The impact of planting dates and hybrid selection on sunflower seed yield and oil content

Abstract

Suitable planting dates and hybrid selection are crucial in optimising yield, component traits and oil production in sunflower (Helianthus annuus L.). In South Africa, there is limited information on the effects of planting dates on currently available sunflower hybrids in the marketplace. This study aimed to investigate the impact of planting dates on sunflower seed yield, oil content and oil yield, and to discern optimal planting dates for selected sunflower hybrids. Nineteen commercial sunflower hybrids were evaluated at three planting dates and three consecutive seasons in Potchefstroom, South Africa. The study used a complete block design with three replicates, and the standard analysis of variance was conducted. Significant differences were detected among seasons, planting dates, hybrids, and their interactions. The mean seed yield varied from 1.86 (LG 5678 CLP) to 2.50 tonnes ha⁻¹ (PAN 7160 CLP). The oil content varied from 37.23 (P 65LP 54) to 53.16% (SY 3970 CLP), and the oil yield ranged from 0.74 (AGSUN 5101 CLP) to 1.25 tonnes ha⁻¹ (LG 5710). Planting sunflowers in November and December resulted in the highest seed yield, oil content and oil yield, while planting in January and early February showed linear declines. January planting reduced 1 to 20%, 2 to 10%, and 3 to 26% in seed yield, oil content and oil yield, respectively. February planting significantly reduced seed yield by 72%, oil content by 20% and oil yield by 77%. The study recommended November and December as optimal sunflower planting dates in South Africa.

Keywords:

• crop performance
• Helianthus annuus L
• oil yield
• optimal planting

Introduction

Sunflower is an annual oilseed crop globally cultivated across 27 million hectares, providing 51 million metric tonnes during the 2022/23 growing season. This accounted for 8% of the world oilseed market (USDA 2023). Sunflower oil is one of the major vegetable oils used in the food industry. The high quality, edibility and high protein content of the oil is valuable to produce various commercial products for food, feed, cosmetics and biofuels (Ahmad et al. 2014; Papatheohari et al. 2016). Most livestock feed rations rely on sunflowers as the primary energy source. Soybean yields more protein meals and is widely used in the animal feed market, while sunflower seed has higher oil yields and is valuable for human consumption. Hussain et al. (2018) reported that sunflower seeds contain approximately 40–50% oil and 17–20% protein.

The major global sunflower producers include Russia, Ukraine, the European Union and Argentina (USDA 2023). These countries contribute significantly to the global sunflower oil markets (78% of global outputs). South Africa contributes 1% of the world’s sunflower production and is among the leading producers of sunflower seeds in the southern African region (USDA 2023).

Sunflower is the fourth largest grain crop produced in South Africa after maize, wheat and soybean. Between 2012 and 2022, an estimated 753 000 tonnes of sunflower seed were produced per annum (Meyer 2023). In 2022, 670 700 hectares of sunflower were cultivated in South Africa due to strong market prices owing to global market dynamics and late rains that delayed summer plantings. There was a 40% increase in the area planted to sunflower in 2022 (BFAP 2022). The Bureau for Food and Agricultural Policy (BFAP) Baseline, Agricultural Outlook 2022–2031, predicts that the area under sunflowers will stabilise at around 500 000 hectares in the medium term. Despite stabilisation of cultivation, production is projected to increase by 23% over the next decade, reflecting technological advancements and continuous improvement in production practices. The area of production is sufficient to meet the domestic demand. Furthermore, the latest sunflower breeds and seed technologies provide promising results in high-oil-content production (BFAP 2022). High-oil-content cultivars will support the relative competitiveness of the local sunflower industry.

Sunflower is a temperate zone crop that performs well under various climatic and soil conditions (Canavar et al. 2010). It combines high yield with an excellent adaptation capacity (Agele 2003). It is grown under rain-fed systems due to its moderate drought tolerance, attributed to its well-developed and profoundly deep root system that efficiently utilises soil nutrients and moisture (Jaafar et al. 1993; Stone et al. 2002). However, from early flowering to the grain-filling stages, sunflower is particularly sensitive to drought (Unger 1983; Göksoy et al. 2004) and heat stress (García López et al. 2014).

Environmental factors, including air temperature, day length, intercepted solar radiation and rainfall, affect sunflower growth and development (Van der Merwe et al. 2013; Pekcan et al. 2015; Robert et al. 2016). Fluctuations in air temperature and moisture availability impact the quantity (grain weight) and quality of oil accumulation in sunflower (Aguirrezábal et al. 2003; Hassan et al. 2011). Air temperature is the most crucial parameter affecting the plant’s development and fatty acid accumulation (Ritchie and NeSmith 1991). The optimal air temperature for average stress factor growth and development is around 28 °C (Villalobos et al. 1996). Chimenti and Hall (2001) demonstrated that a 1 °C increase above 25 °C during the grain-filling stages could lead to a reduction of approximately 1.2% in final grain weight. Van der Merwe et al. (2015) reported that sunflower seed yield and oil quality were significantly affected by high air temperatures experienced around 24 °C/36 °C night/day during the grain-filling stage in South Africa. High oleic acid genotypes showed an increase in grain yield under these air temperatures but a significant decrease of up to 6% in oil content.

Sunflower is most sensitive to yield loss with heat stress 12–19 days after anthesis (DAA), while oil quality components were most sensitive during 19–26 DAA (Rondanini et al. 2003). Seed oil concentration is typically reduced when air temperatures remain above 25 °C during grain filling (Weiss 2000). Rondanini et al. (2003) observed that seeds produced after a short-term heat stress period of 37 to 40 °C during grain filling (12–26 DAA) had significantly lower oil concentrations. Delayed grain filling due to later planting dates, which experience lower air temperatures or reduced solar radiation, has been linked to lower oil concentrations (Leon et al. 2003; Echarte et al. 2010). Although sunflower is considered moderately tolerant of drought, several studies have demonstrated that drought stress significantly reduces seed and oil yield, oil content and other essential yield traits in sunflower (Babaeian et al. 2011; Oraki and Aghaalikhana 2012; Ibrahim et al. 2016).

The impact of drought stress on sunflower productivity varies across different growth stages. For instance, early-season drought stress suppresses seed germination, stem elongation and leaf area. Drought stress at anthesis forms empty achenes due to pollen infertility (Fatemi 2014; Totsky and Lyakh 2015). Drought stress, whether during the vegetative or reproductive stages, can cause significant reductions in oil yield and quality (Hussain et al. 2008). Implementing drought-escape strategies, such as developing early maturation hybrids and adjusting planting dates based on the onset of dry periods in the summer season, have been suggested to increase sunflower yield (Kaya 2016).

The productivity of the sunflower is greatly influenced by prevailing weather conditions throughout its life cycle and implemented cultural practices (Oshundiya et al. 2014).

Among these practices, planting date is considered one of the most relevant management decisions in crop production systems (Popa et al. 2017). This practice establishes the environmental conditions experienced by plants during their life cycle, provoking significant variations in phenology, biomass accumulation, grain yield and seed quality (Andrade 1995). By anticipating the timing of critical crop growth stages, the exposure of sunflowers to the most stressful factors can be reduced. The optimal planting date depends on the latitude where the crop is planted. Soriano et al. (2004) suggest early planting in northern Argentina to avoid heat and water stress during flowering. On the other hand, in the south, planting is delayed, taking advantage of cooler air temperatures during grain filling. In the Mediterranean regions that have mild winters sunflowers can be planted even in late autumn or winter, resulting in improved water-use efficiency (WUE) and yield (Gimeno et al. 1989). With early plantings, more of the growing cycle occurs under low evaporative demand, so water productivity is higher, and high summer air temperatures during grain filling are avoided. The observed lower yields associated with late plantings have been variously hypothesised as being due to warmer air temperatures during the early growth period, which promotes excessive early stem growth (Beard and Geng 1982) and reduces time to flowering (Andrade 1995), followed by cooler air temperatures and reduced incident solar radiation post antheses, which affects the dynamics of grain filling. De la Vega and Hall (2002) found that delaying planting dates reduces sunflower grain and oil yields. Popa et al. (2017) reported that the early planting date increased grain oil content in all studied Romanian sunflower hybrids.

In South Africa, sunflowers are typically planted from November to mid-January, with the semi-arid Free State and North West provinces accounting for approximately 80% of the total sunflower cultivation area. Consequently, unpredictable adverse weather conditions often occur during the production season, significantly influencing seed yield and oil content. The effects of planting date on seed yield and oil content of sunflower hybrids currently available in the South African market remain largely unknown. Thus, the main objectives of this study were to investigate the impact of planting dates on sunflower seed yield, oil content and oil yield, and to determine the optimal planting dates for different sunflower hybrids to recommend desirable planning dates and hybrids.

Material and methods

Description of the study site

Nine trials were planted from October to early February during the 2018/2019, 2019/2020 and 2020/2021 growing seasons at Agriculture Research Council – Grain Crops in Potchefstroom, North West province, South Africa. Total rainfall and the mean minimum and maximum air temperature were recorded on site and are presented in Figure 1. Before planting, composite soil samples were collected randomly from different soil depths (0–150 mm, 150–300 mm and 300–600 mm). The soil samples were then sent to the ARC soil laboratory for soil analysis. The following soil fertility analyses were determined: soil pH (KCL), inorganic nitrogen (N-NO₃+ NH₄ extracted with 1:5 Ext – 0.1N K₂SO₄), phosphorus (P extracted using a 1:7.5 Ext. Bray 1 method), and (extracted with 1:10 Ext Amm. Acetate −1N, pH7) calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na); and organic carbon (C) (Table 1).

Figure 1: Monthly rainfall (mm), maximum air temperature (T_max), and minimum air temperature (T_min) (°C) recorded during the three growing seasons: (a) 2018/2019, (b) 2019/2020, and (c) 2020/2021 with three planting dates (D1) October and November planting, (D2) December planting, and (D3) January and February planting at Potchefstroom Research Farm, South Africa

Table 1: Physical and chemical properties of the soil of the study site during the three cropping seasons

Plant materials

Sixteen commercially available sunflower hybrids were selected from various local seed companies: six hybrids from Agricol, two from Lima Grain Zaad SA, three from Pioneer Seed, three from Pannar Seed and one from Syngenta. The test hybrids were planted in each trial during three consecutive growing seasons (2018/2019, 2019/2020 and 2020/2021) (Table 2).

Table 2: Characteristics of the commercial sunflower hybrids used in this study

Experimental design and treatments

Trials were laid out in a randomised complete block design with three replicates per season. Each plot consisted of four rows 10 m long with 0.90 m inter-row spacing, with a total plot size of 4 × 10 m × 0.90 m for each experimental unit. The middle 8 m in length of the two middle rows were harvested for yield and oil analysis. Planting dates under rain-fed conditions had to be based on yearly rainfall and soil moisture for that growing season. They could be on different calendar days every year. The following planting dates were compared: 18 October 2018, 9 November 2018 and 10 January 2019 (first growing season); 4 November 2019, 18 December 2019 and 5 February 2020 (second growing season); and 30 November 2020, 10 December 2020 and 21 January 2021 (third growing season). Trials have consisted of three factors: sixteen sunflower hybrids, three planting dates and three growing seasons.

Trial management

The recommended cultural practices were followed regarding field preparation, weed control and application of fertilisers. High plant populations were used at planting, and three weeks after emergence the plants were thinned to 38 000 plants per hectare to ensure good plant establishments. Based on the soil analysis, a basal application of 100 kg ha^–1 of N:P:K (3:2:1) (25%) + 5% Zn at planting was followed by a top dressing of 60 kg N ha^–1 applied four weeks after emergence. Fields were kept weed free by applying a pre-emergent selective herbicide (Metagan Gold-Syngenta, South Africa) just after planting and mechanical weeding throughout the season as required.

Data collection

Seed yield

Heads formed in the middle two rows were bagged with monofilament bags to prevent damage caused by feeding birds and harvested by hand at physiological maturity. After the heads were threshed and the seeds were cleaned, the seed moisture content was measured using a moisture meter. The seed yield for each hybrid was calculated based on the fresh weight data per plot, adjusted to 9% moisture. The resulting seed yield for each plot was expressed in kilogrammes per plot (kg plot^–1) and then converted to tonnes per hectare (t ha^–1).

Seed samples (500 g) from each harvested plot were sent to the Southern African Grain Laboratory for oil content analysis. Oil yield (t ha^–1) was calculated using the formula: seed yield (t ha⁻¹) × oil content (%).

Determination of oil content

The moisture content of the seed samples was determined; the seeds were weighed, dried in an oven at 105 °C for 5 h according to Agri-Laboratory Association of Southern Africa (Agri LASA methods version 2.1), and then weighed again. Moisture content was then determined using the following formula: seed weight before and after oven drying. Before chemical analyses, samples were milled using a Retch ZM 200 mill with a 1.0 mm screen. In-house method 024, Southern African Grain Laboratories (SAGL), North Carolina, USA, was used to determine the crude fat percentage in each sample. Fat was extracted using petroleum ether and the Soxhlet extraction apparatus. The solvent was removed through evaporation as the residue was dried at ∼100 °C. The dried residue (fat) obtained was weighed and expressed as a percentage of crude fat (or ether extract). The following formula was used for the calculation of fat percentage (%) on an ‘as is’ basis: (1) $\text{\%}\mathrm{Fat}\left(\mathrm{as}\mathrm{is}\right)=\left[\left(\mathrm{B}-\mathrm{A}\right)-\left(\mathrm{BB}-\mathrm{AB}\right)\right]÷\mathrm{C}\times 100$(1) where: A = mass of clean flask before extraction (g); B = mass of flask with fat (after fat extraction) (g); AB = mass of clean blank flask before extraction (g); BB = mass of blank flask after fat extraction (g); and C = weighed sample mass (2 g)

To compensate for any amount of fat present in the petroleum solvent, ether was used as a blank with every sample set to determine the subtraction value.

Data analysis

Seed yield, oil content and oil yield data were subjected to analysis of variance (ANOVA) for each growing season and planting date, followed by a combined analysis of variance across planting dates per year (pooled). SAS software (Version 15.2, SAS 9.4 for Windows 5th edition, SAS Campus Drive, Cary, North Carolina, USA) was used to determine the effects of the year, hybrid, planting dates and interactions on studied parameters, Levene’s test (Levene 1960) was used to test for homogeneity of variances of planting dates across the seasons, and the Shapiro–Wilk test (Shapiro and Wilk 1965) was used to test the normality of the data before combining data from all trial sites across the three seasons. Means were separated by Fisher’s unprotected least significant difference (LSD), provided that the F probability from the ANOVA was significant at the 5% (p ≤ 0.05) level of significance.

Results and discussion

Weather conditions during the growth seasons

The rainfall and air temperatures experienced during the three growing seasons and at the three planting dates during each growing season varied. In the 2018/2019 growing period, the total rainfall was 360 mm, much lower than the long-term average of 658 mm. Approximately 20% of the rainfall was received in January and 40% in April. The mean maximum and minimum air temperatures were two degrees higher than the long-term average. For the 2019/2020 growing season, the rainfall was 829 mm, which exceeded the long-term average. More than half of this rain was received in December (33%) and January (29%). This season’s mean maximum air temperature was two degrees higher than the long-term average, while the mean minimum air temperature was one degree higher. In the 2020/2021 growing season, the rainfall (424 mm) was less than the long-term average, with the majority occurring in January (41%). The mean maximum air temperature was one degree higher, while the mean minimum air temperature was the same as the long-term average (Figure 1a, b, c). Rainfall received on the first, second and third planting dates, respectively, was 360 mm, 358 mm and 269 mm (first growing season), 829 mm, 612 mm and 286 mm (second growing season), and 424 mm, 421 mm and 237 mm (third growing season). Rainfall was significantly higher on the first and second planting dates compared to during the third planting date in all three growing seasons.

Seed germination is a complex process affected by various factors, with moisture availability being the most critical (Luan et al. 2014). During the first planting period starting on 18 October 2018 (in the first growing season), germination and leaf emergence coincided with a dry period when only 4% of the total rainfall occurred; 40% of the rainfall was received in April after grain filling (Figure 1a). These conditions may explain why sunflowers from the first planting date produced a lower seed and oil yield than those from the second and third planting dates. Additionally, the seed yield and oil yield reduction between November and January plantings was insignificant (Table 3). This result suggests that the timing of rainfall during the germination and grain-filling stages significantly influences sunflower productivity, with early-season drought stress having a negative impact on seed and oil yield. This finding agrees with Fulda et al. (2011) and Fatemi (2014), who reported that early-season drought stress suppresses germination, stem elongation and leaf area.

Table 3: Mean seed yield, oil content and oil yield of the tested sunflower hybrids at different planting dates over three growing seasons

In the second and third growing seasons, the February and January plantings coincided with a dry period from early flowering to the grain-filling stage. The total rainfall during February and January planting was only 286 mm and 237 mm, respectively (Figure 1b, c), coinciding with low air temperatures in February planting during the anthesis and grain filling. This climate scenario shortened the grain-filling period, resulting in lower seed yield, oil content and oil yield than for the November and December plantings. These results confirmed those of Totsky and Lyakh (2015), who concluded that drought stress experienced during anthesis results in the formation of empty achenes due to pollen infertility, resulting in lower yields.

The effects of year, planting date and hybrid on assessed traits

The combined ANOVA revealed a highly significant (p ≤ 0.001) effect of year, planting date, hybrids, and their interactions on seed yield, oil content and oil yield (Table 4). This implies the presence of variability between hybrids and the environments, which suggests that some of the hybrids were superior to others in terms of these traits. The highly significant interactions of year (Y) × planting date (D), planting date (D) × hybrid (H), and year (Y) × planting date (D) × hybrid (H) for these three traits showed that the performance of hybrids differed in different planting dates and growing seasons. The interactions between year and planting dates (Y × D) showed a substantial effect, accounting for 50% of the variation in seed yield and 43% in oil yield, followed by planting date contributing to 26% of the variation in seed yield and 29% in oil yield. Hybrids had less effect, accounting for 5% and 10% for seed and oil yield, respectively, followed by other interactions. In terms of oil content, the effects of the hybrids were the highest (49%), followed by planting date (18%), year (14%) and their interactions. These results concur with those obtained by Zheljazkova et al. (2011), which confirm that hybrid and planting dates significantly affect oil yield in sunflowers. Balalić et al. (2012) found that the hybrid predominantly influenced oil content, followed by the year and planting date.

Table 4: Combined analysis of variance and mean square values for seed yield, oil content and oil yield of 16 sunflower hybrids planted on three different planting dates over three growing seasons

Furthermore, according to Balalić et al., oil yield was most influenced by the year, then by the planting date and hybrid. Popa et al. (2017) reported that the oil content in sunflower seeds was highly significantly affected by year, planting date, hybrids, and most interactions between these factors. Therefore, based on these results, selecting the most suitable sunflower hybrid for optimising oil yield in sunflower cultivation should be a primary consideration for farmers. However, it is essential to acknowledge that the choice of planting date remains a crucial management factor, and it should be carefully coordinated with the selected hybrid to maximise yield potential.

The effect of year and planting date on seed yield, oil content and oil yield during the study is presented in Table 3. Seed yield, oil content and oil yield showed significant differences among the three years. The highest mean seed yield (2.26 t ha^–1) was recorded during the 2020/2021 growing season, while the highest mean oil content (46.02%) and oil yield (1.01 t ha^–1) were recorded during the 2018/2019 growing season. The lowest mean seed yield, oil content and oil yield (2.08 t ha⁻¹, 41.88% and 0.91 t ha^–1) were recorded during the 2019/2020 growing season, respectively, which could be attributed to late planting in February. The plants from this planting date showed good vegetative growth initially. However, drought stress and extremely low air temperatures during anthesis and grain filling produced empty achenes. These findings confirm those of Lawal et al. (2011), who reported that decreased rainfall at the end of the growing season leads to inadequate moisture availability during the reproductive stages, negatively affecting seed production. The authors also indicated that sunflowers planted late in the season produce smaller heads with tiny hollow seeds in the centre.

Significant variations among the tested years for seed and oil yields indicated that crop yield is a complex trait that can be influenced by genotype, environmental factors and management practices. This was supported by studies conducted by De la Vega and Hall (2002) and Izquierdo et al. (2006), who argued that sunflower seed and oil yields depend mainly on the environment, which varies over years, locations and planting dates.

During our study, the seed yield at the different planting dates varied between 3.02 t ha⁻¹ (18 December 2019) and 0.84 t ha^–1 (5 February 2020). Delaying the planting date until January reduced seed yield by 1% (10 January 2019) to 20% (21 January 2021), while planting delayed until February reduced seed yield by up to 72%. These results confirm the findings of other studies (Baros et al. 2004; Zheljazkova et al. 2011) that demonstrated the ability of early planting to produce higher yields. Across all three growing seasons with varying planting dates, sunflowers planted in November and December consistently yielded higher seed yield, oil content and oil yield, with a linear decline in yield as planting dates were delayed. The decrease in yield may be attributed to a shorter time from planting to maturity, resulting in immature kernels, and stress experienced during the critical grain fill period (Andrade 1995). During the grain-filling period, the determination of oil yield, encompassing both oil content and seed components (number of set seeds and seed weight), partially overlapped, making the yield significantly susceptible to environmental conditions. Oil content varied between 46% (9 November 2018) and 36% (5 February 2020) across hybrids and planting dates. The lowest oil content was observed in the two latest planting dates (January and February), indicating that delayed planting can reduce oil content by 2% (10 January 2019) to 10% (21 January 2021) and 20% (February). These findings align with Leon et al. (2003) and Echarte et al. (2010), who found that delayed grain filling due to late planting leads to reduced oil concentration, primarily due to low air temperatures or indirectly due to low solar radiation. Izquierdo et al. (2008) also suggested that grain oil concentration in sunflowers is mainly determined by the amount of photosynthetically active radiation intercepted by each plant during the grain-filling period. Aguirrezábal et al. (2003) reported that cumulative intercepted radiation is the main determinant of oil concentration among sunflower hybrids in Argentina. Akkaya et al. (2019) proposed that a reduction in oil content at a late planting date might be attributed to a shorter vegetation period caused by high air temperatures and low rainfall prevailing during the vegetation process and seed filling.

Oil yield from the present study ranged from 1.37 t ha^–1 (18 December 2019) to 0.31 t ha^–1 (5 February 2020) on average. November and December plantings consistently produced the highest oil yield across all growing seasons, indicating that delayed planting in January reduced oil yield by 3% to 26% in the first and third growing seasons, respectively. If planting was delayed until February, the oil yield decreased by 77%. These findings are in line with studies by Izquierdo et al. (2008) and Echarte et al. (2010), who found that a reduction in intercepted solar radiation during the grain-filling period leads to lower grain weight and oil content in sunflower cultivars. Zheljazkova et al. (2011) reported equivalent results from dryland trials conducted in the Mississippi region, suggesting that an earlier planting date may result in better crop establishment and higher yield.

Our study detected significant differences among the tested sunflower hybrids in seed yield, oil content and oil yield throughout all three growing seasons (Table 5). Seed yield ranged from 1.86 t ha^–1 (LG 5678 CLP) in 2019/2020 to 2.50 t ha^–1 (PAN 7160 CLP) in 2020/2021. Oil content varied from 53.16% (SY 3970 CL) in 2018/2019 to 37.23% (P 65 LP 54) in 2020/21. Oil yield ranged from 0.74 t ha^–1 (AGSUN 5101 CLP) in 2019/2020 to 1.25 t ha^–1 (LG 5710) in the 2018/2019 growing season. Over the three growing seasons, P 65 LL 02 exhibited the highest mean seed yield (2.41 t ha^–1), SY 3970 CL had the highest mean oil content (51.05%), and LG 5710 recorded the highest mean oil yield (1.15 t ha^–1). The observed differences between the tested sunflower hybrids can be explained by variations in their genetic constituents, as reported by Ali et al. (2014) and Nasim et al. (2017). Zheljazkova et al. (2008) suggested that while seed oil concentration depends on the sunflower genotype, its expression may vary under different environments. Andrianasolo et al. (2014) concluded that oilseed crop yield is highly variable and can be affected by genetic, environmental and agronomic factors and their interactions.

Table 5: Seed yield, oil content and oil yield for 16 sunflower hybrids evaluated on three different planting dates over three growing seasons

Conclusion

Several factors, including the year, planting date, hybrid selection, and their interactions, considerably impact sunflower seed yield, oil content and oil yield. The optimal period for planting sunflowers in the North West region is November to December. Conversely, planting sunflowers in late January and early February is discouraged due to a substantial reduction in seed yield, oil content and oil yield. Moreover, any further delays in planting exacerbate these reductions. Late planting initially prompts vegetative growth, enhanced by higher air temperatures and sufficient rainfall during the early growth phase. However, this advantageous start is followed by a shorter flowering growth period and a subsequent drought phase characterised by cooler air temperatures and diminished incident solar radiation during post-anthesis. These environmental conditions negatively impact the dynamics of grain filling, culminating in reductions in both seed and oil yield, and oil content. In summary, the study underscores the importance of strategic planting timing for sunflowers in the North West region. The findings provide practical guidance, emphasising the need to avoid late planting, which can have detrimental effects on key agronomic parameters, ultimately influencing the overall productivity of sunflower crops.

Geolocation information

Potchefstroom: 26°44′09.9″ S, 27°04′31.9″ E

Conflict of interest

The authors report no potential conflict of interest.

Author contributions

Safiah Ma'ali was responsible for research concept, literature review, methodology, manuscript writing, data collection and analysis and data interpretation; Nicolene Cochrane conducted statistical analyses and edited the manuscript; William Makgoga and Jan Erasmus conducted fieldwork, such as planting and maintaining the trials, assisting in data collection, and providing practical support throughout the project.

Use of artificial intelligence tools

None of the contributing authors used artificial intelligence (AI) software, algorithms or machine learning models during the research process. Furthermore, none of the ideas, protocols, writings, data, results or sections of this submission were derived from or benefited from the application of artificial intelligence tools.

Acknowledgements

The authors thank the Oil and Protein Seeds Development Trust and the Agricultural Research Council (South Africa) for funding this project and the sunflower team at Grain Crops for their technical assistance.

Data availability

Data is available on request.