Can co-application of silicate rock powder and humic-like acids increase nutrient uptake and plant growth in weathered tropical soil?

Silicate rock powder (SRP) restores the fertility of weathered soils. However, its slow nutrient release is a disadvantage for short-duration crops. Humic-like acids (HLAs) are plant biostimulants that enhance root development and nutrient uptake. This work evaluates the effects of the co-application of HLA extracted from a vermicompost and SRP on the nutrient uptake and growth of maize cultivated in weathered soil in Brazil. The chemical composition of HLA was assessed using Fourier-transform infrared spectroscopy and 13Carbon-nuclear magnetic resonance, revealing an overall characteristic of hydrophobicity. A preliminary trial with different HLA concentrations (0, 20, 40, 80, and 160 mg L−1) revealed that 40 mg L−1 HLA resulted in the highest increase in the root area, dry root weight, H+ efflux, and the number of lateral roots, compared with other concentrations. The main experiment using soil treated with SRP at different rates (0, 600, 1200, 1800, and 2400 kg ha−1) showed that the co-application of SRP and HLA caused a significant difference in the root and total plant weights, compared with the sole SRP application. Furthermore, it increased the nutrient content of the plants. These effects are mainly because of increased proton pump activity and the hydrophobicity of HLA.