ABSTRACT
Focusing on typical mildly saline soil, S1 (EC, 0.62 dS·m-1), and moderately saline soil, S2 (EC, 1.17 dS·m-1), in Hetao Irrigation District of Inner Mongolia, the response of nitrification and denitrification process to salinization degree and the proportion of organic and inorganic nitrogen application were studied. The experimental treatments consisted of(1) no nitrogen(CK), (2) only inorganic nitrogen(U1), and(3) organic nitrogen(U3O1, U1O1, U1O3, and O1) compared to 25%, 50%, 75%, and 100% inorganic nitrogen. The results showed that increasing salinity reduced the soil nitrification potential and increased the soil denitrification capacity. The soil nitrification potential of the S1 soil was 28.81%-69.67% higher than that of the S2 soil, while the denitrification capacity was reduced by 17.16%-88.91%. With an increase in salinity, the AOB abundance and nitrification contribution rate were reduced, but the AOA abundance and nitrification contribution rate were increased. Furthermore, an increase in salinity increased the abundance of nirK and nirS bacteria, and increased N2O/(N2O+N2) production, but reduced the abundance of nosZ. In the S1 soil, the nitrification potential and denitrification capacity of U1O1 were highest, increasing by as much as 18.59% and 15.87%, respectively, compared to the U1 treatment. In the S2 soil, the difference in the soil nitrification potential between the various fertilization treatments was not significant, and the denitrification capacity of the O1 treatment was highest. The S1 and S2 saline soils treated with U1O1 and O1, respectively, had higher AOB gene abundance and nitrification contribution rates, increased nirS and nosZ gene abundances, and significantly reduced N2O/(N2O+N2) product ratios. Our findings suggested that mildly saline soils(120 kg·hm-2 urea+120 kg·hm-2 organic fertilizer) and moderately saline soils(240 kg·hm-2 organic fertilizer) are more conducive to soil nitrification and denitrification processes compared to soils to which inorganic nitrogen is applied alone.
