Soil Profile Heterogeneity Strongly Affects Productivity in Young Almond Scion–Rootstock Combinations Grown in Unfertilized Mediterranean Soil

Spatial variability within soil profiles can substantially influence plant growth and productivity by modifying soil water and nutrient availability. In this study, we evaluated the relationship between soil physicochemical properties and productivity in a young almond orchard established on a Calcaric Solimovic Regosol under Mediterranean conditions. The soil profile comprised three horizons showing marked variability in depth and texture. Based on these differences, the experimental plot was divided into two zones: Zone A, characterized by a thicker upper horizon and a lower proportion of sand in the subsoil, and Zone B, with a thinner topsoil and higher sand content in the buried horizon. Within each zone, the almond cultivars ‘Marta’ and ‘Marinada’ were planted in a balanced design using two rootstocks: INRA GF-677 and GARNEM®. Almond productivity was the parameter most strongly affected by soil heterogeneity, showing pronounced differences among soil zones and rootstock–cultivar combinations. Almond productivity followed the sequence Marta > Marinada/GF-677 > Marinada/GARNEM®, and was reduced in Zone B by 37%, 68%, and 72%, respectively, compared with Zone A. In contrast, soil zones had no significant effect on leaf and kernel mineral nutrient concentrations, which varied mainly according to cultivar.