Functional Biofertilizer with Microbial and Enzyme Complex Improves Nutrients, Microbial Characteristics, and Crop Yield in Albic Soil of Heilongjiang Province, China

Soils with an albic horizon (characterized by a bleached, nutrient-poor eluvial layer), classified primarily as Albic Planosols and associated groups (e.g., Albic Luvisols and Retisols) in the World Reference Base for Soil Resources (WRB), are widespread in Northeast China and suffer from inherent poor nutrient availability and low crop productivity. The present study aimed to evaluate the efficacy of novel microbial–enzyme composite biofertilizers in ameliorating Albic soils. This comprehensive assessment investigated their effects on soil nutrient availability, microbial community structure, and the activities of key enzymes involved in nutrient cycling (e.g., dehydrogenase and phosphatase). Concurrently, the impact on maize crop performance was determined by measuring changes in agronomic traits, including chlorophyll content, stem diameter, and final grain yield. A field experiment was conducted in Heilongjiang Province during the 2023 maize growing season using a randomized block design with six treatments: CF (conventional chemical fertilizer, 330 kg·ha−1 NPK), OF (chemical fertilizer + 1500 kg·ha−1 organic carrier), BF1 (OF + 75 kg·ha−1 marine actinomycetes), BF2 (OF + 75 kg·ha−1 actinomycetes + 45 kg·ha−1 phytase), BF3 (OF + 75 kg·ha−1 actinomycetes + 45 kg·ha−1 mycorrhizal fungi + 45 kg·ha−1 phytase), and BF4 (OF + 75 kg·ha−1 actinomycetes + 45 kg·ha−1 mycorrhizal fungi + 45 kg·ha−1 phytase + 45 kg·ha−1 β–glucosidase). The results showed that biofertilizers significantly increased microbial abundance and enzyme activity. The integrated treatment BF4 notably enhanced topsoil fungal abundance by 188.1% and dehydrogenase activity in the 0–20 cm layer, while also increasing available phosphorus by 92.6% at maturity. Although BF4 improved soil properties the most, BF3 produced the highest maize yield—boosting grain output by 18.3% over CF—and improved stem diameter and chlorophyll content. Strong correlations between microbial parameters and enzyme activities indicated a nutrient-cycling mechanism driven by microorganisms, with topsoil fungal abundance positively linked to alkaline phosphatase activity (r = 0.72) and subsoil bacterial abundance associated with available phosphorus (r = 0.65), demonstrating microbial–mediated carbon–phosphorus coupling. In conclusion, microbial–enzyme biofertilizers, particularly BF4, provide a sustainable strategy for enhancing Albic soil fertility and crop productivity.