Effects of nitrogen and phosphorus fertilizers and cotyledon removal on establishment and growth of yeheb nut bush (Cordeauxia edulis Hemsl.) outside its natural habitat

Abstract

Yeheb nut bush (Cordeauxia edulis) is a multipurpose but endangered shrub native to arid south-Eastern Ethiopia and Central Somalia. Establishment of this species was studied in two sets of experiments during 2005 to 2007. In the first set of experiment, field establishment was conducted at Dire Dawa, Ethiopia, which is located 725 km north west of the natural habitat (Bokh). Nitrogen at 0, 46 and 92 level and phosphorus at 0, 4 and 8 kg ha-1 were applied 84 days after transplanting. Application of 92 N/8 P kg ha-1increased seedling height by 134%; 46 N/4 P kg ha- 1 increased leaf area by 152% and dry weight of seedlings increased by 309% at 46/8 kg ha-1 NP compared to the unfertilized plants. Nitrogen and phosphorus fertilizers significantly altered soil as well as plant tissue N and P contents. Leaf and root N was significantly highest at 46 and 92 N kg ha-1, respectively while leaf P was maximised at 8P kg ha-1. In the second set, the impact of cotyledon removal was assessed in the greenhouse, Haramaya University by excision of cotyledon at 7 days interval for ten consecutive weeks and leaving the cotyledon with plant as a control. Removing cotyledon at 7, 14 and 35 days after germination (DAG) significantly reduced most of the growth parameters while seedlings with intact cotyledon had the highest dry matter accumulated. Thus, 46 to 92 kg N and 8 kg P ha-1 would help the establishment and growth of C. edulis in the field and seedlings should retain cotyledon during early establishment. However, more rates of N and P as well as methods and frequency of applications deserve further investigation. Key words: Cordeauxia edulis, cotyledon, Ethiopia, nitrogen and phosphorus fertilizers, seedling establishment.