Abstract:
Three trials to study the effects of N and P rates on growth, yield and seed oil content of four castor varieties were conducted during the rainy seasons of 2006 – 2008 on the research farm of the Institute for Agricultural Research, A.B.U Samaru Zaria,(110 11‟ N, 070 38E, and 686m above sea level). The treatments, which consisted of three levels of N (0,60 and 120 kg/ha), three levels of P (0, 7.92 and 15.84 kg/ha) and four castor cultivars (Ex-Brazil 1, Ex-Brazil 2, Ex-India 1 and Ex-India 2) were laid out in split plot design with a factorial combination of N and P levels allocated to the main plots, while the four varieties were assigned to the subplots. The treatments were replicated three times. The results revealed that application of 120 kg N/ha and 15.84 kg P/ha produced significantly higher growth, yield, and seed oil content compared with the two lower N and P rates. Ex-Brazil – 1 (a big seeded variety) produced the best yield, growth and yield parameters while Ex-Brazil – 2 (a small seeded variety) produced the highest seed oil content, indicating that the Brazilian varieties were better adapted to Northern Guinea Savanna ecological zone compared with their Indian varieties. Ex-India – 2 was the least adapted variety. The two big seeded varieties (Ex-Brazil – 1 and Ex-India – 2) had the highest height-to-first-capsule and capsule diameter and more S and Na content of leaves. The small seeded varieties (Ex-Brazil – 2 and Ex-India – 1) had the highest number of days to 50% first flowering, higher plant count at harvest and higher Ca, N, P, K and seed oil content. Significant interactions between the treatments were observed with most of the yield and growth characters. Correlation analysis revealed that in 2006, a positive and significant correlation between seed yield/ha and days to 50% first flowering and also with length of raceme/plant, while in 2007 it was positive and significant with number of racemes/plant and also with number of capsules/raceme. Similarly in 2008, there was a positive and significant correlation between seed yield/ha with days to 50% first flowering, LAI at 16 WAS, capsule weight/plant, CGR at 16 WAS, diameter of capsule and length of raceme/plant. In the combined analysis however, a positive and significant correlation existed between seed yield/ha and length of raceme/plant, diameter of capsules, days to 50% first flowering, number of racemes/plant, capsule weight/plant and number of capsules/raceme. Coefficient analysis revealed that the direct and indirect effects of growth characters on yield was more through plant height in 2006 and combined analysis. Coefficient analysis also revealed that the direct and indirect effects and also the percent contribution of some growth and yield components on seed yield were highest through seed oil content. The combination of oil content and number of racemes/plant in 2006, and oil content with raceme length/plant in 2007, 2008 and the combined mean made the highest contribution to yield. From the result obtained in this study, it can be concluded that application of 120 kg N/ha and 15.84 kg P/ha on the Brazilian varieties which resulted in highest growth, yield and seed oil content can be adopted by castor farmers in the Northern Guinea Savanna agro-ecological zone of Nigeria.
EFFECTS OF NITROGEN AND PHOSPHORUS RATES ON GROWTH, YIELD AND OIL CUNTENT OF FOUR VARIETIES OF CASTOR (Ricinus communis L.)
