Sunflower (Helianthus annuus) originates from central and north America. Lately its importance as an oil crop has grown and at present it is tile second most important oil crop next to soybean. Total annual world production is some 20.9 million tons of seed from some 18 million ha.(FAOSTAT, 2001).
Sunflower thrives in climates ranging from arid under irrigation to temperate under rainfed conditions, but is susceptible to frost. Mean daily temperatures for good growth are between 18 and 25°C. The total growing period varies from 70 days in parts of Russia where the season is short to 200 days at higher altitudes in Mexico. In the subtropics under irrigation the total growing period is about 130 days. For temperate climates the optimum planting date for early as well as late maturing varieties is between late spring and early summer. Delay in planting results in shortening of the vegetative period and early maturity, causing a decrease in head diameter and seed weight. Sunflower is a short-day plant with a variable response to daylength, but day-neutral varieties exist.
The crop is mainly grown under rainfed conditions on a wide range of soils. Under erratic and low rainfall, a rather deep soil with good water holding capacity is required. Due to its deep root system (2 to 3m) soil water can be explored at great depths. Optimum soil pH is in the range of 6.0 to 7.5, but at lower values liming may be necessary. Fertilizer application is in general 50 to 100 kg/ha N, 20 to 45 kg/ha P and 60 to 125 kg/ha K. The crop is particularly sensitive to boron deficiency.
Optimum plant density is about 60 000 plants/ha with row spacing of about 0.9 m; seed rate is between 4 and 10 kg/ha. Both transplantation and direct seeding are practised.
In the major sunflower growing areas salinity problems are minor; an indication of tolerance to salinity during crop establishment is shown by the emergence percentage of seedlings which is 80 to 100% at ECe 0.70 to 75% at 4.5, 30 to 60% at 9.5, 15 to 55% at 10 and 0 to 25% at ECe 13 mmhos/cm. However, in later growth periods sunflower is moderately tolerant to salinity.
Stages of Development
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Stage length, days
Depletion Coefficient, p
Root Depth, m
Crop Coefficient, Kc
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1The lower values are for rainfed crops having less dense plant population