|Machado, Rui - UNIVERSITY OF EVORA|
Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: March 9, 2009
Publication Date: August 15, 2010
Citation: Bryla, D.R., Machado, R., Shireman, A.D. 2010. Effects of method and level of nitrogen fertilizer application on soil pH, electrical conductivity, and availability of ammonium and nitrate in blueberry. Acta Horticulturae. 868:95-101. Interpretive Summary: Most blueberry fields are irrigated by sprinklers or drip. While both are effective for commercial production, one major advantage of drip is the capability to apply water-soluble fertilizers during irrigation. This procedure, otherwise known as fertigation, can apply fertilizer very uniformly throughout a field and directly to the roots in small amounts as needed. Liquid fertilizer is usually injected from April to mid August with fertigation. Granular fertilizer, on the other hand, is commonly used with sprinklers and is usually applied in two or three large doses each spring. We did a study to compare fertigation to granular fertilizer application and determined the effects of each practice on N availability in a newly planted field of highbush blueberry. We found that N application by either method reduced soil pH, but granular fertilizer resulted in large peaks in soil ammonium concentrations after each application and much higher salt concentrations than liquid fertilizer applied gradually by fertigation. Higher salts damaged the roots of the young plants and reduced overall growth. Granular fertilizer also resulted in higher soil nitrate concentrations than fertigation, and since nitrate is not readily used by blueberry, more of it may be leached from the soil during rainy winter months.
Technical Abstract: Blueberries (Vaccinium spp.) require low soil pH and prefer N primarily as ammonium for optimum production. Nitrogen fertilizer methods and rates were evaluated in a new field of ‘Bluecrop’ blueberry (Vaccinium corymbosum L.) to determine their effects on soil pH and availability of ammonium and nitrate in soil solution. Treatments included four application methods (split fertigation, continuous fertigation, and two non-fertigated controls) and four rates of N application (0, 50, 100, and 150 kg/ha N). Fertigation treatments were irrigated by drip and injected with liquid urea fertilizer; split fertigation was applied as a triple-split from April to June while continuous fertigation was applied weekly from leaf emergence to approximately 2 months prior to the end of the growing season. Non-fertigated controls were fertilized with a triple-split of granular ammonium sulfate and irrigated by drip or microsprays. Soil pH was usually lower with microsprays than with drip, even when no N fertilizer was applied; however, soil pH was also reduced with higher N applications and, in fact, was similar between continuous fertigation and granular fertilizer (microspray) treatments when 150 kg/ha N was added. Nitrogen application with granular fertilizer, whether irrigated by microspray or drip, maintained much higher ammonium concentrations than continuous or split fertigation but often increased electrical conductivity (salinity) of the soil solution (ECw) to >2 dS/m. By comparison, ECw was always <1.5 dS/m with either fertigation method. Granular N application coupled with microsprays also resulted in higher nitrate concentrations than any other treatment, which may lead to more N leaching since the ability of blueberry to acquire nitrate-N is limited.