Studies on the response of ‘Tifblue’ and ‘Woodard’ rabbiteye blueberries to fertilizers

Abstract

A 6-year field study was conducted to compare the effects of 11 N-P-K fertilizer formulations and five N sources applied to two rabbiteye blueberry (Vaccinium ashei Reade) cultivars. Fertilizers containing only ammonium nitrate (AMMN) and double rates of AMMN reduced ‘Tifblue’ yields during the first three production years when compared to no fertilizer applied. Each of the fertilizers, azalea-camellia (A-C), commercial grade 5-10-10 (COMM), and cottonseed meal (CSM), increased ‘Tifblue’ yields over the control group beginning the sixth year in the field. Various fertilizers applied did not improve ‘Woodard’ yields throughout the 6-year experimental period. At plant age 8, fertilizer formulations 1-0-0 and 2-1-1 (oxide basis) caused significant yield reduction. Fertilizer formulations did not influence fruit size of either ‘Tifblue’ or ‘Woodward’ significantly over the 6-year period. N-P-K fertilizers 1-1-1 and 2-2-2, A-C and COMM increased growth of 7-year-old ‘Tifblue’ plants. AMMN, A-C, COMM, and CSM enhanced ‘Tifblue’ foliage color score. However, only A-C improved the color of ‘Woodard’. N sources AMMN, ureaform (URAM), and urea (UREA) in fertilizer formulations containing N decreased yield on 4- and 5-year-old ‘Tifblue’ and ‘Woodard’ plants, but AMMN increased ‘Tifblue’ yield on 7-year-old plants. Fertilizing ‘Tifblue’ with A-C, COMM, or CSM would increase return from fruit sale by $3080·ha⁻¹, but applying 1-0-0 or 2-1-1 would decrease grower's profit by 40 to 60%. There was no yield or dollar return benefit from fertilizing ‘Woodard’ plants grown on a virgin acidic soil, but there was an indication (statistically non-significant0 of increased yields with potassium sulfate, A-C, COMM, and CSM after seven years of age. These results indicated that: (1) blueberry response to fertilizers varied from year-to-year, (2) genetic differences exist among blueberry cultivars in response to type of fertilizer applied, (3) rabbiteye blueberry plants do not benefit from high oxide base levels of available N in an N-P-K fertilizer, and (4) fertilizer requirements of rabbiteye blueberry plants need to be evaluated over an extended period of time to obtain a reliable response.