Photosynthesis, Yield, Nutrient Availability and Soil Properties after Biochar, Zeolites or Mycorrhizal Inoculum Application to a Mature Rainfed Olive Orchard
Soil conditioners and beneficial microorganisms are important tools that can be used to
increase the sustainability of agro-systems. However, the high diversity of conditions where they can
be applied may influence the results, which requires extensive field research. In this study, a field
trial of four years was conducted in olive (Olea europaea L.) to assess the effect of biochar, zeolites
and a commercial mycorrhizal inoculum in the photosynthetic performance, nutritional status of
trees, olive yield and soil properties. The experimental design also included a fertilizer treatment
with nitrogen (N), phosphorus (P), potassium (K) and boron (B), which nutrients were applied at
50 kg ha1 of N, P2O5 and K2O and 2 kg ha1 of B, and an untreated control. The mineral fertilizer
treatment increased significantly the dry mass of pruning wood and the average olive yield by 21%
over the control treatment. The mineral treatment increased plant N nutritional status, the most
likely reason why the trees of this treatment performed better. Overall, the soil treatments had net
photosynthetic rates similar to each other and higher than the control treatment, from the second
year onwards. Biochar increased soil organic matter, as a result of the carbon (C) contained in the
amendment itself, and probably by stimulating soil biological activity. Biochar and zeolites did not
improve the productive performances of the tress, but increased the soil cation exchange capacity
(CEC), which can benefit the system in the long-term. Mycorrhizal fungi did not show any benefit
for soil or plants, which could mean that mycorrhization was not established, or their effect was
not better than that of native microorganisms. In the conditions of this study, the interest of using
commercial mycorrhizal fungi in a mature olive orchard seems to be low.
This work was funded by the Operational Group “Novas práticas em olivais de sequeiro:
estratégias de mitigação e adaptação às alterações climáticas”, funded by PT2020 and EAFRD
(European Agricultural Fund for Rural Development). The authors are grateful to the Foundation for
Science and Technology (FCT, Portugal) and FEDER under Programme PT2020 for financial support
to CIMO (UIDB/00690/2020) and CITAB (UIDB/04033/2020) and also to AgriFood XXI project, nº.
NORTE-01-0145-FEDER-000041, co-financed by the European Regional Development Fund (ERDF)
through NORTE 2020 (North Regional Operational Program 2014/2020).
