3:1.5.1 Nitrogen in Rainfall

Lightning discharge converts atmospheric $N_2$ to nitric acid which can then be transferred to the soil with precipitation. The chemical steps involved are:

step 1: $N_2+O_2\xrightarrow{arc of electricity}2NO$ (monoxide)

step 2: $2NO+O_2\rightarrow NO_2$ (dioxide)

step 3: $3NO_2+H_2O\rightarrow 2HNO_2+NO$ (nitric acid and monoxide)

More nitrogen will be added to the soil with rainfall in areas with a high amount of lightning activity than in areas with little lightning.

The amount of nitrate added to the soil in rainfall is calculated:

3:1.5.1

where is nitrate added by rainfall (kg N/ha), is the concentration of nitrate in the rain (mg N/L), and is the amount of precipitation on a given day (mm HO). The nitrogen in rainfall is added to the nitrate pool in the top 10 mm of soil.

The amount of ammonia added to the soil in rainfall is calculated:

3:1.5.2

where is nitrate added by rainfall (kg N/ha), is the concentration of ammonia in the rain (mg N/L), and is the amount of precipitation on a given day (mm HO). The nitrogen in rainfall is added to the ammonia pool in the top 10 mm of soil.

Table 3:1-4: SWAT+ input variables that pertain to nitrogen in rainfall.