Subsurface drip irrigation affects trunk diameter fluctuations in lemon trees, in comparison with surface drip irrigation

The aim of this work was to assess the suitability of using trunk diameter fluctuations for irrigation scheduling in a subsurface drip irrigation system in adult lemon trees. The experiment was carried out over two consecutive years in an experimental orchard located in Torre Pacheco (Murcia, Spain) in 18-year-old ‘Fino 49’ lemon trees (Citrus limon (L.) Burm. fil.) grafted on Citrus macrophylla Wester. Well-watered trees were maintained with surface (SUR) and subsurface (SUB) drip irrigation systems by applying irrigation water independently, maintaining in both systems the soil water content of the root zone at ≈80% of the amount of water available and the midday stem water potential (Ψstem)>−1.3MPa. Following these criterias for irrigation scheduling, the use of the SUB system increased the water use efficiency in lemon trees, due to an irrigation water saving of 19% without the yield being affected. However, the SUB system induced different trunk growth dynamics, which produced different reference equations for the maximum daily trunk shrinkage (MDS) and Ψstem. In spite of this, the prediction power of MDS was similar for both systems. In both cases, the environmental variable that best correlated with Ψstem and MDS was the daily mean air temperature. Thus, based on these results, MDS measurements can be suitable for adjusting the irrigation scheduling of lemon trees, but differences found between irrigation systems in the MDS reference baselines highlight the necessity of determining the baselines for each irrigation system.