Natural, healthy soils usually harbor a variety of microorganisms that create a complex soil structure. They decompose biomass and thereby fix nitrogen and carbon. This creates humus while fine roots and the mycelium of soil fungi transport nutrients and build a stable soil structure. This prevents erosion and increases the ability to seep away and store water. All of these “ecosystem services” are offered to us by nature for free.

Aggressive management techniques destroy these complex structures. Both the physical structure and the binding capacity of nutrients and water are largely lost. Nutrient salts are being washed away, carbon is escaping into the atmosphere, erosion from wind and water is increasing… the soil is being depleted.

In the Sa Marina pilot project, we are also dealing with soil formation and regenerative cultivation in the “Permaculture fruit forest” system. On the former agricultural terraces, the spontaneous vegetation of shrubs and pines has been removed and most of the biomass has been triturated. The rainwater is channeled by key lines to seepage ditches filled with biomass. Next to them, a large number of trees, shrubs, grasses and herbs were planted. The variety of species used also serves to research the ability to adapt to climate change. The goal is a multi-level forest in which the different growth forms complement and enrich each other. Particularly fast-growing trees provide shade and are continually trimmed and used as mulch and green manure. A continuously covered earth surface protects against dehydration and UV radiation and offers the microorganisms the microclimate to decompose the biomass. When the carbon is broken down, symbiotic root bacteria bind atmospheric nitrogen and create complex structures (e.g. humus) that fix nutrients that are made available to the plants.

Over time, the healthy sponge structure of a natural soil with a rich biology develops again.

How well this soil improvement really works has now, 2.5 years after planting, been examined and compared with neighboring soils. The comparison areas are:
A:  Terraces that correspond to the original state before planting, i.e. impoverished, depleted soils from former agriculture, as well as
B:  Forest floor with dense vegetation with the usual sequence of spontaneous resettlement that took several decades to form the floor.

Samples were taken at depths of 10-25cm.

The results
The proportion of biomass in the soil has increased from 1.63% ( A ) to 3.89% and even exceeds the value of the forest soil (B, 3.41%). Most soils have between 1 and 2.5% MO, and only farms with strong conservation management (reduced tillage, high compost rates, soil conservation practices...) achieve levels above 3-4%!

The C/N ratio of 14.1 in the SAF indicates that management favors the accumulation of C, using a C/N = 10 as a reference value in cultivated soils. Reference value A: 10.53, B: 13.22. The increase in the carbon content in the soil is associated, among other things, with higher fungal activity and greater stability of the structure and aggregates.

The levels of total organic nitrogen and mineralized nitrogen are also reasonably high, indicating a good balance between organic N reserve (OM) and the biological activity of the mineralizing bacteria (35mg, A: 3mg, B: 8mg.)

Phosphorus (P) levels are equally low in all analyses, typical of soils on the Balearic Islands.

The pH value has dropped due to the activity of the soil organisms and thus the supply of macro and micronutrients has improved, especially potassium and magnesium.

Conclusion
The selected cultivation concept of fruit forest in permaculture and optimized use of rain has already fulfilled the great expectations in terms of carbon and nitrogen binding after 2.5 years. The soil structure has massively improved with a good ratio of macro and micropores and good structural stability. Rainwater can seep away much better and artificial irrigation is only necessary in extreme cases. Superficial runoff with erosion is now limited to heavy rain.

In the context of P-poor soils and an increasingly warmer climate, mycorrhization plays a fundamental role. In a natural forest, trees allocate up to 20% of carbohydrates to exchange with root mycorrhizal fungi, which, in addition to exchange and communication phenomena between plants, ensure better uptake of water, P and N.
The edible forest of Sa Marina offers optimal conditions for this, is a carbon sink and overall another excellent example of a nature-based solution as required by the IUCN and the EU Green Deal.