免耕稻田氮肥运筹对土壤NH3挥发及氮肥利用率的影响

通过大田试验,设置5种不同的施肥比例(基肥:分蘖肥:拔节肥:穗肥-2:2:3:3(R1)、3:2:2:3(R2)、4:2:2:2(R3)、4:3:1:2(R4)与0:0:0:0(CK)),研究氮肥运筹对稻田NH₃挥发和氮肥利用率的影响。结果表明,(1)相对于不施肥,施肥显著提高了稻田NH₃挥发量。氮肥施用后,NH₃挥发损失量占施氮量的6.2%-8.5%,其中,以分蘖期NH₃挥发损失量最大,齐穗期次之,苗期和拔节期最小。施肥处理间,处理R1稻田累积NH₃挥发量最小,显著低于其它施肥处理,比处理R2、R3和R4分别低9.1%(P<0.05)、10.9%(P<0.05)和17.7%(P<0.05)。(2)相关分析表明,田面水NH₄⁺、pH值和土壤NH₄⁺和pH值均与稻田土壤NH₃挥发通量呈显著或者极显著相关;(3)处理R1水稻氮肥利用率相对于处理R2、R3和R4增加了28.4%(P<0.05)、55.4%(P<0.05)和74.9%(P<0.05)。研究表明,氮肥后移能有效降低免耕稻田NH₃挥发,提高水稻的氮肥利用率。

Effects of nitrogen management on NH3 volatilization and nitrogen use efficiency under no-tillage paddy fields

NH₃ volatilization 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 NH₃ volatilization. However, few studies have been conducted to investigate the effects of N management on NH₃ volatilization 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 NH₃ volatilization and N use efficiency from no-tillage rice fields in the city of Wuxue in central China during the 2012 rice-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 NH₃ volatilization fluxes were determined 20 times using a venting method during the 2012 rice growing season. NH₄⁺ concentrations and pH of the soils and field surface water were also measured. The obtained results showed that application of N fertilizer significantly enhanced both NH₄⁺ concentrations of the soils and field surface water and the soil pH. Compared with the other fertilized treatments (R2, R3 and R4), R1 significantly decreased NH₄⁺ concentrations of the soils and field surface water. In the fertilized treatments, during the rice growing season, each application of N fertilizer led to NH₃ volatilization fluxes peaking after 1-3 days, and then dropping rapidly to those in the unfertilized treatment levels within 1-2 weeks. The NH₃ volatilization fluxes in the CK treatment were relatively low, and remained nearly unchanged. The NH₃ volatilization fluxes ranged from 2.0 to 21.94 mg·m^-2·d^-1 for the CK treatment and from 2.21 to 209.6 mg·m^-2·d^-1 for the fertilized treatments. Mean NH₃ volatilization 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 NH₃ volatilization 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 NH₃ volatilization 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 NH₃ volatilization by 56.5%-64.2% from the no-tillage paddy fields. In fertilized treatments, N losses through NH₃ volatilization accounted for 6.2%-8.5% of the applied N. Among the four fertilized treatments, the cumulative NH₃ volatilization was significantly reduced by 9.1%-17.7% under R1 than under the other fertilized treatments. Linear correlation analysis indicated that NH₄⁺ concentrations and pH in the soils and field surface water were significantly related to the NH₃ volatilization 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 NH₃ volatilization, thus improving N use efficiency of rice under no-tillage rice fields.