Purpose To investigate the effects of reducing nitrogen fertilizer by 25% and applying different amounts of organic fertilizer and biochar-based organic fertilizer on the growth of flue-cured tobacco, soil chemical properties, and bacterial communities.
Methods Four treatments were set: 25% reduced nitrogen fertilizer combined with 1% organic fertilizer (OF-1), 25% reduced nitrogen fertilizer combined with 2% organic fertilizer (OF-2), 25% reduced nitrogen fertilizer combined with 1% biochar-based organic fertilizer (BCOF-1), and 25% reduced nitrogen fertilizer combined with 2% biochar-based organic fertilizer (BCOF-2), taking conventional fertilization as the control (CK). The study analyzed the effects of different organic material applications on tobacco plant growth, above-ground nutrient content, soil chemical properties, and soil bacterial community structure and diversity.
Results 1) The biomass of tobacco plants in the OF-1 treatment was significantly higher than that in CK, with an increase of 27.14%; the plant height in OF-1 and BCOF-1 treatments was significantly greater than that in BCOF-2, with increases of 32.95% and 34.95%, respectively; the total phosphorus and potassium contents in the above-ground parts of plants under OF-1 and BCOF-1 treatments were significantly higher than that in CK, while the total phosphorus content in the above-ground parts under OF-2 and BCOF-2 treatments was significantly lower than that in CK. 2) The soil organic matter content in OF-1, OF-2, BCOF-1, and BCOF-2 was significantly higher than that in CK, with increases of 149.06%, 307.86%, 100.76%, and 175.21%, respectively. The OF treatment significantly increased soil ammonium nitrogen content, whereas the BCOF treatments had no significant effect. 3) All OF-1, OF-2, BCOF-1, and BCOF-2 treatments increased the relative abundance of Firmicutes. The bacterial Chao1 richness index of the BCOF-1 treatment was significantly higher than that in OF-2. 4) Redundancy analysis indicated that soil organic matter, nitrate nitrogen, and ammonium nitrogen were the key factors influencing the bacterial community structure.
Conclusion Under the condition of reducing the application of 25% nitrogen fertilizer, the effectiveness of combining organic materials depends on their type and amount. Among them, combining 1% organic materials can effectively promote tobacco plant growth and nutrient absorption, while combining 2% organic materials may inhibit phosphorus and potassium absorption. Conventional organic fertilizer tends to increase the accumulation of available ammonium nitrogen, whereas biochar-based organic fertilizer, owing to its absorptivity, may contribute to build a “slow-release nitrogen pool”. The two materials regulate soil nutrients and reshape microbial communities through different mechanisms.
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