Super high-density (SHD) olive orchards are rapidly expanding since the first plantation was set up in Spain in the 1990s. Because there are no long-term studies characterizing these systems, it is unknown if densities above a certain threshold could trigger competition among fully-grown trees, compromising their development. Over 14 years we have evaluated the performance of the major olive cultivars currently planted in SHD systems (‘Arbequina’, Arbequina IRTA-i·18R, ‘Arbosana’, ‘Fs-17’, and ‘Koroneiki’) and nine SHD designs ranging from 780 to 2254 trees ha-1 for the cultivar ‘Arbequina’. Remarkably, the accumulated fruit and oil production of the five cultivars increased linearly over time. Our data indicated the favorable long-term performance of the evaluated cultivars with an average annual oil production of 2.3 t ha-1. Only ‘Fs-17’ did not perform well to the SHD system in our conditions and it yielded about half (1.2 t ha-1) of the other cultivars. In the density trial for ‘Arbequina’, both fruit and oil accumulated production increased over time as a function of tree density. Thus, the accumulated oil yield ranged from 16.1 t ha-1 for the lowest density (780 trees ha-1) to 29.9 t ha-1 for the highest (2254 trees ha-1). In addition, we note that the accumulated production per surface unit showed a better correlation with the hedgerow length than the tree density. Thus, the current planting designs of SHD olive orchards can be further improved taking this parameter into account. Despite observations that some irregular patterns of crop distribution have arisen, our olive hedgerows are still fully productive after 14 years of planting. This result contradicts previous experiences that showed declines in production seven or eight years after planting due to high vigor, shading, and limited ventilation.

Applying pruning residues in the lanes of olive groves has become a popular practice because it is economical and accrues benefits for soil and water management. This study presents an analysis of the impact of different rates of pruning residue on soil properties, in particular related with soil quality. Over 4 annual campaigns, chopped pruning residues used as a mulch were analyzed in terms of composition, coverage and moisture content to evaluate their effects on the amount of soil organic carbon (-10 cm and -20 cm) and CO₂ emissions, temperature and moisture. The experiment was carried out in a super-intensive olive orchard in Cordoba (SE, Spain) and used four amounts of fresh pruning residue: 7.5 t ha^⁻1(T1), 15.0 t ha^⁻1 (T2) and 30.0 t ha^⁻1 (T3), with a control T0 = 0.0 t ha¹. Mulch mean leaf fraction was 46.0 ± 17.5% (±SD) and initial water content, 24.8 ± 8.6%. The mulching benefits for soil moisture were observed in amounts of pruning residue >7.5 t ha^⁻1, which are only produced in super-intensive olive groves or in orchards with high tree densities. The low impact of the treatments on soil moisture was explained by the dramatic annual variations in residue moisture contents, caused by the regimes of high temperatures and rainfall-evapotranspiration deficits inherent to the Mediterranean Basin climate. Thus, the mulching capacity only resulted efficient when the residues were still humid in spring. In addition, 15.0 t ha^⁻1 of pruning residues was the threshold to provide significant increases in soil organic carbon at depths of 0-20 cm. Thus, accumulating pruning residue in lanes at rates of over 15 t ha^⁻1 (T2 and T3) is more convenient than a uniform distribution with lower amounts, due to the low mineralization rates occurring during warm seasons and the larger inputs of OM increasing the annual balance of SOC.