Response of Highbush Blueberry to Nitrogen Fertilizer during Field Establishment-II. Plant Nutrient Requirements in Relation to Nitrogen Fertilizer Supply

A study was done to determine the macro- and micronutrient requirements of young northern highbush blueberry plants (Vaccinium corymbosum L. 'Bluecrop') during the first 2 years of establishment and to examine how these requirements were affected by the amount of nitrogen (N) fertilizer applied. The plants were spaced 1.2 x 3.0 m apart and fertilized with 0, 50, or 100 kg.ha(-1) of N, 35 kg.ha(-1) of phosphorus (P), and 66 kg.ha(-1) of potassium (K) each spring. A light fruit crop was harvested during the second year after planting. Plants were excavated and parts sampled for complete nutrient analysis at six key stages of development, from leaf budbreak after planting to fruit harvest the next year. The concentration of several nutrients in the leaves, including N, P, calcium (Ca), sulfur (S), and manganese (Mn), increased with N fertilizer application, whereas leaf boron (B) concentration decreased. In most cases, the concentration of nutrients was within or above the range considered normal for mature blueberry plants, although leaf N was below normal in plants grown without fertilizer in Year 1, and leaf B was below normal in plants fertilized with 50 or 100 kg.ha(-1) N in Year 2. Plants fertilized with 50 kg.ha(-1) N were largest, producing 22% to 32% more dry weight (DW) the first season and 78% to 90% more DW the second season than unfertilized plants or plants fertilized with 100 kg.ha(-1) N. Most DW accumulated in new shoots, leaves, and roots in both years as well as in fruit the second year. New shoot and leaf DW was much greater each year when plants were fertilized with 50 or 100 kg.ha(-1) N, whereas root DW was only greater at fruit harvest and only when 50 kg.ha(-1) N was applied. Application of 50 kg.ha(-1) N also increased DW of woody stems by fruit harvest, but neither 50 nor 100 kg.ha(-1) N had a significant effect on crown, flower, or fruit DW. Depending on treatment, plants lost 16% to 29% of total biomass at leaf abscission, 3% to 16% when pruned in winter, and 13% to 32% at fruit harvest. The content of most nutrients in the plant followed the same patterns of accumulation and loss as plant DW. However, unlike DW, magnesium (Mg), iron (Fe), and zinc (Zn) content in new shoots and leaves was similar among N treatments the first year, and N fertilizer increased N and S content in woody stems much earlier than it increased biomass of the stems. Likewise, N, P, S, and Zn content in the crown were greater at times when N fertilizer was applied, whereas K and Ca content were sometimes lower. Overall, plants fertilized with 50 kg.ha(-1) N produced the most growth and, from planting to first fruit harvest, required 34.8 kg.ha(-1) N, 2.3 kg.ha(-1) P, 12.5 kg.ha(-1) K, 8.4 kg.ha(-1) Ca, 3.8 kg.ha(-1) Mg, 5.9 S, 295 g.ha(-1) Fe, 40 B, 23 g.ha(-1) copper (Cu), 1273 g.ha(-1) Mn, and 65 g.ha(-1) Zn. Thus, of the total amount of fertilizer applied over 2 years, only 21% of the N, 3% of the P, and 9% of the K were used by plants during establishment.