Effects of Gypsum on Nutrient Uptake, Growth and Yield of the Wild Lowbush Blueberry

Gypsum (calcium sulfate) is an organic soil amendment that contributes Ca and S and displaces other cations from organic matter and clay particles making them available for plant uptake, without significantly altering soil pH. Gypsum (4000 kg/ha) and diammonium phosphate (DAP) (224, 336, or 448 kg/ha) were applied alone or in combination to 1.5 x 15 m treatment plots in May 2007 at two commercial lowbush blueberry (Vaccinium angustifolium Ait.) fields (Addison and Township 32, Maine). Soil Ca and S concentrations were raised by gypsum at both fields, when compared to the untreated control and DAP treatment. The release of nutrients in response to gypsum differed between fields. Gypsum was more effective in raising leaf P concentrations at the field where control soil P levels were higher yet the leaf P levels were lower. At the responsive field (Addison), leaf N deficiency was corrected by gypsum alone and by gypsum plus DAP. Leaf N concentrations were higher when DAP and gypsum were combined, at all rates when compared to DAP alone. Leaf K concentrations were increased by gypsum at both fields. Stem growth and flower bud formation were improved by DAP alone and sometimes enhanced by a combination of DAP and gypsum. At the responsive field (Addison) berry yield was increased by DAP at 448 kg/ha, compared to the control; and a comparable yield was recorded from plots receiving a lower rate of DAP (336 kg/ha) when it was combined with gypsum.