EFFECTS OF NITROGEN, PHOSPHORUS AND POTASSIUM ON THE EARLY GROWTH OF <em>PINUS</em> <em>PATULA</em> AND <em>EUCALYPTUS</em> <em>GRANDIS</em>

Abstract

GOTORE T, MUREPA R & GAPARE WJ. 2014. Effects of nitrogen, phosphorus and potassium on the early growth of Pinus patula and Eucalyptus grandis. Effects of various levels of nitrogen (N), phosphorus (P) and potassium (K) applied singly or in combination on Pinus patula and Eucalyptus grandis tree growth in Zimbabwe were studied. Data were available from eight trials located in areas representative of the commercial forestry areas of Zimbabwe and characterised by varied rainfall patterns, ranging from 750 to 1524 mm per annum. Pinus patula growth responses to N fertilisation were small and variable and in some cases caused significant reduction in tree growth. Phosphorus effect showed mixed results, with a positive effect on P. patula growth at Nyangui North and Mtao Forests and none at Nyangui South and Charter North. Potassium fertiliser application had no effect on P. patula tree growth. The interactions between N and P, N and K, P and K as well as N, P and K were all not significant for P. patula growth at all sites. Eucalyptus grandis growth was not significantly influenced by N fertiliser application. Trees applied with P had negative response while tree growth was positive to K application at the site with sandy soil texture. Conversely, E. grandis tree growth responded positively to P and K fertiliser interactions at the same site. Tree growth responses to N × P × K factorial combinations were only significant (p < 0.05) for tree growth at two of four sites. Our results suggested that nutrition was not a major limitation to initial tree growth in provisional silvicultural zones I and III.