Effect of the addition of granitic powder to an acidic soil from Galicia (NW Spain) in comparison with lime

High amounts of granitic powders are produced in the granite industry in Galicia (NW Spain), whose accumulation could pose environmental threats, at least locally. Due to its natural alkalinity, the powder could be used to correct the acidity of soils or mining residues, where it would act at the same time as a source of plant nutrients. A greenhouse experiment was conducted to test the growth of Italian ryegrass on an acid soil amended with different rates of granitic powder (2.5, 5 and 10 %). Soil amended with lime or with lime in combination with P–K fertilizer, and the granitic powder alone, was used for comparison, with the unamended soil as control. After a growth period of 14 weeks, the plants were completely removed and washed; dry weight yield was recorded for roots and shoots, and their contents in nutrients and heavy metals were determined. Cation exchange capacity (CEC), pH, total C and N, nutrient elements and heavy metals were also determined in soil samples. The addition of granitic powder ameliorated the soil conditions for plant growth, with increments in soil pH, CEC and available nutrients, as well as a reduction of aluminium saturation. As a consequence, a significant increment in plant yield at increasing granitic powder rates was observed in comparison to the other amendments (up to 75 % higher than in the soil without amendment). The results of this study allow considering granitic powder as a suitable alternative to the traditional lime-based amendments for acid soils.