Location: Horticultural Crops Research UnitTitle: Growth and fruit production of highbush blueberry fertilized with ammonium sulfate and urea applied by fertigation or as granular fertilizer
|VARGAS, OSCAR - OREGON STATE UNIVERSITY|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2015
Publication Date: 3/30/2015
Citation: Vargas, O., Bryla, D.R. 2015. Growth and fruit production of highbush blueberry fertilized with ammonium sulfate and urea applied by fertigation or as granular fertilizer. HortScience. 50(3):479-485.
Interpretive Summary: Current nutrient management guidelines for blueberry were developed based on granular fertilizers and may not be optimized for plants fertilized by fertigation. Previously, we compared granular applications of nitrogen (N) fertilizer to fertigation in a new planting of highbush blueberry and determined that fertigation was less efficient (i.e., less plant growth per unit of N applied) but safer (i.e., less salt damage and plant death) than granular fertilizer during the first 2 years of establishment. The objective of the present study was to extend this original study and compare the effects of granular fertilizer to fertigation during the first 5 years of fruit production (year 3-7). Both application methods were evaluated using ammonium sulfate or urea. Fertigation resulted in more yield each year than granular applications of N fertilizer. Depending on treatment, yields ranged from 2-4 t/ha (1-2 ton/acre) during the first year of fruit production and increased to 14-20 t/ha (6-9 ton/acre) by the fifth year. The plants required 67-93 kg/ha (60-80 lb/acre) of N per year to optimize fruit production (whether N was applied by fertigation or as granular fertilizer), which is about 30-40% less than what is currently recommended for highbush blueberry.
Technical Abstract: The application of granular sources of nitrogen (N) fertilizers, including ammonium sulfate and urea, were compared to fertigation with liquid forms of the fertilizers in northern highbush blueberry during the first 5 years of fruit production. The granular fertilizers were banded on each side of the plant row in three equal applications per month from mid-April to mid-June. The liquid fertilizers were injected through a drip system in equal weekly applications from mid-April to early-August. Each fertilizer was applied at three N rates (increased as the plants matured), including 63-93, 133-187, and 200-280 kg/ha N, and compared to control treatments without N. Yield was 12% to 40% greater with fertigation than with granular fertilizer each year, and also greater with ammonium sulfate than with urea during the fourth year. Berry weight varied among treatments from year to year, but the weighted means, averaged over the 5 years, was 4% greater with granular fertilizer than with fertigation. Berry weight also decreased by 4-7% with higher N rates (200-250 kg/ha) during the first 3 years of fruit production. Leaf N concentrations were greater with fertigation in 4 out of 5 years, and greater with ammonium sulfate than with urea each year. Soil pH decreased with increasing N rates and was lower with granular fertilizer than with fertigation in 3 out of 4 years and lower with ammonium sulfate than with urea in 4 out 5 years. Overall, cumulative yields in each treatment averaged 32-63 t/ha over the first 5 years of fruit production and was greatest when plants were fertigated with ammonium sulfate or urea at rates of at least 63-93 kg/ha N per year.