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Role of soil quality in declining rooibos (Aspalathus linearis) tea yields in the Clanwiliam area, South Africa
The global demand for rooibos tea is increasing whereas yields in the primary production area of Clanwilliam, South Africa are decreasing. Commercial rooibos producers report that tea yields decline over time since the initial clearing of the natural fynbos veld. Therefore, the aim of this study was to investigate soil and plant quality in cultivated rooibos plantations of various ages (1-60 y) and adjacent, wild rooibos stands in pristine fynbos in the Clanwilliam area. Soil chemical and physical properties, plant total biomass, tea yields, foliar elemental contents, extent of root N nodulation and mycorrhizal colonization were assessed. The most prominent soil quality changes observed at the oldest cultivated sites compared to pristine fynbos soils were: an increase in soil P, a general decline in total C and exchangeable basic cations, and a concomitant increase in exchangeable Al. Foliar N:P ratios notably declined at the cultivated sites compared to pristine fynbos sites indicating foliar P accumulation and lack of N. Soil P was strongly negatively correlated with rooibos root mycorrhizal colonization. The decline in soil organic matter and basic cations, especially K, was most strongly correlated with the decline in rooibos shoot biomass yields at cultivated sites. These findings highlight the significant role of soil quality in declining yields of rooibos tea in the Clanwilliam area. Management practices should be implemented that increase soil organic matter and essential basic cations such as K, and soil P and exchangeable Al levels should be monitored.
SR17029 Accepted 03 October 2017
© CSIRO 2017