Watermelon [Citrullus lanatus (Thumb) Matsun and Nakai ] is an important cash crop in West Africa where it is cultivated under rainfed conditions. The objective of this work was to identify best cultural practices for production of watermelons in the Sahel on stored rainwater in acid sandy soils. The experiments were carried out at the ICRISAT Sadore research center in Niger during two consecutive dry seasons, 2003 - 2004 and 2004 - 2005. Three soil management treatments were applied: micro-catchments (also called half-moons), planting pits (also called zaï) and sowing on flat land. Each of these three treatments came with and without a soil amendment comprising of 500 g of manure mixed with 24 g of a complete (NPK) fertilizer (15-15-15) individually applied to each planting hill. Two watermelon cultivars were tested: ‘Malali’ and ‘Kaolack’. In each of the two years the experiments were sown on the 1st and on the 21st of September. Fruit and biomass yield, fruit Total Soluble Solids (TSS), days to fruiting and harvesting were determined. Soil fertility, root development and other physiological parameters were monitored to explain some of the differences between treatments. Soil amendments increased marketable yields from 1.3 to 3.5 tons ha-1 on average. Marketable yields at the first planting date were double the yields of the second planting date (3.2 vs. 1.6 tons ha-1). Yield differences were due to changes in fruit number not in fruit weight. Deep placement of soil amendments resulted in significant root development in deeper soil layers. Highest watermelon yields were achieved when sowing the Malali cultivar in amended planting pits on September 1st giving a yield of 8.2 tons ha-1.
Key words: Citrullus lanatus, Malali, Kaolack, Zaï, planting pits, half moons, stored water, root development, Sahel.
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