Fertilizer combinations benefit diameter growth of plantation black walnut

The diameter at breast height (dbh) growth of black walnut (Juglans nigra L.) trees in an 18-year-old plantation was measured over 4 years to determine the effect of nitrogen (N) and potassium (K) fertilization separately, in combination, and with and without phosphorus (P), broadcast annually at two rates. Trees in treatments containing N had significantly better dbh growth than trees in other treatments. However, doubling the application rate of 310 kg ha(-1) of N and P and 490 kg ha(-1) of K had no significant effect on dbh growth. There was a positive significant correlation for leaf N and dbh growth. The significant negative correlation between leaf P and dbh growth suggests that soil P concentrations may be less than the amount needed for accelerated dbh growth.