【Objective】 The study was carried out to investigate factors affecting the decomposition and nutrient release of wheat and maize residue under indoor and field conditions, so as to provide a theoretical basis for the rational return of crop residue and its suitable nutrient management practices. 【Method】 We conducted indoor incubation experiment with nylon bag and field experiment to study residue decomposition characteristics of wheat and maize under various nitrogen (N) fertilizer dosages (0, CK; 180 kg N·hm -1, N180; 360 kg N·hm -2, N360). In indoor environment, we focused on the effects of N dosage and soil types (Shajiang black soil: ST, Fluvo-aquic soil: FT), while in field condition, we emphasized on the effects of N dosages and burying depth (surface and 20 cm depth treatment) of the residue. 【Result】 Laboratory studies found that both residue types and soil types significantly affected residue decay constant, C, N, and P release. With the increasing of N application rate, the decay constant of wheat residue increased in both soil types, while the maize residue decreased. The N releases of maize and wheat residue decreased (the wheat residue increased in FT soil). The decay constant of wheat residue of the FT soil and the release of C, N, and P were significantly higher than those of the ST soil, while the soil types had little effect on the decomposition of maize residue. Under the lab incubation condition (180d), the average C releases of wheat residue were 370 g·kg -1, N was 4 g·kg -1, and P was 3.6 g·kg -1; maize residue C release was 560 g·kg -1, N was 11 g·kg -1, and P was 3.3 g·kg -1. Under field condition, the depth of residue returning significantly affected the decay constants of wheat and maize residue and the release of C, N and P. The decay constant and nutrient releases of residues treated with 20 cm were significantly higher than that of surface treatment. For surface treatment, the decay constant and C release of wheat residue declined gradually with the increase of N fertilizer application rate, but the maize residue increased. For 20 cm treatment, the decay constant of wheat residue and the release of C, N, and P increased with the amount of N fertilizer, while maize residue showed a decreasing trend. Under field condition, surface wheat residue biomass could decompose 40% after a maize growing season (June - October 2015), releasing 150 g C·kg -1, 2 g N·kg -1and 3.5 g P·kg -1; burying underground to 20 cm could decompose 80%, releasing 360 g C·kg -1, 4 g N·kg -1, and 3.8 g P·kg -1. Maize residues biomass could only decompose 40% after a wheat growth season (October 2015-June 2016) when the residues being returned to the surface, releasing 210 g C·kg -1, 5 g N·kg -1, and 2 g P·kg -1, but the 20 cm treatment could decompose 60%, releasing 360 g C·kg -1, 6 g N·kg -1, and 2.5 g P·kg -1. Principal component analysis showed that the decay constant of wheat residue under indoor conditions was significantly positively correlated with soil inorganic N, urease and straw N content, and negatively correlated with soil sucrase and straw C/N ratio, while maize residue decay constant was negatively correlated with soil inorganic N. Under field conditions, the decay constant of wheat residue was negatively correlated with soil urease, soil invertase, residue C content, N content and residue C/N ratio, while maize residue decay constant was negatively correlated with soil inorganic N content, soil urease, invertase and residue C/N ratio, and positively correlated with residue N and P content.【Conclusion】Both indoor and field experiment showed that the decay constants and nutrient release characteristics of wheat and maize residue were different. The application of N fertilizer promoted the decomposition of wheat residue but had little effect on the decomposition of maize residue. The soil types (ST and FT) significantly affected the decomposition of wheat residue, but the effects on maize residue decomposition were small. Returning crop residue to the soil could significantly promote the decomposition of wheat and maize residue and its nutrient release. In production, the crop residue should be returned to the soil, and appropriate N dosage should be adopted to soil types and residue types to promote the decomposition of straw.
