Different soil particle size changes the ¹⁵N retention in soil and ¹⁵N utilization by maize

Improving soil structure is key to improving soil quality and nitrogen utilization efficiency (NUE) in global cropping systems. Soil sieving is a direct means of dividing soil activity into components with different practical functional significance. In order to have a more intuitive understanding of nutrient turnover and NUE under different soil particle sizes, we identified the key soil particle sizes that affect N cycling in cropping systems. An in-situ field experiment was conducted in Mollisol for three years using the ¹⁵N isotope tracer technique to examine the effect of soil structure on maize growth, nutrient uptake, and ¹⁵NUE. We artificially destructed the soil structure by sieving it into four particle size classes: (i) unsieved soil (CK), (ii) <0.5 mm size (A), (iii) 0.5-2 mm size (B), and (iv) 2-5 mm size (C). Then each year, the physical properties of the soil, ¹⁵N loss and retention rate (¹⁵NRR), the ¹⁵NUE, ¹⁵N absorption, and distribution, as well as maize growth and yield, were measured. The results showed that the 0.5-2 mm size (B) and 2-5 mm size (C) improved soil physical properties and increased the uptake of ¹⁵N by maize (especially in the leaves and grains), thereby increasing maize yield. The B and C particle sizes had lower soil ¹⁵NRR and higher alkaline hydrolysable N content than the other treatments in the depth. We concluded that the B sieving treatment is the key aggregate fraction to increasing maize ¹⁵NUE and yield and minimizing the negative effects on soil N retention capacity. Furthermore, the B treatment is key to affecting crop nutrient absorption and utilization.