Evaluation of different soil wetted surfaces in a high-density ‘Midknight’ Valencia orange orchard in Spain – preliminary results

The physiological and agronomic responses of imposing different soil wetted surface conditions by increasing the number of drippers per tree were evaluated in 4-year-old ‘Midknight’ Valencia orange trees (Citrus sinensis (L.) Osb.) grafted on Citrus macrophylla Wester in a commercial citrus orchard located in Pedralba (Valencia, eastern Spain). The tree spacing was 5×2 m, equivalent to 1,000 trees ha^‑1. The irrigation treatments consisted of two different agronomic designs of the irrigation system, but applying weekly the same amount of water: conventional design (CD) with two drip-lines (each one with integrated drippers of 1.75 L h^‑1 and spaced 0.50 m), one on each side of the tree, with 8 drippers tree^-1 and a design with a higher soil wetted surface (HSWS), in which the conventional design was implemented with an extra drip-line installed next to the trunk, supposing a total of 12 drippers tree^‑1. The first results have shown that differences in soil water distribution in HSWS trees did not alter plant water status during the low evaporative demand months. However, during high evaporative demand months (summer), the increase of soil wetted surface permitted to maintain better plant water status in HSWS trees, which was reflected in a higher leaf transpiration and stomatal aperture than in CD trees. The use of an extra drip line did not improve the yield parameters in the first season. With respect to the fruit quality, differences in soil water distribution did not produce changes in physical fruit parameters but slightly decreased the total soluble solids, without altering the maturity index. According to the preliminary results, the implementation of the irrigation system with an extra drip-line represents a promising alternative for enhancing irrigation water use in high density young citrus groves.