Effects of mineral/organic fertilisation on the soil organic nitrogen pool in a semi-arid steppe

Compared to solely mineral fertiliser application, organic fertiliser substitution has been demonstrated to be effective in enhancing nitrogen cycling in cropland, but the relevant research based on grassland is still insufficient. A field experiment was carried out in the grasslands of northern China to examine the impact of mineral/ organic fertilisation on soil organic nitrogen fractions, activities of soil N-hydrolysing enzymes and their interrelationships. The results showed that the active soil organic nitrogen pool (hydrolysable NH4+-N + amino sugar-N + amino acid N) increased significantly after fertilisation, and organic fertiliser combined with mineral fertiliser addition showed the best promotion effect. N-acetyl-P-D-glucosaminidase, protease and urease activities are also significantly affected by fertilisation. The findings of our study indicate that the combination of mineral fertiliser and organic fertiliser shows a higher potential in improving the active soil organic nitrogen supply. This approach seems to be a viable agronomic strategy for augmenting soil nitrogen supply and ensuring the stability of the soil nitrogen pool in the semi-arid steppe region of northern China.