Soils And Climate
- Whatever soil type is available, good drainage is more important than basic fertility, for it is usually easier to supply nutrients than improve drainage.
- Sunflower grows well on neutral to moderately alkaline soils, with a range of pH 6.5 – 8.0, but dislikes acid conditions.
- Wild varieties are tolerant of poor drainage but cultivated varieties are unsuited to such conditions, which increase susceptibility to fungal disease and lodging from lack of support.
- Salinity affects plant growth, development and some seed characteristics, usually oil content, and also influences nutrient uptake.
- Where salt concentrations are low to moderate, the first visual symptom is often a thin stem and stunted growth.
- Salinity can also reduce disease resistance, for example to Macrophominia in Tunisia and charcoal rots.
- Varietal differences to salinity are becoming increasingly reported, a very valuable characteristic, since the proportion of salt affected soils in the irrigated areas of the world continues to increase, and selection of varieties suited to these conditions is becoming more important.
- The use of micro elements in fertilizer mixtures can assist in increasing salt tolerance, for the growing of sunflower in these regions would add a valuable cash crop, or be an addition to local diets.
- There are indications that sunflower roots play an important role in the plant's tolerance of salinity, in that they may act as accumulators of sodium rather than as a barrier to its assimilation.
- In India, an exchangeable sodium percentage higher than 16 delayed germination, and later delayed the development of flower heads.
- Reduction in germination or emergence caused by salinity. Soils containing 0.2 per cent salts decreased yields by nearly 40 per cent.
- The depressing effect of high salinity levels on emergence is also related to temperature at this period, but there would also appear to be varietal differences in this response.
- Some cultivars are adversely affected by high soils temperatures some by low, while others emerge well at a high or low temperature, but poorly in the mid range.
- The degree of salinity also affects the rate of, and total emergence at different temperatures.
- It would thus appear that there is considerable scope for increasing salt tolerance in sunflower.
- Avoid acid, salime and ill-drained soils for sunflower cultivation.
- For rainfed sunflower heavy clays or clay loams are more suitable since they are highly water retentive.
- Deep soils always preferable at least 15-20 cm.
- To cultivate this crop in rabi season with residual moisture select only heavy soils.
- Light soils are well suited for this crop where irrigation is not a limiting factor.
- Day length influences time to flowering it does so in the period from emergence to budding.
- After this there was no apparent effect.
- However, for all practical purposes, sunflower can be considered day neutral, and within any large geographical area.
- Under controlled environmental conditions it has been shown that development was more rapid at 12 hours daylight equivalent than at 16 hours of longer.
- However, as noted, high temperature is more likely to reduce the time to maturity.
- Frost will damage sunflower to some degree at all sages of growth, although mature plants are more resistant to low temperature than soyabean or maize.
- Young plants in the four to six leaf stage can apparently withstand temperatures of 5 to 60C for short periods.
- However, a hard frost after floral initiation, about the eight leaf stage, will usually reduce yield by affecting head development, although visual damage, may appear slight.
- Frost will also damage immature seed and substantially reduce viability, but mature seed is less affected.
- This may be of little concern to commercial oilseed producers, but can influence the choice of site for seed production.
- A frost free period of about 120 days is recommended where sunflowers are to be grown on a commercial scale.
- Sunflower grown well within a temperature range of 20 - 250C, although controlled environment tests indicate that 27 - 280C would appear to be the optimum.
- A range of 8 - 340C is tolerated without significant yield reduction, indicating adaptation to regions with warm days and cold nights.
- A major visual effect of temperature is on the rate of development, with prolonged high temperature reducing the time to maturity, in some instances by nearly 50 per cent
- Temperature is known to affect seed oil content, seed and oil characteristics, but its effects on plants growing in the field are often masked or modified by other environmental factors.
- In general, temperature which remains above 250C at flowering is believed to reduce seed yield and seed oil content.
- As temperature during development decreased there was an increase in linoleic acid in the range 49 - 74 per cent.
- The contrary produced an increase in oleic acid content.
- The marked reduction in linoleic acid is believed to due to temperature acting on the desaturase enzymes, responsible for the conversion of oleic to linoleic acid.
- It may thus be necessary to relate time of sowing to temperature at flowering when a particular type of oil is required.
- The effect of temperature is not limited to its direct influence on seed oil constituents, since the basically different types of oil produced can directly influence local manufactures and their produce range.
- Sunflower is considered to be drought resistant and while this may be so, oil yield is substantially reduced if plants are allowed to become stressed during the main growth period and at flowering.
- A major symptom of moisture stress in the vegetative phase is a reduction in the number and size of leaves.
- Should a water shortage continue, lower leaves are shed and plant height will be substantially less than normal.
- One of the mechanisms employed by sunflower or resist moisture stress is by wilting, since it has been shown in controlled trials that in limp leaves water loss was reduced to a greater extent than photosynthesis.
- Plants can be independent of rainfall to a large extent, and good crops produced with as little as 500mm of irrigation water only, provided the subsoil moisture is adequate.
- Sunflower will produce a moderate yield on rainfall down to 300mm, but at this level of production is unlikely to be commercially viable as a mechanized crop.
- In the field, the relationship between low rainfall and seed yield is often almost linear from 200 to 500 mm, with 1t / ha usually achieved around 300 - 350mm.
- As a guide, the yield which can reasonably be expected from rain grown sunflower in more arid areas is approximately half that of a local sorghum crop.
- It should be noted, however, that in arid conditions seed oil content is adversely affected.
- Between 500 and 750 mm of rain, and some of this may be stored soil moisture, evenly spread over the growing period and ceasing just before main flowering and seed filling, will normally produce excellent crops.
- Losses from disease and lodging can be severe when rainfall is above, 1,000 mm unless the soil is free draining, especially if there are heavy falls when plants are fully grown.
- Various methods have been developed to assist growers to select suitable areas or soils.
- Because of their height, sunflower are susceptible to damage by high wind from when they are half grown, more so when irrigated as moist soil gives less support.
- There is considerable variation in the ability to resist wind damage basically related to root development, and this should influence selection when choosing varieties to be grown in windy locations.
- Hail can be extremely damaging to young seedlings which seldom recover if the terminal shoots are destroyed.
- Full grown or mature plants are little affected, even though leaves may appear shredded or badly holed.
- Based on the climate requirements discussed above sunflower can be grown throughout the year.
- However, the sowing time should be determined based on three aspects.
- There should not be moisture deficit between bud stage to flowering.
- The crop should not be caught in rains during pollination period
- Pollination period should not coincide with the period of high temperatures since the honey bee activity is negligible when high temperature are prevailed and thus poor seed setting.
- Hence, under Andhra Pradesh conditions sowings should not be done beyond 15th February.
- Sunflower Management