Effects of the Combined Application of Organic and Inorganic fertilizers on N2 O Emissions from Saline Soil

Abstract

Combining organic fertilizer with chemical fertilizer may affect the microbial processes related to nitrous oxide (N2O) emissions under different degrees of soil salinization. A mild saline soil (S1; electrical conductivity (EC) 0.46 dS·m-1) and moderate saline soil (S2; EC 1.07 dS·m-1) in the Hetao irrigation district of Inner Mongolia were selected. Under equal N rates, the study involved five treatments:U1 (240 kg·hm-2 of chemical fertilizer), U3O1 (180 kg·hm-2 of chemical fertilizer+60 kg·hm-2 of organic fertilizer), U1O1 (120 kg·hm-2 of chemical fertilizer+120 kg·hm-2 of organic fertilizer), U1O3 (60 kg·hm-2 of chemical fertilizer+180 kg·hm-2 of organic fertilizer), and O1 (240 kg·hm-2 of organic fertilizer). In addition, a blank control treatment (CK) was employed to investigate the effects of different fertilization treatments on the N2O emissions from the two saline soils. The results showed that the total N2O emissions from the S2 soil in the same treatment were between 11.86% and 47.23% higher than those from the S1 soil (P<0.05). the dynamic trend of the soil N2O fluxes among the different treatments were similar. The peak N2O emissions occurred after fertilization, and the N2O cumulative emission fluxes accounted for nearly 60% of the emissions during the entire growth period. The proper application of organic fertilizer could significantly reduce the soil N2O emission; the S1 and S2 saline soils treated with U1O1 and O1, respectively, had the lowest N2O emissions, whereby there were significant reductions of 33.62% and 28.51% in comparison to the U1 treatment (P<0.05). Moreover, higher maize yields could be obtained and the N2O flux was significantly positively correlated with the NH4+-N content (P<0.01) but negatively correlated with the NO3--N content. The results demonstrated that nitrification was the main way to produce N2O in the studied salinized maize farmland, and that the addition of organic fertilizer could reduce the N2O production by decreasing the soil NH4+-N content. Based on the changes in the corn yield and a reduction in the greenhouse effect, suitable organic and inorganic fertilizer management models for the Hetao irrigation area were the mild saline soil:120 kg·hm-2 of urea +120 kg·hm-2 of organic fertilizer), and the moderate saline soil:240 kg·hm-2 of organic fertilizer.