Dynamics of maize straw–derived nitrogen in soil aggregates as affected by fertilization

The addition of maize residue nitrogen (N) to the soil strongly influences soil N accumulations, but the specific contributions of maize residue N to soil aggregates based on long-term fertilization remain largely unknown. This study involved a 360-day laboratory incubation experiment to determine the dynamics of N derived from maize straw in Mollisol soil aggregates applying different long-term fertilization treatments. In 2015, three soil samples from different fertilizers treatments were collected from the upper layer of soil (0–20 cm) of the field at a long-term Mollisol (Luvic Phaeozem) experimental site established in 1980 in Gongzhuling, Jilin Province, China. The fertilizer treatments included no fertilizer (CK); a combination of nitrogen, phosphorous and potassium fertilizers (NPK); and NPK combined with manure (MNPK). Three treatments of soils were incubated for 360 days at 25 °C, with or without 15N-labeled maize straw and destructively collected on days 45, 90, 135, 180 and 360. Soil samplings were separated into two aggregate fractions (macroaggregates, ≥ 0.25 mm; microaggregates, NPK > CK after 360 days of incubation. The results revealed that the combined application of chemical fertilizer and organic manure had higher capacity to retain maize straw–derived N, and more of it was retained in macroaggregates in the beginning. The addition of straw residue accelerated the formation of macroaggregates in the soils with lower C/N ratios.