免耕稻田氮肥运筹对土壤NH3挥发及氮肥利用率的影响

Abstract

NH3volatilization is an important process of N loss from fertilizer nitrogen( N) applied to no-tillage rice fields.It has been demonstrated that no-tillage promotes NH3volatilization. However,few studies have been conducted to investigate the effects of N management on NH3volatilization from no-tillage paddy fields. Therefore,a field experiment was conducted on a clay loam soil( Anthrosol,World Reference Base for Soil Resources) to study the effects of N management on NH3volatilization and N use efficiency from no-tillage rice fields in the city of Wuxue in central China during the 2012rice-growing season. In this study,five experimental treatments were arranged in a completely randomized design with three replications. Five treatments were applied including five application rates of N fertilizer in the seedling,mid-tillering,flowering and heading stages of rice: 2∶2∶3∶3( R1),3∶2∶2∶3( R2),4∶2∶2∶2( R3),4∶3∶1∶2( R4) and 0∶0∶0∶0( CK). The NH3volatilization fluxes were determined 20 times using a venting method during the 2012 rice growing season. NH+4concentrations and pH of the soils and field surface water were also measured. The obtained results showed that application of N fertilizer significantly enhanced both NH+4concentrations of the soils and field surface water and the soil pH. Compared with the other fertilized treatments( R2,R3 and R4),R1 significantly decreased NH+4concentrations of the soils and field surface water. In the fertilized treatments,during the rice growing season,each application of N fertilizer led to NH3volatilization fluxes peaking after 1—3 days,and then dropping rapidly to those in the unfertilized treatment levels within1—2 weeks. The NH3volatilization fluxes in the CK treatment were relatively low,and remained nearly unchanged. The NH3volatilization fluxes ranged from 2. 0 to 21. 94 mg·m-2·d-1for the CK treatment and from 2. 21 to 209. 6 mg·m-2·d-1for the fertilized treatments. Mean NH3volatilization fluxes in the R1,R2,R3 and R4 treatments were( 13. 8±2. 0),( 15. 3±0. 2),( 15. 8± 0. 1) and( 14. 2 ± 0. 1) mg·m-2·d-1,respectively,which were 1. 57,1. 81,1. 88 and 1. 69 times,respectively,that in the CK treatment. The cumulative amounts of NH3volatilization were( 8. 52±0. 20)( CK),( 19. 59±2. 30)( R1),( 21. 85 ± 0. 68)( R2),( 21. 98 ± 0. 45)( R3) and( 23. 79 ± 1. 15) kg N / hm2( R4). For fertilized treatments,the highest cumulative NH3volatilization was observed at the mid-tillering stage( accounting for 11. 9% —14. 7% of the total),followed by the heading stage,with the minimum being found at the seeding and booting stages.Compared with no N fertilizer,application of N fertilizer significantly increased NH3volatilization by 56. 5% —64. 2% from the no-tillage paddy fields. In fertilized treatments,N losses through NH3volatilization accounted for 6. 2% —8. 5% of the applied N. Among the four fertilized treatments,the cumulative NH3volatilization was significantly reduced by 9. 1% —17. 7% under R1 than under the other fertilized treatments. Linear correlation analysis indicated that NH+4concentrations and pH in the soils and field surface water were significantly related to the NH3volatilization fluxes. Application of N fertilizer significantly affected N uptake of rice,where,compared with the CK treatments,fertilized treatments significantly increased N uptake of rice by 46. 5% —89. 3%. Compared with the other fertilized treatments,R1 significantly enhanced N use efficiency by 28. 4% —74. 9%. Therefore,our results suggest that N application at the late growth stage of rice can decrease NH3volatilization,thus improving N use efficiency of rice under no-tillage rice fields.