Herbicidal weed control and crop-year NPK fertilization improves lowbush blueberry (Vaccinium angustifolium Ait.) production

Past research has shown that fertilizer applied in the vegetative year can increase yield, but not always. Fertilizer applied in the crop year without weed control also has been shown to increase yield. The present study, con ducted on a natural lowbush blueberry stand for 8 yr, compared the effects of factorial combinations of two rates each of N (0, 60), P (0, 26), and K (0, 50 kg ha(-1)) applied either in the vegetative or crop year, with or wi thout weed control. Greatest production was obtained with weed control, whi ch increased ripe fruit yield by 247% over that from plots without weed con trol. Nitrogen alone or P and K with N also increased yield, but only when applied in the crop year to weed-controlled plots. Phosphorous or K alone w as of little benefit. Nitrogen increased ripe fruit yield from 3910 (unfert ilized plots with weed control) to 4440 kg ha(-1) and in combination with P and K to 5520 kg ha(-1). Yield increases from weed control and N were due to increased berry weight and hastened maturity, but weed control also incr eased total berry number. The increase by P and K was due to an increase in total and ripe berry numbers. Nitrogen applied in the vegetative year, alt hough producing more flower buds m(-2) than when applied in the crop year, gave lower yields. Fruit abortion, due to insufficient nutrients in the cro p year, particularly N, is suspected to be the reason for the reduced yield .