[Comprehensive Effects of the Application of Water and Fertilizer Amount on CO₂ Emission from Soils of Summer-maize...

Field experiments were conducted to determine the effects of water and fertilizer amount on soil CO₂ emissions by using the method of static chamber/gas chromatography in summer maize farmland ecosystem. Three factors (three irrigation levels including 90 mm, 76.5 mm and 63 mm, four nitrogen fertilizer levels including 300 kg·hm^-2, 255 kg·hm^-2, 210 kg·hm^-2 and 0 kg·hm^-2, and four phosphate fertilizer levels including 90 kg·hm^-2, 76.5 kg·hm^-2, 63 kg·hm^-2 and 0 kg·hm^-2) were designed in the experiment. The results showed that soil CO₂ emission under different water and fertilizer conditions showed obvious seasonal fluctuation, the main and secondary peak appeared at jointing to tasseling stage and tasseling to grouting stage. The soil CO₂ emissions were relevant to the supply levels of fertilizer and irrigation. In the high fertilizer F₁ (N 300 kg·hm^-2, P₂O₅ 90 kg·hm^-2) and low fertilizer F_0.7 (N 210 kg·hm^-2, P₂O₅ 63 kg·hm^-2) conditions, average soil CO₂ emissions flux during the whole growth period of high water W₁ (90 mm) was significantly higher than that of low water W_0.7 (63 mm); the difference of soil CO₂ emissions between medium water level W_0.85 (76.5 mm) and low water level was not significant under medium and low nutrient condition F_0.85 (N 255 kg·hm^-2, P₂O₅ 76.5 kg·hm^-2). Soil CO₂ emissions intensity of high fertilizer F₁ was significantly larger (by 14.82%) than that of low fertilizer F_0.7 under high water supply W₁ (P<0.05), and that of F_0.85 was significantly bigger (by 8.03%) than that of F_0.7 in the medium water supply(P<0.05), while the difference between treatments at low water level was not significant(P>0.05). Compared with nonfertilized treatment, soil CO₂ cumulative emissions of the whole growth period with application of nitrogen fertilizer (210 kg·hm^-2), phosphate fertilizer (63 kg·hm^-2) and nitrogen mixed with phosphate fertilizer (210 kg·hm^-2, 63 kg·hm^-2) were significantly increased by 23.70%, 19.00% and 12.30%, respectively. And interaction effects between nitrogen and phosphorus fertilizer were extremely significant (P<0.01). Variance analysis of the interaction of water and fertilizer showed that the average soil CO₂ fluxes of the whole growth period were not statistically significant but cumulative emissions of soil CO₂ were significant (P<0.05) when the difference of supply level was 15%. In addition, soil CO₂ flux and cumulative emission in the whole growth period were significant when supply differed by 30%. Obviously, soil CO₂ emissions were promoted significantly by application of irrigation amount, nitrogen fertilizer, phosphorus rate and water and fertilizer interaction, while it was inhibited by nitrogen mixed with phosphorus. It was effective to regulate soil CO₂ emission by water and fertilizer controlling measures.