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.