Effects of untreated two-phase olive mill pomace on potted olive plantlets

Two-phase pomace represents an important environmental problem in Mediterranean areas. With its high organic content, direct application of two-phase pomace in the field is recommended to improve soil organic carbon levels and fertility. However, this does not consider any antagonistic effects that this application might have on root proliferation and biomass partitioning. We studied the effects of untreated two-phase pomace on properties of growth substrate, and on shoot and root growth and biomass allocation of potted olive plantlets. A pot experiment was carried out in a greenhouse over 90 days, with five levels of two-phase pomace and using two olive cultivars. The effects on shoot growth, leaf pigment content and maximum quantum efficiency of photosystem II (ΦPSII) were assessed each month. After 90 days, the shoot and root biomass of the olive plants was quantified, along with total organic matter, and carbon, nitrogen and polyphenol contents of the growth substrate and shoots, and the fine root nutritional status. Two-phase pomace increased the total organic matter, total nitrogen and polyphenol contents of the growth substrate. It significantly altered biomass partitioning in the olive plantlets, with reduced shoot dry mass and leaf area, and new shoot formation. It also increased fine and total root dry mass for all two-phase pomace levels except 40%. There were no significant differences in leaf pigment content and ΦPSII across the treatment levels. Therefore, application of untreated two-phase pomace at more than 4% induces a severe imbalance in olive plantlet biomass partitioning, and shoot and root growth.