Effects of balanced and unbalanced fertilisation on tea quality, yield, and soil bacterial community

Unbalanced fertilisation with nitrogen (N), phosphorus (P), or potassium (K) deficiencies suppresses tea growth and is common in tea production. Balanced fertilisation based on the optimal nutrient requirements of tea plants improves tea yield and quality. However, the effects of unbalanced fertilisation on the yield and quality of tea, soil chemical properties, and bacterial community have not been investigated, and the mechanisms affecting the tea yield and quality remain unclear. Therefore, we conducted a five-year field experiment in tea orchards using four combinations of N, P, and K fertiliser and an unfertilised control. Compared with balanced fertilisation, N, P, and K deficiencies led to a 27.3%, 12.9%, and 11.3% reduction in annual tea yield, respectively. In general, N deficiency had a greater impact on the tea quality than P and K deficiencies. Nutrient contents in tea leaves correlated positively and significantly with tea quality (free amino acid and polyphenol contents). Alpha diversity of soil bacteria was lower in N addition treatments. The addition of N altered the soil bacterial community structure significantly and resulted in a lower Bray–Curtis dissimilarity with respect to the unfertilised treatment. Compared to balanced fertilisation, N deficiency inhibited Chloroflexi but favoured Thaumarchaeota growth. P deficiency resulted in a lower relative abundance of Acidobacteria but a higher relative abundance of Proteobacteria. Fertilisation indirectly influenced soil bacteria with the mediation of pH and soil organic carbon and NH4+ contents. This study indicates that N fertiliser input and pH are the main factors affecting tea yield and quality, respectively. Understanding the effects of unbalanced fertilisation on both tea and soil will help to guide fertilisation strategies, improve tea yield and quality, and reduce the environmental impacts of cultivation.