1. Strategies for mitigating ammonia emissions from agroecosystems
Baobao Pana, Shu Kee Lama, Arvin Mosiera, Yiqi Luob, Deli Chena
a Crop and Soil Science Section, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Victoria 3010, Australia
bDepartment of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, 73019, USA *
Introduction
Ammonia (NH3) volatilization is one of the main pathways of N loss in agricultural systems, and is conducive to low fertilizer N use efficiency, environmental and health issues, and indirect nitrous oxide emission. While studies on the mitigation strategies for NH3 emission are sometimes inconclusive, a systematic synthesis of these studies is lacking.
A meta-analysis of the current literature on the mitigation strategies of NH3 volatilization can provide critical information on how to minimize N loss as NH3 in agricultural systems. The information is critical for improving global fertilizer N use efficiency, environmental quality, and climate change mitigation.
Objectives
The objectives of this analysis were (i) to provide and evaluate the effectiveness of mitigation strategies for NH3 volatilization from synthetic fertilizers applied in agricultural systems; and (ii) to provide critical information for global N management in agricultural systems, environmental quality and climate change mitigation.
Table 1 Nitrogen loss as NH3 of applied urea from agricultural land worldwide
Continent
N loss as NH3 %
kg N ha–1 per cropping season
Mean
Range
East Asia
15.9
1.7–48.0
20.6
1.8–96.0
South Asia
30.7
3.0–56.7
37.5
5.6–69.7
Southeast Asia
16.1
14.4–19.5
10.7
8.6–14.6
Australasia
16.0
2.0–30.0
13.7
0.8–49.2
Europe
13.0
0.9–29.8
17.0
0.6–29.8
North America
17.5
0.6–64.0
22.2
0.6–89.6
South America
14.2
1.7–31.8
11.8
0.9–25.4
Average
17.6
0.9–64.0
19.1
0.6–96.0
Materials and methods
Mitigation strategies: irrigation, N application method (deep placement), fertilizer type (ammonium-based vs. urea) and the use of urease inhibitors and controlled release fertilizers.
145 studies; 824 direct comparisons (from 1971 to April 2016 )
Response metric: natural log of the response ratio (response to treatment/response to control)
Weighting by replication
Results
Percentage of N loss as NH3
Globally, the average NH3 volatilization losses ranged from 0.9 to 64% (a mean of 17.6%) of the applied N. (Table 1).
The percentage of N loss as NH3: South Asia> North America> Southeast Asia> Europe (Table 1).
Effect of the 4R nutrient stewardship on NH3 volatilization
non-urea based and urea-containing mixed fertilizers decreased NH3 loss by 75% and 31%,respectively (Fig. 1a).
Ammonia loss increased with N application rate (Fig. 1b).
Split frequency had no effect on ammonia loss (Fig. 1c).
Deep placement decreased 55% ammonia (Fig. 1d).
Figure 2. Effect of (a) irrigation, (b) residue retention and (c) amendment on NH3 volatilization. Means and 95% confidence intervals are depicted. Numbers of experimental observations are in parentheses.
Figure 1. Effects of (a) fertilizer type, (b) factor relative to the lowest N rate, (c) split frequency and (d) deep placement on NH3 volatilization. Means and 95% confidence intervals are depicted. Numbers of experimental observations are in parentheses.
Effect of farming practices on NH3 volatilization
Irrigation decreased NH3 volatilization by 35% compared to rainfed or supplementary (minimal) irrigation (Fig. 2a).
Residue retention increased NH3 volatilization by 26% (Fig. 2b).
Amendments reduced NH3 loss by 31% (zeolite, 44%; pyrite, 21%; organic acid, 16%) (Fig. 2c).
Effect of enhanced efficiency fertilizers
Urease inhibitors and controlled release fertilizers reduced NH3 volatilization by 54% and 68%, respectively (Fig. 3a,b).
Nitrification inhibitors increased NH3 volatilization by 38% (Fig 3c).
Potential for climate change mitigation
Adopting various NH3 mitigation strategies (reduction of 16–88%, Figs. 1–3) would decrease emission of 15–81 million tons CO2-e annually from agricultural systems.
Figure 3. Effect of (a) urease inhibitors, (b) controlled release fertilizers and (c) nitrification inhibitors on NH3 volatilization. Means and 95% confidence intervals are depicted. Numbers of experimental observations are in parentheses.
Conclusions
Mitigating NH3 loss from agriculture is important. Various strategies effectively decrease the loss.
The use of non-urea based fertilizers, reduced fertilizer application rate, deep placement of fertilizers, irrigation, urease inhibitors and controlled release fertilizers are effective in reducing NH3 volatilization by local level practicality when implemented. .
Our results provide major implications for global N management in agricultural systems, environmental quality and climate change mitigation.
For further details，
Pan, B., Lam, S. K., Mosier, A., Luo, Y., & Chen, D. (2016). Ammonia volatilization from synthetic fertilizers and its mitigation strategies: A global synthesis. Agriculture, Ecosystems & Environment, 232,