Effects of irrigation and nitrogen application on ammonia volatilization in solar greenhouse soils in winter-spring cucumber cultivation

Ammonia volatilization characteristics in fertilized and non-fertilized belts of greenhouse soils were investigated under different irrigation and nitrogen application treatments during winter-spring cucumber cultivation via the venting method. Also differences in ammonia volatilization among water-saving irrigation, reduced nitrogen treatment and traditional water/nitrogen treatments were analyzed and discussed. From the study, peak ammonia volatilization rate was on 7 days after basal fertilization in the solar greenhouse soil. Compared with traditional nitrogen treatment, the peak value for 25%-reduction in nitrogen fertilization dropped by 18.2%~34.3%. While peak ammonia volatilization rate was on the first day in the fertilization belt, it was on the fifth day in the non-fertilization belt after topdressing. Also compared with traditional treatments, the peak value for 25%-reduction in nitrogen fertilization also dropped by 12.3%~37.2% and that for water-saving irrigation treatment increased by 3.9%~47.0%. Ammonia volatilization and loss in the fertilization belt of greenhouse soils mainly occurred during cucumber blooming and initial fruiting periods, which were respectively 1.07~1.50 and 1.06~1.27 times those of the non-fertilization belt. No significant differences in ammonia volatilization and loss existed between fertilization and non-fertilization belts of greenhouse soils during cucumber full-fruit period and end-fruit periods. Ammonia volatilization rate increased with (0~10 cm) soil ammonium nitrogen content and improvement in (5 cm) soil temperature. However, a negative correlation existed between (0~10 cm) soil water content and ammonia volatilization rate. Cumulative ammonia volatilization was 11.4~26.6 kg·hm^-2 during the entire cucumber growth season. Compared with traditional nitrogen and irrigation treatments, cumulative ammonia volatilization in the 25%-reduction in nitrogen fertilization dropped by 20.8%~22.2%. Also water-saving irrigation treatments concurrently improved cumulative ammonia volatilization by 0~4.51%. The analysis showed that appropriate reductions in nitrogen fertilization significantly limited ammonia volatilization and enhanced irrigation/nitrogen fertilizer efficiency in solar greenhouse soils in Hebei Province. While water-saving also significantly improved irrigation/nitrogen fertilizer efficiency, it failed to significantly reduce ammonia volatilization. Irrigation water-use efficiency of the 25%-reduction in nitrogen fertilization improved by 2.6%~5.9% over traditional nitrogen treatment. Compared with traditional irrigation, agronomic efficiency of nitrogen in water-saving irrigation increased by 13.9%~75.0%.