Potassium status in bulk and rhizospheric soils of olive groves in North Algeria

Olive (Olea europea L.) production is very important economically for many Mediterranean countries as in North Algeria where the present study took place. Traditionally, olive groves are found in nutrient poor marginal lands with no irrigation and on high slopes. Though K deficiency can negatively impact olive production, it is seldom corrected through fertilizer application due to farmers' lack of information on soil nutrient status and the prohibitive cost of K fertilizers. This study attempted to determine to what extent marginal lands (unsuitable for intensive cropping) in Northern Algeria planted with olive trees were K deficient and whether or not the soil K status impacted plant K status. To do so, bulk and rhizospheric soils as well as olive tree K foliar content were analyzed in 16 non-fertilized stations. The bulk soil of 7 of the 16 stations showed K deficiency. Different forms of potassium in the soils (water extractable, exchangeable and slowly-exchangeable forms) were observed to be systematically greater in the rhizosphere compared to the bulk soil. This increase was confirmed by the higher amount of “illite-like” clay layer minerals in the rhizospheric soils compared to those in the bulk soil. If rhizospheric soil properties were considered, only two stations remained K poor. Apart from the driest site, where K absorption was likely reduced due to extreme climatic conditions, these two stations were the only stations where foliar K content showed a K deficiency.This study showed that (i) the olive tree rhizosphere was systematically K enriched compared to bulk soils; (ii) that olive trees were especially suitable for growth on K poor soils and (iii) that marginal lands of North Algeria were on average less K poor than expected.

► Only 7 of the 16 studied soils of North Algeria planted with olive trees are K poor.
► K pools are systematically increased in the olive trees rhizosphere.
► This increase in K is confirmed by the higher amount of “illite-like” clay layers.
► Rhizosperic exchangeable K content and foliar K content are correlated.