Second-crop N fertilization improves lowbush blueberry (Vaccinium angustifolium Ait.) production

Penney, B. G., McRae, K. B. and Bishop, G. A. 2003. Second-crop N fertilization improves lowbush blueberry (Vaccinium angustifolium Ait.) production. Can. J. Plant Sci. 83: 149-155. Most commercial blueberry growers follow a 2-yr pruning cycle because second-crop yield in a 3-yr cycle is usually too low for an economical harvest. Research was conducted to determine the extent to which second-crop production could be increased by applying fertilizer in the second-crop year. Treatments, consisting of factorial combinations of N (0, 60 kg ha(-1)), P (0, 26 kg ha(-1)), and K (0, 50 kg ha-1), were studied over two 3-yr burn-pruning cycles on a natural lowbush blueberry stand. Treatments were applied prior to, or shortly after, flower buds started to swell in the spring of the second-crop year. Nitrogen increased ripe fruit yield by 65% (3410 vs. 2070 kg ha(-1)) when compared with plots not previously fertilized with N, and by 43% (3410 vs. 2380 kg ha(-1)) when compared with plots previously fertilized with N. These results indicate that N might make the second crop economical to harvest. Phosphorus did not significantly affect yield, but K applied in combination with N in the second-crop year negatively affected production and Mg uptake. The increase in yield by N was due to more ripe berries resulting from a higher total (ripe + unripe) number of berries and hastened maturity that increased the percentage of ripe fruit. Reduced fruit abortion is suspected to be the reason for higher berry numbers. In contrast, the negative response to K applications with N was due to reduced total berry numbers.