No tillage and sugar beet foam amendment enhanced microbial activity of degraded acidic soils in South West Spain

• Long term experiment to assess soil quality recovery on acidic and degraded soils of SW Spain.
• No-tillage and Ca-amendment was the best combination to recover soil quality in acidic degraded soils.
• Microbial activity enhanced by sugar beet foam application to soil.

Ca-amendments are commonly applied to improve acid soils, whilst no-tillage (NT) has been widely recommended in soils where conventional tillage (CT) has led to losses of organic matter. However, the potential interactions between the two treatments are only partially known. Our study was conducted on a degraded soil located in SW Spain, in order to assess if the combination of Ca-amendment plus crop-tillage provides long term soil amelioration on microbial activity. To this end the effects of four different combinations of Ca-amendment and crop-tillage on selected key soil microbial properties were analyzed. The experimental design was a split-plot with four replicates. The main factor was the application or not of a Ca-amendment, sugar foam (SF) and control (C), and the second factor was crop-tillage, no tilled improved pasture (no tilled-IP) and conventional tillage forage crop (tilled-FC). Soil samples were collected from 2 soil depths after 7 years since the first SF application and after 1 year from a repeated SF application. The use of the Ca-amendment meant a higher pH although this effect was not found in the combination Ca-amendment plus no-tilled. Total organic carbon (TOC) was highly influenced by tillage, being higher for no tilled plots. The interaction found between tillage and amendment suggested that the beneficial effect of the Ca-amendment on organic carbon is lost after tillage practices. A positive effect on microbial biomass carbon (MBC) was found after a second SF application for the no tilled plots in the upper layer however the effect was opposite in the deepest layer where no differences in TOC were found. After a year from a repeated SF application, a clear positive effect of no-tilled was observed on β-glucosidase, β-glucosaminidase and urease activities at the superficial layer. This fact was not found in these enzymatic activities when the amendment application effect was studied but an interaction between tillage and amendment showed that the Ca-amendment plus no-tilled combination was the most favorable option to increase the activities of these enzymes. Values of dehydrogenase were higher in amended plots than in control for both soil depths regardless of the sampling date, showing a pH effect on its activity. From our findings, no tillage plus a Ca-amendment appears to be the most suitable choice for ensuring suitable production, through the accumulation of soil organic matter (SOM) and the improvement of biological properties.