| The effect of planting density and nitrogen (N) fertilization on growth, yield, and N partitioning in young and mature 'Bluecrop' blueberry plants was studied over a two year period. Depleted 15N-ammonium sulfate was applied at different rates and on different dates in a mature planting, and at different rates in a young, newly established planting during the first year of study (2002). Non-labeled fertilizer was applied the second year (2003). Three rates of N fertilizer (0, 100, and 200 kg·ha-1 of N) in combination with two in-row spacing treatments (0.45 m and 1.2 m) were studied in the mature planting. In addition, three different dates of application of labeled fertilizer at the same rate was also tested. Nitrogen fertilization rate and spacing did affect the total amount of fertilizer- 15N present in each part, but percent partitioning of 15N was only affected by plant part. Plants at 1.2 m had a higher percentage of 15N partitioned to the crown and three-year and older wood, but reduced partitioning to large roots than plants at 0.45 m. Application date had a large effect on the total amount of NDFF recovered in the plant at the end of the first season. Application of N fertilizer in either April or May resulted in five times more NDFF in the plant than fertilizer application in July. Percent partitioning of NDFF was also affected by application date. Late fertilization resulted in labeled N allocated mainly to small roots, leaves and shoots, whereas spring-applied fertilizer was allocated mainly to leaves and fruits. In the new planting, established using two-year-old plants, N fertilization rate affected plant dry weight, total N content, percent NDFF, and fertilizer recovery. By October, plants fertilized with 50 kg·ha-1 of N had the largest dry weight and N accumulation. Ammonium toxicity was observed in plants fertilized with 100 and 150 kg·ha-1 of N. Percent NDFF was 60% and 67% for the 50 and 100 kg·ha -1 of N, respectively. Fertilizer recovery reached a maximum of 10 to 17% in October, depending on N fertilization rate.(Abstract shortened by UMI.)... |
