Watermelon (Citrullus vulgaris) is native to the dry areas in tropical and sub-tropical Africa south of the equator. The crop can survive the desert climate when groundwater is available and the fruit sometimes serves as a source of water for human consumption. World production is about 77.5 million tons fruit from 3.1 million ha.(FAOSTAT, 2001).
The crop prefers a hot, dry climate with mean daily temperatures of 22 to 30°C. Maximum and minimum temperatures for growth are about 35 and 18°C respectively. The optimum soil temperature for root growth is in the range of 20 to 35°C. Fruits grown under hot, dry conditions have a high sugar content of 11 percent in comparison to 8 percent under cool, humid conditions. The crop is very sensitive to frost. The length of the total growing period ranges from 80 to 110 days, depending on climate.
The crop prefers a sandy loam soil texture with pH of 5.8 to 7.2. Cultivation in heavy textured soils results in a slower crop development and cracked fruits. For high production fertilizer requirements are 80 to 100 kg/ha N, 25 to 60 kg/ha P and 35 to 80 kg/ha K.
The crop is moderately sensitive to salinity. Yield decrease due to salinity appears to be similar to that of cucumber, or: 0% at ECe 2.5 mmhos/cm, 10% at 3.3, 25% at 4.4, 50% at 6.3 and 100% at ECe 10 mmho s / cm .
Watermelon is normally seeded directly in the fields. Thinning is practised 15 to 25 days after sowing. Spacing between plants and rows varies from 0.6 x 0.9 to 1.8 x 2.4 m. Seeds are sometimes placed on hills spaced 1.8 x 2.4m. In areas prone to frost, sowing time is dictated often by the occurrence of frost; sometimes black plastic mulch is used for frost protection.
The graph below depicts the crop stages of watermelon, and the table summarises the main crop coefficients used for water management.
Near East (desert)
Depletion Coefficient, p
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Root Depth, m
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