Interactive effects of nitrogen fertilizer sources and soil acidity on ammonia volatilization

Introduction while more than 2 million tones of nitrogen fertilizers is annually used in Iran (FAO, 2011: Motasharrezadah et al., 2015), it is documented that just only 20 percent of applied nitrogen fertilizers is uptaken in some wheat farms of Iran (Karimizarchi, 2015). In other words, around 80 percent of nitrogen fertilizers are lost through leaching and volatilization, which increases the potential of environmental contamination with increase N input expenditure of the farmer, or stored in the soil. So the present study was aimed to quantify the role of ammonia volatilization from Iranian soils and to introduce simple as well as helpful techniques for ammonia volatilization reduction in Iranian wheat farms. Materials and methods Firstly, a modified closed dynamic air flow system was provided. Soil materials were provided from tea research institute located in Lahijan, Iran as well as National Salinity Research station located in Ashkezar province, Yazd, Iran. The soils with three levels of acidity (7.88, 6.5 and 7.88) were incubated with 5 sources of nitrogenous fertilizers including ammonium sulphate, ammonium nitrate, urea, sulphur coated urea and potassium nitrate for 22days. Daily and cumulative volatilized ammonium was collected in 20 ml of 2% boric acid indicator solution and it was titrated with 0.01 N HCl. The analysis of variance for different parameters was done following ANOVA technique. When F was significant at p ≤ 0.05 level, treatment means were separated using DMRT. Results and discussion the results showed that soil acidity, fertilizer source and their interactions had significant effect on total volatilized nitrogen, maximum volatilized rate and day of highest volatilization rate. Total volatilized nitrogen depends on nitrogen fertilizer source and soil acidity. The results showed that more than 59 percent of applied ammonium sulphat at soil with the pH value of 7.88 lost through ammonia volatilization and resulted in air pollution. The volatalized nitrogen for sulphur coated urea and potassium nitrate equalled to 7.6 and 0.018 percent while that of ammonium nitrate and urea equalled to 49 percent. The results showed that potassium nitrate had the minimum cumulative ammonium volatilization of less than 0.07 mg N and it was not affected by soil acidity. In addition, our results proved that soil pH reduction from 7.88 to 6.5, reduced total ammonia volatilization for ammonium sulphate and nitrate from 227.15 and 189.82 to 2.39 and 0.99 mg N, respectively. Total volatilized nitrogen from ammonium sulphate and nitrate from soil with the pH of 4.5 were 2.51 and 1.33 mg N, respectively. While soil pH reduction from7.88 to 4.5 from soils treated with urea reduced ammonia volatilization from 188 to 157, this increased ammonia volatilization from sulphur coated urea from 29.2 to 87.05 mg N. In other words, our results proved that increasing soil pH resulted in significant decrease in total volatilized ammonia from sulphur coated urea. The total volatilized nitrogen from soils with the pH values of 4.5, 6.55 and 7.88 was equal to 22, 20 and 6 percent of applied sulphur coated urea. Maximum volatilized rate of ammonium was affected by soil pH and fertilizer sources. With decreasing soil pH the maximum volatilization rate from urea fertilizer was increase. The similar trend was found for sulphur coated urea. However, the maximum volatilization rate from ammonium nitrate and sulphate increased with soil pH increase. Interestingly, soil pH had not significant effect on maximum volatilized rate from potassium nitrate fertilizer and it was equal to 0.04 mg N per day. Conclusion As ammonia volatilization depends on nitrogen source, it is possible to decrease ammonia loss by selecting proper nitrogen fertilizer source. The results demonstrated that potassium nitrate had minimum ammonia loss and can be introduced as the optimum source of nitrogen fertilizer for a wide range of soil pH from 4.5 to 7.88. Ammonium nitrate and ammonium sulphate fertilizers had the least ammonia loss at soils with pH of 6.55 and less. However, sulphur coated urea had the least ammonia loss at soil pH of 7.88 and more.