Quantitative analysis of straw returning on annual soil N₂O emission in the wheat–maize rotation system

ObjectivesNitrous oxide (N₂O) is one of the important greenhouse gases that mainly come from farmland soils. Straw returning is an effective ecological management in North China. Quantitative analysis of the N₂O emission and the affecting factors is of great significance for deep understanding of nitrification and denitrification mechanism in the wheat-maize system.

MethodsA field experiment with five different amounts of straw incorporation was carried out in the winter wheat and summer maize, including without straw returning (T0), returning 1875 kg/hm² wheat straw and 2000 kg/hm² maize straw (T1), returning 3750 kg/hm² wheat straw and 4000 kg/hm² maize straw (T2), returning 5625 kg/hm² wheat straw and 6000 kg/hm² maize straw (T3), and returning 7500 kg/hm² wheat straw and 8000 kg/hm² maize straw (T4). From October 2014 to October 2015, the N₂O flux was determined using static chamber technology combined with gas chromatography, the annual variation of N₂O flux and their relationships with soil temperature and moisture were analyzed.

ResultsThe straw returning amounts affected the N₂O flux significantly, which was increased with the increase of straw returning amounts. The seasonal N₂O emission was increased by 1.33–3.50 kg/hm² in amount, or 32.3%–85.1% in rates. The average N₂O flux were increased by 15.52–40.87 μg/(m²·h) in amount, or 32.3%–85.1% in rates. The average N₂O flux and total emission during the maize season were respectively 2.42–2.62 times and 1.05–1.14 times of those in the wheat season. The straw returning increased the temperature in 0–10 cm layer of soil by 0.63–2.14℃ and moisture in 0–20 cm layer of soil by 0.6%–1.8%, respectively. The correlation analysis showed that the N₂O flux had no correlation with soil temperature, had an exponential correlation with soil moisture in treatment T0, T1 and T2 (P < 0.05), but not with those in treatment T3 or T4.

ConclusionsWith the increase of straw returning amounts, the average N₂O flux and seasonal emission will be increased, which are higher in the maize season than in the wheat season. The straw returning could increase soil temperature in 0–10 cm layer and soil moisture in 0–20 cm layer significantly. The N₂O flux has an exponential correlation with soil moisture when the annual straw returning amounts are less than 7500 kg/hm², while had no correlation with soil temperature.