SUMMARY
Growth responses and concentrations of mineral elements in leaves of ‘Tifblue’ rabbiteye blueberry were studied using water culture. In experiment 1, combinations of three N sources [(NH4)2SO4, NH4NO3, NaNO3] and four pH levels (average pH 3.5, 4.5, 5.5, 6.5) were evaluated. In general, top growth and root growth were superior with (NH4)2SO4 and NH4NO3, and inferior with NaNO3. Growth was best in the N source at pH combinations of NH4NO3 at pH 3.5-4.0, NH4NO3 at pH 4.1-5.0, and (NH4)2SO4 at pH 4.1-5.0, and poorest with NaNO3 at pH 6.1-7.0. However, growth with NaNO3 at pH 3.5-4.0 was the same as with (NH4)2SO4 at pH 6.1-7.0. In experiment 2, ten N sources, including their different elemental components, were evaluated. The top and root growth were superior with the NH4-N forms [NH4Cl, NH4H2PO4, (NH4)2SO4], and inferior with NO3-N forms [Ca(NO3)2-4H2O, KNO3]. Growth was intermediate with Mg(NO3)2-6H2O, NaNO3, NH4NO3, or a mixture of (NH4)2SO4 and NaNO3. The growth with NH2CONH2 (urea) was similar to that with NH4Cl. In experiment 3, three N sources [(NH4)2SO4, NH4NO3, NaNO3] were replaced with one of the alternative sources half way (at July 16) through the growing period. In general, the top and root growth were superior with (NH4)2SO4 and NH4NO3 applied during the first half of the growing period (from April 18 to July 16), whereas, growth with NaNO3 was inferior. Applying (NH4)2SO4 during the later half of the growing period (from July 17 to October 16) increased growth, while NaNO3 applied at this time decreased growth. A comparison of leaf mineral concentrations in the three experiments suggests N was highest when (NH4)2SO4 was the N source and lowest when NaNO3 was the N source. An imbalance between cations was observed. It is concluded that fertilizers containing the NH4-N form are essential for optimum growth of ‘Tifblue’ rabbiteye blueberry.
Key Words:
