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Soil nutrient depletion threatens global food security and has been seriously underestimated for potassium (K) and several micronutrients. This is particularly the case for highly weathered soils in tropical countries, where classical soluble fertilizers are often not affordable or not accessible. One way to replenish macro- and micronutrients are ground silicate rock powders (SRPs). Rock forming silicate minerals contain most nutrients essential for higher plants, yet slow and inconsistent weathering rates have restricted their use in the past. Recent findings, however, challenge past agronomic objections which insufficiently addressed the factorial complexity of the weathering process. This review therefore first presents a framework with the most relevant factors for the weathering of SRPs through which several outcomes of prior studies can be explained. A subsequent analysis of 48 crop trials reveals the potential as alternative K source and multi-nutrient soil amendment for tropical soils, whereas the benefits for temperate soils are currently inconclusive. Beneficial results prevail for mafic and ultramafic rocks like basalts and rocks containing nepheline or glauconite. Several rock modifications are highly efficient in increasing the agronomic effectiveness of SRPs. Enhanced weathering of SRPs could additionally sequester substantial amounts of CO2 from the atmosphere and silicon (Si) supply can induce a broad spectrum of plant biotic and abiotic stress resistance. Recycling massive amounts of rock residues from domestic mining industries could furthermore resolve serious disposal challenges and improve fertilizer self-sufficiency. In conclusion, under the right circumstances, SRPs could not only advance low-cost and regional soil sustaining crop production but contribute to various sustainable development goals.
For several decades, farmers have been mixing rock powders with livestock slurry to reduce its NH3 emissions and increase its nutrient content. However, mixing rock powders with slurry is controversial, and there is currently no scientific evidence for its effects on NH3 and greenhouse gas (GHG) emissions or on changes in its nutrient content due to element release from rock powders. The major aim of this study was therefore to analyse the effects of mixing two commercially established rock powders with cattle slurry on NH3, CO2, N2O and CH4 emissions, and on nutrient release over a course of 46 days. We found that rock powders did not significantly affect CO2 emission rates. NH3 and N2O emission rates did not differ significantly up until the end of the trial, when the emission rates of the rock powder treatments significantly increased for NH3 and significantly decreased for N2O, respectively, which coincided with a reduction of the slurry crust. Cumulative NH3 emissions did not, however, differ significantly between treatments. Unexpected and significant increases in CH4 emission rates occurred for the rock powder treatments. Rock powders increased the macro- and micronutrient content of the slurry. The conflicting results are discussed and future research directions are proposed.
