Physiological and growth responses of young plants of three native olive cultivars to olive waste compost

The recovery of olive mill waste compost as organic fertilizers, an integral part of the circular economy was investigated. Our study was focused on the evaluation of the morphological and agro-physiological responses of three olive oil varieties to the amendment with compost derived from the co-composting of various olive bio-wastes. An experiment was carried on one year old olive trees from three different olive oil varieties (Chemlali Zarzis, Chemlali Sfax and Chetoui). Plants were grown in pots filled by different mixtures compost/soil in various percentages (10%, 20%, 25% and 100%) in comparison with control plants grown in unamended sandy soil (0% compost). The effects of compost on morphological and agro-physiological plants parameters were studied regularly during the experimental period from March 2019 to October 2020. Our findings demonstrated that olive tree responses to fertilization were variable among varieties. A stimulation of olive trees growth was noted for plants in S10 (10% compost/90% soil) and S20 (20% compost/80% soil). Moreover, an improvement of leaf mineral content (Na+, K and P), photosynthetic pigments and plants fruits production was reported after compost amendment. However, compost does not modify olive leaf trait (leaf areas (LA), leaf dry matter content (LDMC) and leaf thickness (LT)). An inhibition of plants agro-physiological parameters was reported for S25 and raw compost (S100) for all tested varieties. Overall, the obtained results revealed that olive bio-wastes compost showed a fertilizing effect on young olive trees. The response of olive tree can be simultaneously influenced by compost quantities, olive varieties and also by the growth stage.