Sunflower Seed Yield And Root Development In Relation To Water And Nitrogen
Mugah, J O
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Kenya continues to spend large sums of the scarce foreign currency on the importation of vegetable oil. Adequate local supplies of sunflower would save the country such expenditure. Besides, the protein-rich cake obtained after extraction of oil would contribute towards the improvement of the nutritional quality of livestock feed. Vast areas of Kenya receive marginal rainfall and are therefore unsuitable for cultivation of a large number of cash crops. Sunflower is adaptable to these areas because it matures relatively faster and has a low water requirement. Successful cultivation of this crop in such areas will, however, require appropriately researched, site-specific information to guide farm practices. The objective of this study was, therefore, to contribute towards this need through determination of the rooting characteristics of sunflower in relation to water extraction under various water and nitrogen regimes, and generation of yield-water-nitrogen functions for sunflower. The study was conducted at two sites, one with a deep, well-drained Humic Nitosol (at Muguga) and the other with a shallower, saline-sodic soil (at Naivasha). Two irrigated experiments each lasting approximately four and a half months were conducted at every site: during the driest part of the year. A line-source sprinkler irrigation system was used to create differential moisture regimes. Nitrogen treatments were randomised at each "water level" perpendicular to the direction of the water gradient. Root-length density was estimated using Newman's line intersection method; seed yield was related to water and nitrogen using a quadratic model. Results show that roots grew to depths beyond 2 meters in adequately fertilized but moisture-deficient treatments and extracted significant. amount.s of water from these depths. Maximum seed yield of 2329 kg/ha was obtained with 90 kg N/ha and 445 mm of applied water at Muguga. The corresponding figures at Naivasha were 2284 kg/ha, 60 kg N/ha, and 438 mm. Seed yield was related to applied water and nitrogen through the model: Y=557+4.7W+9.89N-0.04W2-0.4NL+0.002NW at Muguga, and Y=488+4.1W+l0.3N-0.005W2-0.06N2+0.007NW at Naivasha.