CaO/MgO nanoparticle-modified diatomite for co-retention of carbon, nitrogen, and phosphorus and mitigation of nutrient leaching from soil

Excessive accumulation of dissolved organic carbon (DOC), dissolved nitrogen (DN), and dissolved phosphorus (DP) in citrus orchard soils may increase the risk of agricultural non-point source pollution. The simultaneous and efficient retention of these dissolved nutrients in complex multi-solute systems, such as lemon waste fermentation broth (LWFB), remains a significant challenge, and the retention behavior of modified materials under such conditions is still poorly understood. Herein, a modified diatomite composite incorporating in situ loaded CaO/MgO nanoparticles (CMNPs@AD) was successfully synthesized via a facile acid-base activation strategy combined with an equal-volume impregnation method to investigate its nutrient retention performance and underlying mechanisms in LWFB. The results showed that CMNPs@AD featured a mesoporous structure decorated with uniformly dispersed metal nanoparticles. In the Langmuir isotherm model, the theoretical maximum retention capacities of CMNPs@AD for DOC, DN, and DP were 22.39, 45.02, and 25.49 mg/g, respectively. Advanced characterization techniques and density functional theory revealed that the nutrient retention mechanism of CMNPs@AD involves multiple physicochemical processes. Soil column leaching experiments showed that, compared with the fertilization group, the application of 1.0 wt% CMNPs@AD significantly reduced DOC, DN, and DP leaching while increasing soil sucrase, urease, and neutral phosphatase activities. The nutrient-laden CMNPs@AD (CMNPs@AD-CNP) significantly improved seed germination performance. Moreover, pot experiments demonstrated that plants grown in the post-leaching T2 soil showed enhanced growth and biomass accumulation and higher chlorophyll content than those in the other treatments. This study developed a novel and cost-effective soil additive that effectively reduced the co-leaching losses of dissolved soil nutrients, providing a promising material-based strategy for mitigating nutrient leaching from soil.