In winter, due to the lower growth, the density of plants is necessary, but the plant height observed in this study is substantially lower (67%) in the late seeding (0.74 m) in relation to the early one (1.24m).These results are aligned to those observed by Omidi and Sharifmogadas (2010) in Iran, since both the delayed sowing as well as the lowest density negatively affected the safflower plant growth, although the maximum height has been achieved with a greater population than the present study.Tarighi et al. (2012) also in Iran found that the lower density of plants per hectare resulted in lower plant height.Bellé et al. (2012) in Brazil did not observe greater growth of plants when the density increased from 48 to 128 plants per m 2 in sowing autumn/winter and spring/summer.There are also reports that indicate that the increased density has limited the height of the plant (Gonzalez et al., 1994;Elfadl et al., 2009).Plant densities effect of safflower growth is likely to occur, since the greater or lesser light interception by plants reflect the plasticity of   (Zarei et al., 2011;Necdet et al., 2007;Omidi and Sharifmogadas, 2010;Amoughin et al., 2012).The decrease in stem diameter (Figure 2B) with the increase in the population during fall can be related to the bigger internode lengthening due to competition for solar radiation, as suggested by Bellé et al. (2012).Nevertheless, the greatest increase in autumn contributed to the greater diameter, because the plant has a longer cycle.In winter cultivation, the lowest growth of the plants in relation to fall may not affect internode lengthening, making the stem diameter to have 8.3 mm on average.Nevertheless, Bellé et al. (2012) reported reduction in stem diameter during autumn/winter and spring/summer with increased densities for 128 plants per m 2 .The reduction of the number of branches per plant (Figure 2C) and the consequent decrease in the number of chapters per plant (Figure 2D) in autumn cultivation, clearly demonstrates that increasing the competitiveness among plants affect these variables, as reported by other authors and common in the literature (Azari and Khajehpour, 2003;Elfadl et al., 2009;Bellé et al., 2012;Emami et al., 2011;Amoughin et al., 2012;Santos et al., 2016).In the second crop, in winter season, the lowest growth of the plant was also reflected in the average values of 6.4 and 9.3, branches and chapters per plant, accordingly.The plant growth components are most affected by densities in early cultivation, since high temperatures and increased water availability result in a greater cycle and the effect is more noticeable, since growth is also the result of interactive phenomena between genetic characteristics, physiological, ecological and morphological of the plant (Farooq et al., 2009).
In the present study, the plant densities did not affect the weight of 1000 grains in both seasons (Figure 3A), which is in line with the results of experiments with population densities of Malvi et al. (1988) with winter safflower India in (Azari and Khajehpour, 2005) with  2009) with safflower in Germany summer.It is noted that despite reducing the number of chapters per plant and the possibility of having reduced number of seeds per plant, population densities do not compromise the grain weight, showing safflower capacity to react to the plant density, which is due to an undetermined cycle of culture according to Elfadl et al. (2009).
The grain yield (Figure 3B) benefited by the maximum density of plants in winter (20 plants per m) and up to 16 plants per meter (355,000 plants per ha) in fall.This result can be attributed to an increased number of chapters per area as the number of chapters per plant was reduced.The increase in the number of plants has led to increased productivity, according to the results found by Alessi et al. (1981), Ozel et al. (2004) and Kakhaki et al. (2007), in a study of the same nature with safflower plants.These results are also similar to the findings of Mane and Jadhav (1994), where seed production increased as plant density increased from 7.5 to 22.5 m 2 plants.Nevertheless, different results were observed by Elfadl et al. (2009), who found no significant impact on the production of seeds, which according to the authors is due to safflower capacity to compensate for the variation in plant density.The greatest need of plants per meter in cultivation in winter season (444,000 plants per hectare) to approach the early crop yield of autumn, is due to the slower growth of plants in winter, causing a reduction of the cycle, which afforded lower compensation rate.
The oil content (Figure 3C) averaged 23.3% in autumn, below the ideal range of 35 to 45% (Kaya et al., 2003;Mahasi et al., 2009), although similar values to that of Elfadl et al. (2009)  and Norman (1966) reported a slight effect.In winter, low density damaged plants safflower oil content, whereas 16.7 plants per meter resulted in 26% oil.A likely explanation for the increased oil content with increasing planting density, can be correlated to a substantial grain yield increase (583 to 3335 kg ha -1 ) in winter cultivation with the increase of plants per meter, that is, the oil content was more sensitive in winter due to contrasting grain yield situation.Sounda et al. (1983) also reported that the low plant density (5 plants m 2 ) significantly reduced the oil content in safflower sown in winter.According to Rathke et al. (2006), optimizing the content of oil involves balancing the protein synthesis and crude oil in the grains as well as energy and carbon dioxide (CO 2 ), so, the winter crops afforded conditions for this variable.
The oil yield (Figure 3D) is a combination of grain yield and grain oil content, thus follows a grain yield similar results, since the effects on oil content is limited to compensation.Despite this, the oil yield in fall (992 kg ha -1 ) is only 15% higher than in winter (858 kg ha -1 ), a difference that was 27% for grain yield between seasons.In this regard, it was observed that increasing densities favored the winter safflower.In summer, 15 plants per meter were sufficient for maximum productivity of oil.

Conclusion
The oil content improved with increase in plant densities

Figure 1 .
Figure 1.Behavior of meteorological variables of precipitation, mean temperature, wind and solar radiation in safflower cultivation during autumn and winter seasons in Cascavel, PR, Brazil, in 2014.

Figure 2 .
Figure 2. Plant height (A), diameter of stem (B), number of branches per plant (C) and number of chapter per plant (D) in autumn and winter seasons according to plant dens

Figure 3 .
Figure 3. 1000-seed weight (A), yield (B), oil content (C) oil yield (D) in autumn and winter seasons according to plant density.

Figure 3 .
Figure 3. 1000-seed weight (A), yield (B), oil content (C) oil yield (D) in autumn and winter seasons according to plant density.

Table 1 .
Soil chemical attributes in the depth of 0 to 0.20 m in the experimental areas.