Opportunities for better nutrient management in blueberry

Leaf tissue testing is commonly used in modern agricultural systems to portray plant nutrient profiles. However, for leaf analyses to be useful there needs to be an optimal or desired range for each nutrient. Whilst nutrient standards are available for blueberry and are updated occasionally, much of the data are based on older cultivars and is not necessarily applicable to all growing regions. Moreover, only rarely has there been a distinction made between nutrient profiles of cultivars derived from highbush (HB), Vaccinium corymbosum, and rabbiteye (RE), Vaccinium virgatum, species, including their hybrids. In this study, nutrient profiles for two blueberry cultivars: 'Sunset Blue' (HB) and 'Centra Blue' (RE) were measured and compared every two weeks between mid-spring and mid-summer. Significant differences were found between the two cultivars in levels of potassium (p=0.008), iron (p=0.016) and copper (p=0.039). This indicated that nutrient standards for blueberry cultivars grown in New Zealand may need to be updated and changed to better reflect cultivar differences. When comparing nutrient levels against the week number after the trial commenced, we found significant temporal changes in nutrient levels for nitrogen (p=0.01) and phosphorus (p=0.003). These data lend support to the need for both spring and summer optimum ranges. Chlorophyll meter measurements correlated well with magnesium (p=0.011) and iron (p=0.012), with iron determined as the most likely nutrient that could influence production. Nitrogen levels were within the optimum range for both cultivars, irrespective of growing regime, and had no effect on chlorophyll measurements.