Effects of combined organic and inorganic fertilizers on N₂O emissions in intensified vegetable field

Objectives Effects of combined application of organic manure (M) and inorganic nitrogen fertilizers (N) on annual N₂O emissions from vegetable fields were studied using the static chamber-gas chromatograph method.

Methods Field experiments were established in triplicates with four treatments:CK (without N application), NPK, M1N1 (M and N in the ratio of 1:1) and M2N1 (M and N in the ratio of 2:1), and N amount was equally applied in the N-fertilized treatments. Coriander herb, water spinach, baby bok choy and spinach were cultivated in turn with short time of fallow in between. The N₂O emissions were normally monitored in week frequency, but in every two days after fertilization and irrigation. Once N basal application was N 250 kg/hm² for crop except for water spinach with twice application. The total N input during the experiment was 1250 kg/hm².

Results N₂O emissions mainly emitted from April to October, which were significantly correlated with soil temperature in the 10 cm depth in all treatments. The N₂O flux in NPK treatment had significant correlation with soil inorganic nitrogen content, but in CK, M1N1 and M2N1 treatments, the N₂O fluxes had no significant correlations with soil nitrate, ammonium and inorganic nitrogen contents. In addition, WFPS (water filled pore space) ranged from 39% to 59% and no significant correlations between soil moisture and N₂O fluxes were detected during the experimental period. Compared with NPK treatment, the vegetable yields of water spinach had been significantly improved in M1N1 and M2N1 treatments, but there were no significant differences in cumulative vegetable yields between M1N1, M2N1 and NPK treatments. Compared with the NPK treatment, the cumulative N₂O emission and N₂O emission factor (EF) in the M1N1 treatment was significantly decreased by 36% and 64%, respectively. Meanwhile, compared with M2N1 treatment, the cumulative N₂O emission and N₂O emission factor (EF) in the M1N1 treatment was significantly decreased by 29% and 56%, respectively. But the effect in reducing N₂O emission was insignificantly in M2N1 treatment, compared with NPK treatment.

Conclusions Appropriate ratio of chemical and organic fertilizer is necessary for mitigating N₂O emissions in intensified vegetable fields. In the experimental conditions, the ratio of chemical N to organic N in 1:1 is satisfactory for ensuring vegetable yield and keeping low annual emission of N₂O.