Contribution of nitrogen sources to NH₃ volatilization in plastic-shed soilrevealed by ¹⁵N natural abundance

Objectives Excessive nitrogen (N) fertilization results in serious ammonia (NH₃) volatilization in plastic-shed vegetable production in China. The NH₃ volatilization as affected by fertilizer types was studied using the ¹⁵N natural abundance in the fertilizers, and the contribution rate was quantitatively analyzed for the scientific nitrogen management with less nitrogen loss.

Methods A 40-day tomato-pot production experiment was conducted, the test brown soil was neither applied with any fertilizer nor used for cropping. Taking no N fertilizer as control (CK), three treatments at the same N basal application rate (N 3 g/pot) were set up, i.e. only chicken manure compost (M), only urea fertilizer (U), and half chicken manure half urea (MU). The NH₃ volatilization rate and cumulative emission were monitored by static chamber method. The contribution of fertilizer to total NH₃ volatilization in soil was quantified by the ¹⁵N natural abundance method.

Results The NH₃ volatilization rate increased rapidly and reached peak within 3 to 6 days after basal N fertilization, and then slowly decreased to the level of pre-fertilization at the 33th day after the basal N fertilization. The net NH₃ volatilization accumulation in M treatment was 60.8% and 63.1% lower than in MU and U treatment, respectively (P<0.05), and that in MU (4.62%) was not reduced significantly, relative to U treatment. The corresponding NH₃ volatilization coefficients were 1.37% (U), 1.29% (MU) and 0.51% (M), respectively. The measured δ¹⁵N-NH₃ values decreased rapidly as the NH₃ volatilization proceeded, and gradually increased to the level of pre-fertilization. The M treatment had higher average δ¹⁵N-NH₃ values compared to the MU and U treatments. The contribution to NH₃ volatilization were 30.5% for chicken manure in M treatment, 53.1% for urea in U treatment, and 28.6% and 56.6% for chicken manure and urea in the MU treatment, respectively.

Conclusions Under the same fertilizer N rate, application of chicken manure could reduce the total NH₃ volatilization significantly, but the combined application of chicken manure and urea would not show significantly mitigation effect, compared to urea application. Isotope fractionation analysis during NH₃ volatilization revealed that the contribution of chicken manure and urea to soil NH₃ volatilization is not significantly affected by single or combined application. Therefore, controlling the chemical N input is crucial for reducing NH₃ volatilization.