Effects of different water and nitrogen management on ammonia volatilization in pear orchard soil

Conventional pear tree fertilization and management results in fertilizer waste, environmental contamination and other problems. The long-term goal of farmland managers is to use soil water and fertilizers efficiently to improve crop yield. In this study, the dynamic box method was used to analyze changes in the soil ammonia volatilization rate, loss, and the physical and chemical properties under different water and nitrogen management regimes in the pear topdressing period in the orchard demonstration base of Jinzhou City, Hebei Province, from March to September 2019. The experiment had five treatments: blank (CK, no fertilization with conventional irrigation), compound fertilizer broadcasting and conventional irrigation (BW1), rhizosphere injection (20 cm deep) of liquid fertilizer and conventional irrigation (IW1), compound fertilzer broadcasting and 70% conventional irrigation (BW2), rhizosphere (20 cm deep) injection of liquid fertilizer and 70% conventional irrigation (IW2). The volatilization of ammonia in each treatment was the most severe in the first four days after fertilization. Two treatments of compound fertilizer broadcasting (BW1 and BW2) were especially severe, the peak variation range was 1.5−7.5 kg·hm⁻²·d⁻¹. Two treatments of rhizosphere injection of liquid fertilizer (IW1 and IW2) steadily changed with time, the peak range was 0.1−5.0 kg·hm⁻²·d⁻¹. The volatile loss of ammonia in the BW1, IW1, BW2, and IW2 treatments was 24.05 kg·hm⁻², 8.43 kg·hm⁻², 31.94 kg·hm⁻², and 14.06 kg·hm⁻², respectively; compared with BW1 (traditional management), the emission reduction rates of rhizosphere injection of liquid fertilizer (IW1 and IW2) was 64.95% and 41.54%, respectively. Ammonia volatilization was significantly affected by the irrigation amount, and rhizosphere injection fertilization significantly reduced ammonia volatilization emission and was less affected by the irrigation amount. Correlation analysis showed that ammonia volatilization was positively correlated with the soil ammonium nitrogen content and pH, but negatively correlated with the soil nitrate nitrogen content. The correlation between ammonium nitrogen and nitrate nitrogen was highly significant (P<0.01). Soil moisture was positively correlated with ammonium nitrogen content (P<0.01). Compared with traditional management methods, the combination of rhizosphere injection fertilization and water-saving irrigation is an effective way to reduce nitrogen loss in orchards.