Irrigation of Young Cork Oaks under Field Conditions—Testing the Best Water Volume

Constança Camilo-Alves,Margarida Vaz,Nuno Almeida Ribeiro,João M Barroso,Cati Dinis

doi:10.3390/f11010088

Abstract

This study is the beginning of the first long-term study on cork oak irrigation under field conditions, with a structural-functional approach. Cork oaks are currently facing disturbances affecting cork quality and quantity, jeopardizing the future of the economic sector. There is a need for new production techniques that maximize cork oak growth and vitality. In this study, irrigation was implemented in a new intensive cork oak plantations to test the best irrigation volume. The long-term goal is to improve tree growth with minimum water requirements. A 6 ha intensive plantation was installed in Coruche, Portugal. The experimental plot consisted of a subsurface drip fertigation system, buried 40 cm deep; with five independent irrigation treatments. It was tested four irrigation volumes during the dry period—21 weeks in the summer of 2016—ranging from 1.88 mm to 5.62 mm a week. Information on meteorological conditions, soil moisture profile and leaf stomatal conductance were gathered periodically and dendrometric measurements were performed before and after the treatments. Cork oaks’ structural and functional parameters were associated with irrigation volume Response to irrigation showed an inflection point in treatment 2, corresponding to a water supply of 3.12 mm per week: below the inflection point, stomatal conductance was reduced by 15% and relative diameter growth at the base was reduced by 10%. Stomatal conductance also showed a positive relationship with soil moisture below the irrigation tubes and with plants’ stem diameter. In conclusion, irrigation supply during the period of water stress improved function and structure of cork oaks seedlings under field conditions. These results suggest that irrigation can be a viable alternative to improve cork oak growth in afforestation and reforestation.

Highlights

Cork oak (Quercus suber L.) is a sclerophyllous evergreen Mediterranean tree of high conservation and socioeconomic value in its natural range area
These results strongly indicate that a summer subsurface drip irrigation campaign with a total of 655 m3 of water supplied 3 times a week is applicable to cork oak seedlings growing on deep sandy soils
A 3-fold increase in water corresponded to a 15% increase in stomatal conductance and a 10%

Summary

Introduction

Cork oak (Quercus suber L.) is a sclerophyllous evergreen Mediterranean tree of high conservation and socioeconomic value in its natural range area. This species covers about 2.2 M ha in the western part of the Mediterranean basin, growing well in acidic soils on granite, schist, or sandy substrates [1]. The main product obtained from this tree is its outer layer, cork. Portugal produces about half of the cork on the market (≈100,000 ton per year) and the remainder is mainly obtained in Spain, Morocco, Argelia, Tunisia, Italy and France [2]. Cork oak forests and the derived silvopastoral systems are ecologically and economically sustainable, serving as an important tool in preventing desertification [2].

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