Ammonia volatilization in winter wheat/summer maize rotation system of purple soil in hilly area of Central Sichuan Basin

Excess ammonia in the atmosphere causes a cascade of environmental and human health issues. In China, ammonia volatilization (AV) from applied nitrogen fertilizers is a major source of ammonia emission. Purple soils properties and the climatic conditions of the regions significantly increase the potential for nitrogen loss via AV. However, as compared with other intensive agricultural regions in China, few researches have focused on nitrogen loss in purple soils via AV. This paper discussed AV in winter wheat/summer maize rotation system of purple soil in hilly area of Central Sichuan Basin, in order to provide basic data on atmospheric carbon and nitrogen gas exchange in terrestrial ecosystems. It also contributed to ammonia emission inventory and emission reduction measures in croplands. The study was conducted in typical sloping croplands in the Central Sichuan Basin. AV processes in winter wheat/summer maize rotation system were monitored by a wind tunnel system. During every experimental period, there was only 1 treatment with 3 replicates. Wind speed and direction, air temperature and relative humidity, soil temperature, relative humidity, and others meteorological data were obtained from micro-weather stations in the field. Soil samples (from the 020 cm depth) were collected every 23 days and then mixed evenly before analysis for NH₄⁺-N. The results showed that due to deep placement of nitrogen fertilizer and lower temperature, the rate of loss of N via AV in winter wheat growing season was obviously less than that in maize growing season. AV loss in winter wheat growing season was 9.7 kg(N)hm^-2 in 2013 and 11.4 kg(N)hm^-2 in 2014, respectively, accounting for 7.4% and 8.8% of applied N. In maize growing season, banding fertilization followed by covering of soils was an effective way to reduce AV loss. The rate of loss N via AV during 3-leaf stage of summer maize in 2013 (broadcasting) and 2014 (banding) were 34.1% and 21.4%, respectively. It was extremely dry weathers before fertilization at 10-leaf stage period of maize in the summer of 2014. About 30 mm of irrigation water was immediately applied after urea spread application, and the highest AV loss occurred during this period. This was mainly due to the suitable soil water condition provided by irrigation water in extremely dry weathers. Therefore, it was necessary to avoid the application of nitrogen under dry soil conditions. The results suggested that in winter wheat/summer maize rotation system in the purple soil of hilly area of Central Sichuan Basin, AV loss in winter wheat growing season and summer maize growing season, respectively, accounted for (8.1±1.0)% and (32.8±1.8)% of the N application.