Seasonal patterns in carbohydrates and macro nutrients in southern highbush blueberry plants

[摘要] ENGLISH ABSTRACT:Southern highbush (SHB) blueberries are relatively new to the blueberry industry and are adapted to grow in areas with low winter chilling and therefore can be grown in the Mediterranean-type climate of South Africa. The blueberry industry in South Africa is still relatively young, but it is quickly expanding and therefore appropriate cultivation practises are becoming more important. This study mainly focuses on the appropriate fertilization practises for SHB cultivars Snowchaser and Emerald grown in an ever-greening system.Plants were cultivated in plant containers in a netted tunnel in the Paarl district of South Africa. All plants received continuous fertigation with a standard commercial nutrient solution containing nitrogen, phosphorus, potassium, magnesium, calcium and all micro-elements. Carbohydrate patterns were determined on newly established tissue culture plants at two-weekly intervals from April 2013 to June 2014 and macro nutrient patterns were determined at four-weekly intervals from May 2013 to June 2014. The phenology of these plants was also visually assessed during the sampling period. Macro nutrient content was determined for two-year old „Snowchaser‟ and „Emerald‟ plants at five phenological stages during the 2013/2014 season and nutrient losses due to harvest and pruning was recorded.The phenology of evergreen „Snowchaser‟ and „Emerald‟ SHB blueberries were very different from deciduous blueberries, to such an extent that fruit could be harvested at the end of winter to early spring. Carbohydrate patterns differed between the first and the second season. Reserve carbohydrates were accumulated in the first season, but not in the second season possibly due to the difference in photosynthate production between the seasons. Plants were significantly bigger, with higher total leaf area, in the second season and it could be that carbohydrates from current photosynthesis were enough to supply new growth, thus making reserves less important. Carbohydrates could also have been used to increase flower bud development instead of being stored as reserves in the second season.Nutrient patterns also differed between the two seasons, but nutrient accumulation was apparent in the second season and not in the first. Nutrient uptake was highest when plants were growing rapidly, emphasizing the importance of fertilizer during periods of rapid growth. Huge fluctuations in the nutrient concentration patterns in the root, shoot and leaf tissues were observed over the sampling period and could have been a result of irregular fertigation and therefore it is uncertain whether flushes in nutrient uptake was a result of higher nutrient demand by the plant.Nutrients are lost due to harvest and pruning and need to be replaced by applying the right amount of fertilizer. Nutrient uptake differs throughout the season as the demand for nutrients fluctuates and therefore fertilizers should be applied at different rates during the season. In the two-year old plants, the most nutrients were accumulated after summer pruning and before growth cessation and therefore most of the fertilization would occur during this stage. Recommendations for correcting nutrient losses due to harvest and pruning are made, together with recommendations for rate and timing of fertilizer application throughout the season.

[发布机构] Stellenbosch University