Influence of organic and inorganic nitrogen sources on soil microbial activity in tea gardens

Abstract:

Here is a paradox: tea demands heavy nitrogen—up to 300 kg ha^-1 year^-1—yet the cheapest N source, urea, may slowly degrade the microbial community that keeps the soil alive. This research compared five nitrogen management regimes (urea, farmyard manure, vermicompost, 50:50 FYM + urea, and an unfertilised control) on soil microbial biomass carbon (MBC), dehydrogenase, urease, and acid phosphatase activity in a 12-year-old tea garden at Valladolid, Spain, over two years (2021–2023). Vermicompost produced the highest MBC (467 µg g^-1), 64% above urea and 136% above the control. Dehydrogenase and phosphatase activity followed the same ranking. Urea-only plots showed the lowest enzyme activity among fertilised treatments, likely because repeated ammonium inputs lowered pH by 0.4 units. The 50:50 blend captured about 80% of the vermicompost advantage at lower cost. These results argue for partially replacing mineral N with organic sources to sustain the biological health of tea-garden soils.