Rehabilitation of a degraded acid Mediterranean soil after 11 years of by-product calcium amendments and pasture improvement

Resumen

The clearing of natural vegetation and tillage for agricultural purposes makes acid soils highly vulnerable to degradation, resulting in significant losses of soil fertility and crop productivity. This work focused on nature-based agricultural solutions to rehabilitate degraded acid soils in low-resource systems. We studied after 6 and 11 years how the introduction of a legume-rich pasture replacing a natural pasture or a tilled forage crop, with and without Ca-amendment, contributed to recover the soil health, the fertility and the productivity of degraded Ultisols in Western Spain. Industrial by-products, mainly sugar foam, were used as Ca-amendment to promote circular economy. The Ca-amendment factor influenced soil chemistry to 30 cm depth, while the type of soil use affected soil organic matter (SOM) to 15 cm; and both factors had positive effects on biomass productivity. Except for pH and Ca, no interaction between factors was found. Ca-amendment increased nutrient availability and soil pH, and Al ion precipitated at 0-15 cm depth. As a result, biomass production increased by 35% relative to no Ca-amendment. Forage cop produced 66% more biomass than pastures, but this increase did not translate into an increase in SOM. In fact, the legume-rich pasture was the best option to recover soil organic C and N levels, earlier and deeper. Over the 11 years, the use of pastures and Ca-amendment enhanced biomass production stability. Relative to natural, the improved pasture did not increase plant biomass but provided higher biomass stability and quality in terms of legume abundance, which was promoted when sugar foam was applied. Pastures also favoured key biological variable as earthworm's population, increasing it by four times with respect to forage crops. Compared to the non-amended and unfertilized natural pasture out of the experiment, the use of improved pasture, followed by natural pasture, combined with sugar foam and fertilization enhanced soil health, soil fertility and biomass production stability. Thus, this solution has proven effective for restoring degraded acid soils, promoting diversity and mitigating climate change, while offering a more economically beneficial alternative.