Growth response of Grevillea robusta A. Cunn. seedlings to phosphorus fertilization in acid soils from Kenya
1999
Karanja, N.K. (University of Nairobi (Kenya). Soil Science Department) | Mwendwa, K.A. | Zapata, F.
Three experiments were conducted to assess the response of Grevillea robusta to phosphorus fertilization using acid soils showing low P levels from Eastern (Gituamba-Andosols) and Western (Kakamega-Acrisols) Kenya. In the first experiment P was applied as Minjingu phosphate rock (MPR- 13/P) at 0, 52 and 77 kg P per ha into 5 kg of soil. In the second experiment 2 g vesicular arbuscular mycorrhizae (VAM) soil + root inoculum per 5 kg soil was included in addition to the same MPR rates using Kakamega soil only. In the third experiment, MPR and triple superphosphate (TSP) were added to 5 kg Kakamega soil at a rate of 25.8 mg P per kg soil, and 32P isotope dilution techniques were used to assess P uptake in the shoot harvested at 3 and 6 MAT (months after transplanting). Application of MPR to the Andosol reduced height and root collar diameter of G. robusta significantly (p .05) as compared to the control. Significant increases (p .05) in height and root collar diameter where P was added compared to control were recorded with the Acrisol. Soil interaction with P fertilizer rates was highly significant (p .001) for both height and root collar diameter growth. The roots were not infected with VAM upon harvesting at 12 months. At 3 MAT the percentage P derived from the MPR and TSP was 3/ and 6/ respectively. P uptake decreased significantly (p .05) between 3 and 6 months. The results indicated that addition of P fertilizer in the Acrisols was probably required at the early stages of G. robusta growth but further research and particularly root studies are required to ascertain the above observations.
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