Effect of nitrogen fertigation management on soil nitrogen fractions and N₂O emissions from ratoon sugarcane fields

Objective  To study the effects of drip irrigation nitrogen (N) chasing management on soil N fraction and N₂O emission in host cane fields, and reveal the soil factors affecting soil N₂O fluxes.

Method  Two water drip irrigation levels of W0.8 (70%−80% of field water holding capacity) and W0.9 (80%−90% of field water holding capacity) and three drip irrigation N chasing ratios (250 kg·hm⁻² of equal N) were carried out in a mobile rain-proof shelter with the second generation host cane (Saccharum officinarum) as the research object. N0 was all the N fertilizer applied to the soil (referred to as soil-applied N); N5 was 50% soil-applied N and 50% applied by drip irrigation system (referred to as drip-applied N); N7 was 30% soil-applied N and 70% drip-applied N in the field trials. Soil N₂O flux, pH and nitrogen fraction content were measured at each period of sugarcane growth, and the relationship between soil N₂O flux and soil pH/nitrogen fraction content was analyzed.

Result  Soil N₂O flux was higher after two days of applying N fertilizer and water irrigation, and the soil N₂O flux of W0.9N5 was significantly lower than other treatments at the late tillering stage and maturity stage. Under W0.9, the cumulative soil N₂O emissions in N5 at the late tillering stage were 47.3% and 11.8% lower than those of N0 and N7, and 21.5% lower than those of N7 at the late elongation stage. Soil nitrate N content showed W0.9 > W0.8 for the same drip irrigation N rate, and increased with the increase of water irrigation. At the early elongation and maturity stage, the soil ammonium N content of N5 under W0.8 was 56.4% and 71.8% higher than those of N0, was 68.5% and 160.3% higher than those of N7. At the late tillering stage, soil microbial biomass nitrogen showed N5 > N7 > N0 under the same water drip irrigation level, and soil microbial biomass nitrogen of N5 was 120.0% and 100% higher than N0 under both water irrigation rates, respectively. There was a positive correlation between soil N ₂O flux and ammonium N content (r=0.313) and a negative correlation with nitrate N (r=−0.391).

Conclusion  W0.9N5 treatment can reduce soil N₂O emissions, and soil ammonium N content and nitrate N content affect soil N₂O flux, i.e., higher soil ammonium N content is associated with higher soil N₂O flux, while higher soil nitrate N content is associated with lower soil N₂O flux.