A smart controlled-release fertilizer improved soil fertility but not olive tree physiology and yield

The use of a controlled-release fertilizer (CRF) was studied in a traditional rainfed olive grove in the northeast of Portugal where precipitation is very irregular, particularly in the spring. The objective of the study was to assess whether a CRF can improve the olive tree' s performance compared to a conventional nitrogen (N) fertilizer (CF), by supplying N gradually and reducing the risk of potential N loss from leaching. The fertilized treatments showed better plant N nutritional status, which resulted in enhanced net photosynthesis and higher leaf concentrations of total soluble sugars, chlorophylls and soluble proteins which, in turn, increased olive yield by 43% in comparison to the unfertilized control. Meanwhile, CRF show some advantages over the CF, although by an unexpected effect. Not in a direct way, by improving trees performance, but by enhancing soil fertility. The CRF treatments showed higher leveis of inorganic N in the soil by autumn, an aspect that at the outset could be interpreted as nega tive, since it could lead to N loss by leaching, but that proved to be a factor that may be behind the increase in the ol'ganic carbon, kjeldahl nitrogen and glomalin-related soil proteins. Thus, the availability of soil inürganlc-N in the autumn, in a climate in which excess precipitation and the risk of ieaching usually only occur in winter, led to weeds growth that seem to act as a catch crop, capturing residual inorganic N. Additionally, they contribute to protect the soil from erosion and to increase soi! organic matter, aspects that can benefit the agrosystem in the long-term.Ermelinda Silva acknowledge the financiai support provided by national funds through FCT (PD/BD/128274/2017), under PhD AgriChains (PD/00122/2012) and from the European Social Funds and the Regional Operational Programme Norte 2020. This study was also supported by CITAB research unit (UIDB/04033/2020). The research was integrated in the activities of 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). Ermelinda Silva also acknowledges the financiai support from NORTE 2020 throughout the ,CERES project (NORTE-OI-0145-FEDER-000082), funded by the Fundo Europeu de Desenvolvimento Regional (FEDER) and project NORTE-06-3559-FSE-000I03 funded by the Fundo Social Europeu (FSE), Livro