Effects of various nitrogen fertilizers on emission of nitrous oxide from soils

Summary

Field studies of the effects of different N fertilizers on emission of nitrous oxide (N20) from three Iowa soils showed that the N₂O emissions induced by application of 180 kg ha⁻¹ fertilizer N as anhydrous ammonia greatly exceeded those induced by application of the same amount of fertilizer N as aqueous ammonia or urea. On average, the emission of N₂O-N induced by anhydrous ammonia was more than 13 times that induced by aqueous ammonia or urea and represented 1.2% of the anhydrous ammonia N applied. Experiments with one soil showed that the N₂O emission induced by anhydrous ammonia was more than 17 times that induced by the same amount of N as calcium nitrate. These findings confirm indications from previous work that anhydrous ammonia has a much greater effect on emission of N₂O from soils than do other commonly used N fertilizers and merits special attention in research relating to the potential adverse climatic effect of N fertilization of soils.

Laboratory studies of the effect of different amounts of NH₄OH on emission of N₂O from Webster soil showed that the emission of N₂O-N induced by addition of 100 μg NH₄OH-N g⁻¹ soil represented only 0.18% of the N applied, whereas the emissions induced by additions of 500 and 1 000 μg NH4OH-N g⁻¹ soil represented 1.15% and 1.19%, respectively, of the N applied. This suggests that the exceptionally large emissions of N₂O induced by anhydrous ammonia fertilization are due, at least in part, to the fact that the customary method of applying this fertilizer by injection into soil produces highly alkaline soil zones of high ammonium-N concentration that do not occur when urea or aqueous ammonia fertilizers are broadcast and incorporated into soil.