Impact of straw and rock-fragment mulches on soil moisture and early growth of holm oaks in a semiarid area

- Straw mulch favored water infiltration and water storage in soil depth.
- Rock-fragment cover increased the soil moisture only at 10-20 cm.
- Mulching increased the days of plant growth and diminished days of stress.
- Mulching with rocks can be more useful for plants with shorter initial root systems.

Planted seedlings and saplings usually exh\ibit low survival and growth rates under dry Mediterranean environments, especially late-successional species such as Quercus. In this work, we studied the effects of straw and rock-fragment mulches on the establishment conditions of holm oak (Quercus ilex L. subsp. ballota (Def.) Samp.) in SE Spain. Soil moisture was characterized at 4 soil depths (10, 20, 40, and 70 cm) for 3 treatments applied over 1 × 1 m plantation beds (rock-fragment cover [caliche], straw mulch, and control) where holm oak saplings were outplanted. Digital dendrometers were used to characterize sapling-growth characteristics including: physiological stress, cumulative growth, and number of days of growth. The results showed that straw mulch favored water infiltration and soil-water storage at 20, 40, and 70 cm in depth. By contrast, the rock fragments improved soil moisture only at 10 and 20 cm in depth with respect to the control, decreasing the water storage in deeper soil layers. Despite the absence of significant total growth differences after 20 months of tree monitoring, both types of mulch lengthened the number of days of plant growth and shortened the number of days of physiological stress in our holm oak saplings. The application of straw mulch or a rock-fragment cover changed the spatial and temporal soil-moisture distribution pattern throughout the soil profile. Straw mulch would be recommended for seedlings or saplings with deeper initial root systems (i.e. containers > 20 cm high), whereas caliche-type rock fragments could be more suitable for small seedlings with shallower initial root systems (i.e. containers < 20 cm high), or species with superficial root systems, such as Pinus species or other conifers.

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