Spatial heterogeneous granulation enhance soil nitrogen supply potential via regulating dissolved organic nitrogen.

Combined application of organic fertilizer (OF) and chemical nitrogen (N) fertilizer (CF) is a common fertilization practice, providing better N supply pattern for crop growth. However, few studies focused on the effect of granulation method of these two fertilizers on N supply to soil. To validate this effect, we mixed the CF (N-(NH)SO) into cow manure powders with maize straw powder at rate of 2% or 8% (dry weight), respectively, in two forms, homogeneous granulation (HG) and spatial heterogeneous granulation (SG), and applied them to soil to investigate their difference in N transformations during an 80-day incubation. Results showed that there were more NH, NO and microbial biomass N (MBN) in the SG granules and the surrounding soil, while more dissolved organic N (DON) in the HG granules and the corresponding soil after day 30. At day 80, compared to HG, SG released less CF-N into the surrounding soil, but primed more organic N into mineral N. Structural equation model (SEM) revealed that DON was the main form of N transported from fertilizer granules to the surrounding soil, and then drove the changes of soil microbial activity, which determined the amount and dynamic of mineral N in the surrounding soil. These results indicated that, in heterogeneous granulation, the spatial separation between OF and CF slow down, but more importantly enhanced up, the microbial transformation of CF in the granules. This demonstrated that the spatial heterogeneous granulation of OF and CF could change the pattern of N release from fertilizer to soil and offer a potential way to optimize N fertilizer management strategies in the future.