Spontaneous groundcover on olive grove management: effects on water infiltration and soil aggregate stability

Traditional olive grove management based on frequent tillage promotes erosion and soil structure loss. As a result, soil health decreases driving to degraded and impoverished soils. This problem is worst due to the location of olive groves in slope areas and the climate of central Spain, with long periods of drought and extreme rainfall events, which enhanced the erosion of bare soil. A shift to a more sustainable management model is needed, proposing groundcovers (GC) as an alternative to frequent tillage (TLL), aiming to increase soil organic carbon, protecting and retaining the soil from erosion and increasing nutrient cycling and, at the same time, enhancing other ecosystem services such as carbon sequestration and the increase in soil biodiversity. A trial was carried out in LEÑOSOST project (2018-2021) selecting 16 pairs of olive groves from different farmers in Madrid Region, with a low-density framework of approximately 70 trees·ha^-1 (12x12 m spacing). Each plot pair was composed of spontaneous groundcover management and its equivalent with traditional tillage. Soil sampling was carried out at four depths (0-5 cm, 5-10 cm, 10-20 cm and 20-30 cm) for the analysis of specific physical, chemical and microbiological soil properties, such as water-stable aggregates, calculated according to Kemper and Rosenau method (1986) and expressed as the percentage of micro-aggregates wet sieving resistant (< 2 mm diameter). Some soil physical properties were also measured "in situ", such as water infiltration, using a simple ring infiltrometer (Ø=12.5 cm) following the method described in USDA (2001). It has been observed that vegetation cover increases the infiltration rate almost twice in GC plots (109 mm·h^-1) than in TLL plots (52mm·h^-1), while the percentage of water-stable aggregates under 0-5 cm depth increased the most (49% under GC regarding 38% under TLL plots, p<0.05). Therefore, using groundcovers as olive grove management improves rainwater infiltration, enhancing water storage to be used by the olive tree, and allows the formation of soil aggregates that control soil erosion and host a large number of soil microorganisms thus, improving their functions of decomposition of organic matter and within the nutrient cycling, contributing to improve soil health.