Nutrient Assimilation in Southern Highbush Blueberry and Implications for the Field

Blueberries (Vaccinium spp.) are adapted to a narrow range of soils that have low pH, high organic matter, and nitrogen in the ammonium form. Under more typical agricultural soil conditions of higher pH, lower organic matter, and nitrogen in the nitrate form, blueberry growth is sub-optimal. This is likely due, in part, to a limitation in the uptake and assimilation of nitrate-N. Studies indicate that nitrate uptake and assimilation are limited in highbush blueberry compared with ammonium uptake/assimilation. Increased dry weight accumulation under ammonium vs nitrate-N fertilization supports this.  Iron uptake and assimilation also appear to be reduced under high soil pH conditions, also contributing to decreased growth of blueberry in these soils.  V. arboreum (sparkleberry) is a wild tree-like species that is native to the southeastern U.S. and is found on low organic matter, higher pH (~ 6.0-6.5) soils. Sparkleberry is better able to assimilate nitrate-N and iron, especially under higher pH conditions, compared with highbush blueberry. These characteristics of sparkleberry may be exploited by using it as a rootstock for southern highbush blueberry (SHB). We currently have two plantings of grafted vs own-rooted SHB growing on amended vs non-amended soils with or without pH control. Canopy growth of grafted plants initially lagged behind that of own-rooted plants, but by the end of the second growing season (2013), canopy growth rate of grafted plants increased such that canopy volumes of grafted plants were similar to or greater than own-rooted plants, especially on non-amended, higher pH plots. In general, N, P, K, and Fe leaf concentrations were higher in SHB grafted onto sparkleberry rootstocks compared with own-rooted SHB, while leaf Ca and B were lower. Grafted plants generally had higher leaf chlorophyll concentrations throughout the season compared with own-rooted plants. Yields of grafted plants the first fruiting season (2013) were lower compared with own-rooted plants on amended soil, but similar to yields of own-rooted plants on non-amended soil. Since yields are highly correlated with canopy volume, we predict there will be very little yield difference between grafted and own-rooted plants in the second fruiting season, even on amended soils. Preliminary results suggest that limitations in nitrogen and iron uptake/assimilation may limit blueberry growth in non-amended, high pH soils; however, more research is needed in order to determine the ability of grafted blueberry to overcome nutrient deficiencies and maintain growth under these soil conditions.