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

PurposeThe 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.Materials and methodsIn 2015, three soil samples from different fertilizers treatments were collected from the upper layer of soil (0-20cm) 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 360days at 25 degrees C, with or without N-15-labeled maize straw and destructively collected on days 45, 90, 135, 180 and 360. Soil samplings were separated into two aggregate fractions (macroaggregates, 0.25mm; microaggregates, <0.25mm) using the wet sieving method.Results and discussionThe higher amounts of maize straw-derived N were incorporated into the macroaggregate on day 90 in the three treatments (average of 65.4%) and into the microaggregate in the MNPK (11.5%), NPK (9.5%), and CK (6.7%) treatments on days 360, 360, and 45, respectively. The maize straw-derived N remaining in the soil aggregates (macroaggregate and microaggregate) was in the order of NPKM>NPK>CK after 360days of incubation.ConclusionsThe 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.