Effects Of Biochar On N2_O Emissions And Soil Nitrification In Dryland Farming Ecosystem

Farmland soil is an important emission source of the nitrous dioxide(N2O). The oxidation of ammonium to nitrate nitrogen in low-carbon dry farmland soil is the main N2 O production process under aerobic conditions. Changes of soil environmental factors such as soil texture, moisture content, aeration, temperature, soil pH and soil nutrient status due to different soil management practices will impact the nitrification and N2 O emission in dry-land. Recently, with the deepening of scientific research, we found that biochar has a large surface area, high water holding and adsorption capacity; however, little study about whether biochar has a significant effect on N2 O emission characteristics of dry-land soil was found. We hypothesized that the biochar, as well as fertilization, would affect soil N2 O emission and nitrification in the dry-land ecosystem. Based on a long-term field experiment planted with spring maize on the Loess Plateau, five levels of the biochar amendment(0, 10, 20, 30, 50 t hm-2) under with different fertilization was included to explore effects of biochar on N2 O emission for two years(the year of 2014 and 2015). The closed static opaque chamber combined with the gas chromatograph was used to determine and analyze N2 O. Furthermore, an incubation experiment was conducted to analyze the effect of biochar on spring maize farmland N2 O emissions and soil nitrification. The aim of this paper is to provide a scientific basis for reasonable application of biochar to regulate farmlands N2 O emissions via accurate determination and possible factors analysis. The main conclusions are as follows:1. Without biochar-amendment, nitrogen application could significantly increase N2 O flux and cumulative N2 O emission in maize season and fallow season. Biochar decreased both N2 O flux and the cumulative N2 O emission(P<0.05); Difference among treatments was significantly affected by years. No significant difference was found among treatments with biochar on the N2 O flux and the cumulative N2 O emission in the fallow season.2. Nitrogen fertilization and biochar could increase spring maize yield in dry-land. During the two experiment years, yield of the C0N1(225 kg N hm-2+0 t hm-2 biochar) was significantly higher than that of C0N0(none nitrogen and none biochar)(P<0.05); The yield of C3N1 was the highest, significantly higher than those of C1N1 and C0N1. The N2 O warming potential(GWP) during the fallow season were all at low level, which was higher in nitrogen application treatments than none nitrogen application. Under the nitrogen application, treatments with biochar could decrease the GWP, greenhouse gas intensity(GHGI) and the emission factors(EF), especially C3N1 and C5N1 treatments.3. The ammonium and nitrate nitrogen concentrations of all treatments in the fallow season were at low and there was no significant difference among treatments. After applying nitrogen, the ammonium and nitrate nitrogen concentrations had same trend in the maize season of the year 2014 and 2015, achieving the highest level at days 5-7 and days 2-4, respectively. N2 O flux had a significant positive correlation with the ammonium and nitrate nitrogen of the soil layer of 0-20 cm(P<0.01), and had some positive correlation with the soil water capacity, while had no significant correlation with soil temperature with or without biochar. But the person of the N2 O flux with ammonium and nitrate nitrogen in the biochar treatment was lower than no biochar treatment, while the person of the N2 O flux with soil capacity was higher than no biochar treatment.4. On the whole, the nitrification efficiency and nitrification intensity in the 24 h incubation of the different layers at same growth period were different, following the order: 0-20 cm layer soil>20-40 cm layer soil>40-60 cm layer soil. As to growth periods, the nitrification efficiency and nitrification intensity of the 0-20 cm layer soil was in the order of V6>R3, R1, PT>R6. The difference of nitrification efficiency and nitrification intensity at 20-40 cm and 40-60 cm layers were smaller than that of 0-20 cm layer soil. Among different treatments, the nitrogen application(C0N1) was the highest, and no nitrogen(C0N0) was the lowest in the nitrification efficiency with significant difference. Though differences in temporal and spatial characteristics were found, the biochar tended to decrease the nitrification efficiency and nitrification intensity in the 24 h incubation in all.5. The relationship between nitrate nitrogenof the dry-land and the incubation time was in line with the Logistic growth pattern, and the equation had a significant correlation. To the different layers, soil potential nitrification of the 0-20 cm layer was significant higher than that of 20-40 cm layer soil and both of which were significant higher than 40-60 cm layer soil. As for the same growth period, soil potential nitrification of C0N0 treatment was significant lower than other treatments and C0N1 treatment was the highest. Soil potential nitrification would decrease with biochar rate, which was the lowest in C5N1 treatment. Correlation analysis showed a significant positive relation between the cumulative N2 O emission and nitrification intensity as well as soil potential nitrification, and had a significant relation between the cumulative N2 O emission and nitrification of 0-20 cm layer soil.The above results indicated that nitrogen application could significantly increase the soil nitrification and N2 O emissions of spring maize in growing season in the dry-land on the Loess Plateau. Biochar could decrease the soil nitrification, N2 O flux peak and the cumulative N2 O emission to some extent. In a word, biochar application could effectively control N2 O global warming potential and N2 O emission intensity.