Gross nitrogen transformations and N2O emission sources in sandy loam and silt loam soils

The soil type is a key factor influencing N (nitrogen) cycling in soil; however, gross N transformations and N2O emission sources are still poorly understood. In this study, a laboratory N-15 tracing experiment was carried out at 60% WHC (water holding capacity) and 25 degrees C to evaluate the gross N transformation rates and N2O emission pathways in sandy loam and silt loam soils in a semiarid region of Heilongjiang Province, China. The results showed that the gross rates of N mineralization, immobilization, and nitrification were 3.60, 1.90, and 5.63 mg N/(kg center dot d) in silt loam soil, respectively, which were 3.62, 4.26, and 3.13 times those in sandy loam soil, respectively. The ratios of the gross nitrification rate to the ammonium immobilization rate (n/i(a)) in sandy loam soil and silt loam soil were all higher than 1.00, whereas the n/i(a) in sandy loam soil (4.36) was significantly higher than that in silt loam soil (3.08). This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil, and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO3- leaching. Under aerobic conditions, both nitrification and denitrification made contributions to N2O emissions. Nitrification was the dominant pathway leading to N2O production in soils and was responsible for 82.0% of the total emitted N2O in sandy loam soil, which was significantly higher than that in silt loam soil (71.7%). However, the average contribution of denitrification to total N2O production in sandy loam soil was 17.9%, which was significantly lower than that in silt loam soil (28.3%). These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.

Automated summary

Soil type significantly influences N cycling and N2O emissions, with silt loam soil having better N retention and release capabilities compared to sandy loam soil. Nitrification is the dominant pathway for N2O emissions, especially in sandy loam soil, while denitrification also contributes, particularly in silt loam soil.