Novel Diatomite/Hydroxyapatite/Biomass Ash Soil Conditioner Boosts Enzyme Activity for Sustainable Soil Management

A multi-component soil conditioner composed of wood biomass ash, diatomaceous earth, and calcium hydroxyapatite enriched with ammonium nitrate was evaluated for effects on soil enzymatic activity across soil depths during spring barley (Hordeum vulgare L.) cultivation and to identify a suitable application rate. A three-year pot experiment was conducted, using application rates of 10, 20, and 40 g per pot and compared with an unfertilized control. Soil samples were collected from depths of 0 - 5, 10 - 15, and 20 - 25 cm before sowing and after harvest. The activities of dehydrogenase, catalase, protease, urease, acid phosphatase, and alkaline phosphatase were determined using standard biochemical methods. Data were analyzed using analysis of variance and Pearson’s correlation analysis. The soil conditioner significantly increased enzyme activity, especially in the 0 - 5 cm soil layer. The lowest dose (10 g per pot) resulted in the strongest stimulation of dehydrogenase and urease activities, whereas catalase showed a stronger response at higher application rates; higher doses did not consistently increase biological activity in deeper soil layers. Acid phosphatase activity decreased with increasing dose, likely due to soil pH modification associated with the ash component. Low to moderate application rates were generally optimal for the biological activity of the tested soil conditioner. The NH₄NO₃-enriched calcium hydroxyapatite component additionally provided a source of nitrogen. These results indicate that the tested soil conditioner is a promising and sustainable soil amendment that enhances soil biological functioning while enabling the beneficial reuse of biomass ash in agricultural systems. Graphical Abstract