Date of Award

2011

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Horticulture

Advisor

John M. Smagula

Second Committee Member

David Bryan Dail

Third Committee Member

Willaim Halteman

Abstract

Fertilizer application is one of the most important management practices in lowbush blueberry production. Improved plant nutrition was shown to improve blueberry production. The scope of this blueberry nutrition research encompasses the following three areas: 1) determining the most suitable rate of gypsum application for Maine lowbush blueberry soils, evaluating the effectiveness of a split application of gypsum, and identifying the soil characteristics that elicit a positive response to gypsum application; 2) evaluating the response of single node lowbush blueberry explants in vitro to different ratios of NH4- and NO3- nitrogen sources and 3) the analysis of multi-year leaf nutrient level-yield data from previous nutrient studies to confirm or to correct the nutrient standards currently being used. The use and application rate of diammonium phosphate (DAP) or monoammonium phosphate (MAP) had been recommended by the University of Maine researchers in the past decade. The increasing cost of DAP fertilization, coupled with the concern for environmental pollution due to inorganic fertilizer use, and increasing demand for organically grown lowbush blueberries led to the exploration of suitable alternative fertilizer for lowbush blueberry production. Gypsum was tested in Canada and a rate of 4000 kg*ha-1 was found to be effective in improving plant nutrition of lowbush blueberries but only increased blueberry yield at 50% of fields where it was applied. In a gypsum rate study, a 3363 kg'ha-1 rate of gypsum was found to be effective in raising leaf N and P concentrations up to the standards (N= 1.6%, P= 0.125%). A split application study showed that a split application of gypsum (2242 kg'ha-1 X 2) was not more effective than the single application (4484 kg'ha-1). In a study designed to identify soil characteristics that elicit a positive response to gypsum application revealed that a benefit to application of gypsum can be achieved in blueberry fields with high clay content and plants which were initially deficient in leaf N. In all three gypsum studies, lowbush blueberry yield was not improved by application of gypsum, compared to the control. Lowbush blueberry plants grow best in acidic soil and prefer the ammonium (NH4+) form of nitrogen (N). However, under tissue culture conditions, it was shown that blueberry plants grow in culture medium with NO3" as the predominant form of N. This discrepancy regarding the N preference of lowbush blueberry was tested by culturing single-node explants on tissue culture media having various NO3" to NH4+ ratios. It was found that the effect of the culture medium NO3" and NH4+ ratios on explant growth and development in this study was on shoot multiplication. A difference in NO3" to NH4+ ratio preference was also seen between the two lowbush blueberry clones used. Neither clone tolerated NO3" as the sole source of N. Leaf tissue analysis is recommended to help Maine lowbush blueberry growers make fertility management decisions. A set of leaf nutrient standards, called a second approximation, is currently being used to make fertilizer recommendations in Maine. The procedure which was used to establish these standards, however, was not clear. Recent studies have shown that some nutrient standards are not correct. Data collected from nutritional studies conducted by the University of Maine between 1991 and 2009 were used in two mathematical models, the boundary line approach (BLA) and quantile regression (QR) to calculate optimum leaf concentrations. Both procedures were effective in generating regression models from which optimum, minimum, and maximum leaf nutrient concentrations were derived. However, the soundness of BLA was questionable due to some arbitrary steps in the procedure. The nutrient concentrations calculated by the QR should be considered for future recommendations.

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