Gypsum Rate Evaluation for Wild Lowbush Blueberry (Vaccinium angustifolium Ait.) Soils

Four rates of gypsum (CaSO4 center dot 2H(2)O) were compared at two commercial wild lowbush blueberry fields (Addison and Belfast, ME) to determine the most suitable rate for increasing blueberry nutrient uptake under Maine soil conditions. Gypsum treatments (1,121, 2,242, 3,363, or 4,484 kg.ha(-1)) were compared to diammonium phosphate (DAP; 448 kg.ha(-1)) and a control. Gypsum and diammonium phosphate were applied pre-emergent in May 2009 to 0.9 m x 15 m plots arranged in a randomized complete block design with six blocks in each field. Composite leaf and soil samples were collected in July 2009 and analyzed for nutrient concentrations. Within each treatment plot, stems from four randomly placed 0.023 m(2) quadrats were collected in October 2009 for stem length, branching, and flower bud measurements. Soil Ca and S concentrations were increased by gypsum at both fields. Gypsum increased leaf N and P concentrations only at the field that was deficient in these nutrients (Addison). Diammonium phosphate increased leaf N and P concentrations compared to the controls at both fields. Gypsum at 2,242 kg.ha(-1) or higher corrected P deficiency; but only the 3,363 kg.ha(-1) and 4,484 kg.ha(-1) rates corrected leaf N deficiency. At Belfast, diammonium phosphate did not increase flower bud density or yield. At the deficient Addison field, a lower rate of gypsum (3,363 kg.ha(-1)) than that recommended for Canadian soils (4,000 kg/ha) was effective in correcting leaf N and P deficiency. Flower bud density and yield were raised by diammonium phosphate but not by any of the gypsum treatments.