Optimizing water resources in dry-land olive groves represents a crucial challenge for modern olive growing, especially in sandy soils. An experiment conducted by Celano et al. (2011) analyzed the impact of two different management systems on water dynamics in the soil: the system worked (continuous processes) andthe grassy system (permanent spontaneous grassing, mowed at least twice a year with the release of shredded pruning residues).
To map the moisture distribution in the soil profile, the research employed the geoelectrical technique, validated by the gravimetric method (sample weighing). This methodology allowed monitoring the soil's electrical resistivity, a parameter closely related to volumetric water content, up to a depth of 3 meters.
Water recharge dynamics compared
The study monitored three key phases, corresponding to the autumn-winter and pre-summer recharge periods.
November (initial phase): After the first autumn rains (58 mm), the grassed system already showed a higher water content, especially beyond 0,6 meters in depth. In contrast, the tilled system had low and uniform water levels along the entire profile.
January (climate anomaly): Despite an additional 61 mm of rainfall, the low rainfall combined with high temperatures caused water loss in the layers between 0,6 and 1,8 meters in the grassed system, due to transpiration of grass and olive trees. The treated system, however, showed slight accumulation limited to the surface layers (0-0,9 m).
April (full charge): Thanks to consistent rainfall (211 mm), both systems benefited from enrichment. However, the grassed system accumulated water in the deepest areas, essential for the olive tree roots, while the tilled system showed slow recharge and limited to the first 60 cm.
Why is grassing more efficient?
The superior water-absorbing properties of grassy soils lie in the soil's physical structure. Macroporosity is greater and more evenly distributed, thanks to the presence of "transmission pores" (50-500 μm) created by roots and earthworm activity.
Permeability: In grassy soil, water flows freely along the entire profile. In the tilled system, infiltration is hindered by the formation of surface crusts and a compact layer (tillage) that limits the vertical movement of the fluid.
Organic substance: The addition of plant residues and prunings improves water retention capacity and acts as a natural mulch, drastically reducing direct evaporation from the soil.
Water consumption analysis
Despite its greater storage capacity, the grassed system consumes more water. Between November and January, grassed consumption was almost double that of processed crops. This is due to the "double pump" of transpiration: that of the grasses and that of the olive trees, which in mild climates never completely shut down their metabolism.
In spring, consumption by the grassed system increased further (+32%), but the processed system also recorded a peak (+55%) due to the greater availability of surface water and the increase in environmental demand (ETo).
Conclusions: towards rational management
Geoelectric technology has confirmed that Grassing, if well managed, is a powerful tool for the conservation of deep water reserves, often overlooked, but vital during the summer droughtHowever, to prevent water competition between grass and olive trees from becoming harmful, management must be strategic:
Timeliness of mowing: the grass cover must be removed before the critical stages of the olive tree (flowering and fruit setting).
Mulching effect: The residues left on the surface protect the soil, although in high fire risk areas a light surface burial may be necessary.
In short, grassing transforms the soil into a more efficient "sponge," capable of exploiting even light rainfall to replenish the olive grove's deep reserves.
