Rock Phosphate and Varietal Effects on Growth and Yield of Kenaf.

  Field trials were conducted at Ibadan, Nigeria to evaluate the effects of Ogun rock phosphate (ORP) amended with an organic waste and urea on growth and seed yield of two varieties of Kenaf (Cuba 108 and Tainung 1). Use of Ogun rock phosphate as a phosphorus source was compared with NPK 20-10-10. Performance with a mixture of   ORP + cowdung; ORP + compost; ORP + poultry manure and ORP + Urea were also assessed, compared with a no fertilizer control treatment. Results showed that P application significantly increased Kenaf plant height and seed yield. NPK - treated plants were significantly taller than the unfertilized plants. However, plants treated with amended ORP had comparable heights among the three organic sources and with NPK fertilization.  With Cuba 108, plant heights ranged from 240 – 280 cm in 2006 and from 218 – 239 cm in 2007 with the fertilized plants, when the unfertilized plants were 224 and 213 cm tall. The Tainum 1 Kenaf plants were between 233 and 252 cm tall in 2006 and between 220 and 238 cm tall in 2007 with the fertilized plants, when the unfertilized plants were 230 and 215 cm tall. Seed yield with Cuba 108 ranged from 940 – 1440 kg ha-1 in 2006 and from 500 – 700 kg ha-1 in 2007, with the fertilized plants, when the unfertilized plants yielded 784 and 473 kg ha-1 in 2006 and 2007, respectively. Yields from Tainum 1 were between 796 and 1077 kg ha-1 in 2006 and between 584 and 691 kg ha-1 in 2007 with the fertilized plants, when yields from the unfertilized plants were 726 and 522 kg ha-1 in 2006 and 2007 respectively. NPK fertilization gave the highest seed yields with the two varieties in both years.  The highest relative agronomic efficiency (RAE) value of 87 and 48 % relative to mineral fertilizer (100 %) were obtained by plants treated with ORP + CP for Cuba 108 and Tainung 1 respectively, in 2006. In 2007, the highest RAE value of 89% was obtained by the plants treated with ORP + PM for Cuba 108 and 95% with ORP + Urea for Tainung 1. NPK - treated soil had the highest soil available P. Ogun Rock Phosphate application is comparably effective as NPK 20-10-10 when applied, complemented with organic manures and urea for kenaf production.