• MATERIAL AND METHODS
• Site and soil
• Layout and experimental design
• Treatments
• Crop husbandry
• Data recording
• Statistical analysis
• RESULTS
• DISCUSSION

Pakistan has continual deficiency in edible oilseed production and is the third largest importer of edible oil in the world involving a huge foreign exchange. The imports of vegetable oils are in an ever increasing quantity imposing a severe drain on national economy. The import bill of edible oil was about Rs. 77.78 billion during 2009-10 (July-March) (Govt. of Pakistan, 2009-10). Therefore, concerted efforts are needed to enhance oilseed production to minimize the gap between its production and consumption. Sunflower is a high yielding non-traditional oilseed crop and has the potential to shrink the gap existing between consumption and domestic production of edible oil (Hussain et al., 2010; Ehsanullah et al., 2011a). Nonetheless, it is a short duration crop (90-120 days) and can be grown twice a year. It fits well in existing cropping system and can be grown without replacing any major crop (Hussain et al., 2008).

The average yield of sunflower in Pakistan is lower compared with the potential of the hybrids. The shortfalls in the crop management are mainly responsible for this gap between potential and average yield of sunflower. Two important management factors responsible for limiting sunflower yields in Pakistan include the improper irrigation and planting methods (Erdem et al., 2001; Shivakumar et al., 2001). Planting geometry affects both plant growth and development by balancing the interplant competition (Malik et al., 1992; Malik et al., 2001; Ehsanullah et al., 2007). Planting geometry determines the distribution pattern of plants over a field; thereby it directly affects solar energy interception and evaporation and indirectly effects water use efficiency (Ghaffar et al., 2012). Narrow row spacing ensures more uniform distribution of plant over a given area and makes a plant canopy more effective in intercepting radiant energy and suppressing weeds (Saeed, 1994; Ehsanullah et al., 2011b; Farooq et al., 2011).

Irrigation at various growth and development stages greatly influences the crop growth and yield (Jana et al., 1982; Asbag et al., 2009). All the physiological processes of the plant are directly and indirectly influenced by water status of the plant. Water is essential for cell turgidity, which is related to photosynthesis, growth of cells, tissues and organs  (Reddi and Reddy, 1995). Water stress is considered to be the most important factor limiting the photosynthetic efficiency and yield of sunflower (Ribas-Carbo et al., 2005; Iqbal et al., 2005). Availability of adequate amount of moisture at critical stages of plant growth not only regulates the metabolic processes in plants but also increases the effectiveness of fertilizer applied to the crop (Akhtar et al., 1993). In conventional farming, sunflower is widely cultivated in flat fields with huge demand of irrigation water which is becoming a limiting natural resource day by day. Keeping in view these factors, the present work was conducted to study the influence of different irrigation management strategies on sunflower sown on flat surfaces and ridges.

MATERIAL AND METHODS

Site and soil

The study was conducted at student research farm, Department of Agronomy, University of Agriculture, Faisalabad (31.25oN, 73.09oE). The soil of experimental area was sandy clay loam in texture with 59% sand, 15% silt and 26% clay. Experimental soilbelonged to Lyallpur soil series i.e., aridisol-fine-silty, mixed, hyper-thermic Ustalfic,Haplarged in USDA classification & Haplic Yerrmosols in FAO Classification).

Layout and experimental design

The experiment was laid out in a split plot design and replicated three times. Net plot size was 3.6 m × 5 m. The buffer area of 1 m was kept to avoid the buffer effect of irrigation among different treatments. Planting methods and irrigation levels were randomized in main and sub-plots respectively.

Treatments

Two planting methods flat sowing of sunflower at 60 cm apart single rows (P₁) and ridge sowing at 60 cm apart single row (P₂) and three irrigation treatments i.e. I₀ (irrigation at early vegetative stage, at bud visible stage, at anthesis and at achene development stage), I₁ (irrigation at early vegetative stage, at bud visible stage and at achene development stage) and I₂ (irrigation at early vegetative stage, at bud visible stage and at anthesis stage). In I₁, irrigation was missing at anthesis and in I₂ irrigation was missing at achene development stage.

Crop husbandry

Experimental area was provided with a pre-soaking irrigation to prepare seedbed by cultivating soil three times followed by planking each time (Mead and Chan, 1988). For ridge sowing, ridges were made using tractor drawn ridge maker. Sunflower hybrid (Hysun-33) was sown on 24th February at a plant-plant distance of 25 cm using a seed rate of 8 kg ha^-1. Fertilizer was applied at 100 kg N and 90 kg P₂O₅ ha^-1 while half of N and full phosphorus were applied at sowing and remaining half N was applied with first irrigation (Craswell et al., 1981). Weather data during the course of study are given in Table 1.

Table 1. Mean monthly weather data during the course of study.

Data recording

Plants in each plot were noted to record the plant population per unit area. Plant height, number of achenes per head and head diameter were recorded from five randomly selected plants at maturity and averaged. One thousand achenes were counted from each plot to record 1000-achene weight using electric balance. The matured crop was harvested and allowed to sundry in the field for one week. Afterwards, sunflower bundles in each plot were weighed to record biological yield ha^-1 while achenes were separated from sunflower heads to record achene yield ha^-1. Oil contents were determined by nuclear magnetic resonance (NMR) 4000 (Newport Pagnell, England), in Seed Technology Laboratory, Directorate of Oilseeds, Ayub Agricultural Research Institute Faisalabad, Pakistan according to the method of Robertson and Marrison (1979).

Statistical analysis

Collected data were analyzed statistically by using the Fisher’s analysis of variance technique according to split plot design (Steel et al., 1997). Least significant difference test at 5% probability was used to compare the differences among treatments means. 

RESULTS

Planting methods and irrigation levels had considerable effect on sunflower productivity along with entire yield components (Table 2). Sunflower sown on ridges exhibited more plant height, number of achenes head^-1 and 1000- achene weight compared with the crop sown on flat seed surface (Table 2). Planting methods had non-significant effect on plant population and head diameter of sunflower (Table 2). Likewise, irrigation at all critical growth stages of sunflower resulted in maximum plant height, head diameter, number of achenes head^-1 and 1000-achene weight of sunflower; while water stress at anthesis stage by withholding irrigation results in declined plant height, head diameter, number of achenes head^-1 and 1000-avhene weight of sunflower (Table 2). Nonetheless, irrigation levels had insignificant effect on plant population at harvest (Table 2).

Table 2. Effect of planting methods and irrigation levels on different parameters of sunflower.

 Ridge planted sunflower harvested more achene yield along with elevated harvest index and achene oil contents than flat seed bed, while stalk and biological yield of sunflower remained unaffected by different planting methods (Table 2). Likewise, normal irrigation treatment harvested the maximum achene and biological yield of sunflower accompanied with elevated harvest index and achene oil contents (Table 2). Water stress at anthesis stage proved more detrimental with lowest achene and biological yield, harvest index and achene oil contents (Table 2). However, irrigation levels had insignificant effect on stalk yield of sunflower (Table 2).

The interactive effects of planting methods and irrigation levels were insignificant for all the data recorded except plant height and 1000-achene weight (Table 2). Irrigation at all the critical stages to the ridge sown sunflower exhibited the maximum plant height and 1000-achene weight followed by the flat sown sunflower with irrigation at all critical stages. Flat sowing of sunflower with irrigation missing at anthesis exhibited the lowest plant height and 1000-achene weight (Table 2).

DISCUSSION

Similar plant population for all the treatments was the result of same seed rate and plant-plant distance for both the sowing methods and the three irrigation levels (Rafiq et al., 1998; Jabran et al., 2010). The moisture stress at any critical growth stage may reduce the crop growth and plant height (Kakar and Soomro, 2001; Ali et al., 2009). Maximum plant height in ridge sown crop may be attributed to better utilization of moisture as compared to the flat sown crop (Abdullah et al., 2008). Head growth in sunflower is very sensitive to water stress; therefore, head diameter was less in the treatments where irrigation was missed (Takami et al., 1981). Missing irrigation at anthesis and at achene development stage greatly reduces the number of achenes per head especially when grown on flat seedbed (Kakar and Soomro, 2001). Akhtar et al. (1993) reported that if plants were given water stress at anthesis and seed setting, a significant decrease in number of achenes per head were resulted. Ravishankar at al. (1990) reported that water stress reduces the test weight in sunflower especially during the late stress. Maximum 1000-achene weight in I0 treatment may be attributed to more appropriate number and time of irrigation which resulted in better growth and development of sunflower crop and eventually increased 1000-achene weight (Buksh at al., 1999). Irrigation at budding has a great effect on accumulation of substantial biomass which resulted in better achene and biological yield (Connor et al., 1985). Stalk yield, achene yield and biological yield was significantly higher in ridge sown sunflower due to the better utilization of irrigation water to the root system. Achene yield and biological yield, in turn, resulted in significantly higher harvest index in sunflower irrigated with normal four irrigations. This significant difference in achene oil content may be attributed to the fact that water stress at anthesis and achene development stage decreased the achene oil content (Jana at al., 1982 and Rafiq at al., 1998).

It is concluded that for attaining maximum productivity of sunflower along with elevated oil contents, the crop should be sown on ridges and irrigated at all critical growth stages.

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