Growth and nutrients variation between Grevillea robusta provenances in Tanzania

Abstract

The growth and foliar nutrient content of Grevillea robusta provenances at two sites in Morogoro Tanzania were investigated. The two sites were located 70 km apart and differed in altitude, soil and rainfall. The best growth was recorded at Kiroka site where at the age of 2 years provenances attained a mean height of 6 m and diameter of 10 em. Growth was poorer at Mkundi where the mean height was 3 m and diameter of 4 em. Among the provenances, Manriver and Rapville provenances from Australia exhibited early superiority for height, diameter and disease resistance at both sites, while the Soni—Lushoto and Rombo land races had higher disease resistance at the drier Mkundi site. Foliar analysis results did not show significant provenance variation but nitrogen, phosphorus and potassium differed significantly between the two sites. Mean nitrogen, phosphorus and potassium concentration at Mkundi site were 1,38%, 0,047%, and 0,43%, respectively; while at Kiroka they were 1,65%, 0,061% and 0,55%, respectively. Nitrogen was also significantly correlated with root collar diameter, height and diameter to the first branch (r = 0,4). Both phosphorus and potassium were significantly but weakly correlated with height, branch diameter and height to the first branch. Only potassium was significantly but negatively correlated with forking (r = 0,25), and disease resistance (r = 0,33), and positively with root- collar diameter (r = 0,37). Regression analysis indicated that Nitrogen and Phosphorus explained a small proportion of variation in height (r² = 0,23), root -collar diameter (r² = 0,20) and branch diameter (r² = 0,32). These results have demonstrated considerable variation in growth between provenances but little provenance variation in nutrient composition. However, the effect of site difference was greater than the provenance effect.