Effects of irrigation and nitrogen application on ammonia volatilization loss from vegetable fields under greenhouse cultivation

【Objectives】 Excessive nitrogen fertilization and irrigation are common phenomena in greenhouse cultivated vegetable production in China. Objectives of this study were to identify characteristics of soil ammonia volatilization under different irrigation and nitrogen conditions, and to investigate impacts of important factors on soil ammonia volatilization in a cucumber-tomato rotation system. 【Methods】 The study was carried out with two irrigation levels, traditional irrigation (W1) and reduced irrigation quantity (W2), and three nitrogen application rates, traditional nitrogen rate (N2), reduced by 25% from traditional nitrogen rate (N1) and no nitrogen application (N0). There were six treatments, W1N0, W1N1, W1N2, W2N0,W2N1 and W2N2. The venting method was used to investigate the dynamics of ammonia volatilization and the key impact factors related to soil ammonia volatilization in the vegetable fields in the North China Plain. 【Results】 The nitrogen rates have significant effect on the ammonium nitrogen contents of topsoil (0-10 cm depth) in the cucumber-tomato rotation system. Compared to the traditional nitrogen treatment (N2), the peak value of the ammonium nitrogen concentration is reduced by 25.1%-30.3% (P0.05) in the reduced nitrogen treatment (N1) under the same irrigation condition. Reduction of the nitrogen rate significantly reduces the soil ammonia volatilization rate. Compared to the traditional nitrogen treatment (N2), the average rates of soil ammonia volatilization are reduced by 21.1%-22.8% (P0.05) and 16.5%-17.9% (P0.05) in the cucumber growing season and tomato growing season, respectively. The ammonia volatilization amount and loss ratio of the nitrogen fertilizer are 17.8-48.1 kg/hm2 and 1.23%-1.44% in the cucumber-tomato rotation system, respectively. Compared to the N2 treatment, the ammonia volatilization amount and loss ratio of the nitrogen fertilizer of the N1 treatment are reduced by 19.3%-20.0% (P 0.05) and 0.85-0.92 percentage point, respectively. There is a significantly positive correlation between the soil ammonia volatilization rate and 0-10 cm soil ammonium nitrogen concentration, which shows that the 0-10 cm soil ammonium nitrogen concentration is one of the important factors affecting soil ammonia volatilization. The soil ammonia volatilization rate and ammonia volatilization amount in the reduced irrigation treatment (W2) are higher than those in the traditional irrigation treatment (W1) (P0.05). Appropriate reduction of the nitrogen fertilizer and irrigation application not only has high vegetable production, but also significantly increases the irrigation water and nitrogen use efficiencies. Compared to the N2 treatment, the nitrogen agronomic efficiency is increased by 95.4%-146.4% in the N1 treatment, and compared to the W1 treatment, the irrigation water agronomic efficiency of the W2 treatment is increased by 27.7%-54.0%. 【Results】 By taking the reasonable measure of water-saving and nitrogen application reduction, the objectives of reducing the ammonia volatilization, increasing the yield and improving the irrigation water and nitrogen use efficiencies can be achieved. In summary, the combination of water-saving irrigation by 30% and nitrogen fertilizer reduction by 25% (W2N1) can make a good economic benefit and environmental effect in this experiment.