Intensification of agriculture has made great contributions to food production over the past 50 years. While, much of the progress in food production has resulted from the significant increase in the use of chemical nitrogen fertilizers (Zhu and Chen, 2002). About 15% of the total nitrogen fertilizers used in agriculture are applied to rice production alone, but the nitrogen utilization rate of paddy fields is only 30%-35% in China (Heffer, 2009; Yang et al., 2020). Ammonia (NH3) volatilization is one of the major pathways for nitrogen loss in agricultural systems worldwide. Ammonia emissions from agricultural systems account for about 2/3 of total atmospheric ammonia emissions (IPCC, 2019). Studies have shown that up to 60% of nitrogen can be lost through ammonia volatilization (Pan et al., 2016; Wang et al., 2021), and the global ammonia emissions from fertilizers was 9.0 Tg N per year (Erisman et al., 2007). Volatilized NH3 results in increased nitrogen loads to the environment through the processes of atmospheric transportation and deposition, which contributes to many environmental problems and also damage human health due to secondary aerosols or particle formation (Krupa, 2003; Cameron, et al., 2013; Li, et al., 2017). Therefore, it is of great significance to reduce ammonia volatilization in agricultural system to protect ecological environment, maintain sustainable development of agriculture and reduce threats to human health.
The amount of NH3 volatilization increases with increasing nitrogen applied in both paddy and dry fields (Yu, et al., 2012; Zheng et al., 2018). That is because all of the factors that can shift the chemical equilibrium, NH4+ (exchangeable) <=> NH4+ (liquid phase) <=> NH3 (gaseous phase) <=> NH3 (atmosphere), to the right will promote NH3 volatilization (Song and Fan, 2003). In addition to the amount of fertilizer applied, ammonia volatilization is affected by cultivation and management measures such as fertilization period, fertilizer type, irrigation method, straw mulching, environmental conditions such as temperature and light, and physical and chemical properties such as carbon and nitrogen content, and pH value (Pan et al., 2016; Zhou, et al., 2016; Zhang, et al., 2022). In different cropping systems, water and fertilizer management measures and growth period were different for various crops, which lead to changes in soil properties and environmental conditions, thus affecting ammonia volatilization and nitrogen use efficiency of the cropping system. While, the effect of different cropping systems on ammonia volatilization is seldom reported so far.
Paddy-upland cropping systems is a good choice for the major grain-producing areas and has become more popular in recent years to ensure global food security in the case of continuous decrease of arable land and increasing population, especially for Asia (Zheng et al., 2016; Zhou et al., 2014). Due to its high economic profitability, the planting area of vegetable-rice rotation is getting larger and larger. Garlic (Allium sativum L.)-rice rotation (GR) is one of the typical representatives. Garlic, a well-known spice and seasonal vegetable, the global planting area of which exceeded 1.6×106 hectares, and more than 50% was in China (FAO, 2010–2020). Large amount of fertilizer input combined with straw mulching is the key to high yield of garlic. Cui et al. (2015) showed that the optimal application rate N、P2O5、K2O for garlic was as high as 436.95、213.34、336.74 kg·ha− 1, respectively. In consequence, previous studies of GR mainly focus on the effects of fertilization management and straw mulching on crop yield, total nitrogen and phosphorus loss (Amoli 2012; Islam et al., 2015; Yao et al., 2017). Our previous results showed that a large amount of nitrogen fertilizer applied in garlic season would remain in the soil and improve the soil nitrogen level of rice season (Zhou et al., 2020). However, GR could reduce greenhouse gas emissions, such as N2O and CH4, compared with WR (Wang et al., 2022). Therefore, we hypothesized that ammonia volatilization in paddy field under GR with higher soil nitrogen level would also be reduced. In this research, the fields where GR and WR were cultivated for many years were studied. Wheat-rice rotation (WR), plays a very important role in grain production in the world and has a long history from the tang dynasty in China (Fan et al., 2008), with significantly less nitrogen fertilizer input in what than garlic, was used as a control in this study. The main objectives of this research were to (i) study the differences and characteristics of NH3 volatilization in paddy under WR and GR, (ii) find the key factors that influencing NH3 volatilization, thus to provide reference for putting forward some reasonable cultivation and management measures to reduce NH3 volatilization and environmental risks, and contribute to the cleaner production in paddy.