Effects of polyurea-formaldehyde on ammonia volatilization and yields under rice−wheat rotation in Taihu Region

Objectives The aims of this study were to assess the effects of polyurea-formaldehyde slow-release fertilizer (MU) on NH₃ volatilization and grain yield in rice-wheat rotation in Taihu Region.

Methods A field trial was conducted under rice-wheat rotation system in Taihu Region.The tested polyurea-formaldehyde were MU70 (N 39%) and MU50 (N 40%), the soil was gleyed paddy soil. Using urea as control, six treatments were setup as 100%MU50, 100%MU70, 50%MU50, 50%MU70, farmer’s N practice (U) and control (CK). Except control, the total N application rate was N 270 kg/hm² for rice and 190 kg/hm² for wheat in all the treatments. All the fertilizers in MU were basal applied, and the urea was topdressed in three times for both rice and wheat. NH₃ volatilization was measured by a dynamic chamber method. At harvest, the yield and nitrogen uptakes were measured, and the economic profits were calculated.

Results NH₃ volatilization occurred primarily during the rice season rather than the wheat season. Application of slow-release fertilizer in the rice season significantly reduced NH₃ volatilization. The daily fluxes of NH₃ volatilization were positively correlated with floodwater ammonium concentrations. Compared to polyurea-formaldehyde, urea significantly increased the floodwater ammonium concentrations. 100%MU50 and 100%MU70 significantly reduced rice yield. However, 50%MU50 and 50%MU70 increased rice yield by 5.7%−3.2% compared with urea. In the wheat reason, 100%MU50 and 100%MU70 significantly decreased NH₃ volatilization and yield compared to urea. The NH₃ volatilization difference between 50%MU50 and urea was not significant, but both of them were lower than that of 50%MU70. Compared to the U treatment, 50%MU50 and 50%MU70 increased the NUE but 100%MU50 and 100%MU70 reduced NUE in both rice and wheat seasons. In addition, NUE in 50%MU50 was increased by 8.1% compared to the urea application in rice reason and the 50%MU70 significantly increased the NUE by 3% in wheat reason.

Conclusions Considering the agronomic, environmental and economic benefits, the total net income of 50%MU50 is 30259 yuan/hm², which is not significantly different from the treatment of urea (30168 yuan/hm²). Therefore, the 50%MU50 treatment is a promising option and deserves promotion in Taihu Region.