Abstract: Fertilizer is usually difficult to apply in time at the jointing stage of wheat growth, due to the lack of labor force and weather constraints. Combined applications of organic and inorganic fertilizers have a longer nutrient supply period, but it is not clear whether they can alleviate low N stress in wheat at the jointing stage. In this study, we investigated the effects of the ratio of organic and inorganic fertilizer under delayed jointing fertilization on soil microbial community structure using real-time PCR, 16S rRNA, and ITS sequencing technology, and explored the relationship between microbial community structure and rhizosphere nitrogen mineralization, aiming to provide scientific basis for efficient cultivation of wheat. We conducted a positioning experiment with four treatments, i.e. only chemical fertilizer (T1), 15%, 30% and 45% sheep manure combined with chemical fertilizer (T2, T3 and T4). Soil samples were collected one day before the application of jointing fertilizer, which was delayed by 20 days. Nitrogen mineralization potential, bacterial and fungal abundance, diversity and community structure in rhizosphere soil were measured. The results showed that nitrogen mineralization potential of rhizosphere soil in treatments T2, T3 and T4 was 2.0, 1.7 and 2.2 times that of T1, respectively. There was no significant difference in bacterial abundance of rhizosphere soil among different treatments, while the abundance of fungi was decreased under various combined applications. Compared with T1, Chao1 index of bacteria was significantly increased by 5.1%, 7.0%, and 8.6% in the treatments of T2, T3, and T4, respectively. The Shannon index of fungi showed a decreasing trend as the proportion of organic fertilizers increased. Compared with treatment T2, the Shannon index of fungi under T4 was significantly decreased by 18.9%. Results of correlation analysis showed that nitrogen mineralization potential was positively correlated with bacterial Chao1 index and negatively correlated with fungal abundance. Results of redundancy analysis showed that soluble organic carbon content in rhizosphere soil was the main driving factor of bacterial community. Our results indicated that the combined application of organic and inorganic fertilizers under delayed wheat jointing fertilizer increased nitrogen mineralization potential of rhizosphere soil due to increased bacterial diversity of rhizosphere soil, thus enhancing soil nitrogen supply potential at wheat jointing stage under low nitrogen stress.

Key words: delayed jointing fertilizer, ratio of organic to inorganic fertilizer, nitrogen mineralization, fungi and bacteria.