Exhibit 12.2

INTERSTATE POWER AND LIGHT COMPANY

|RATIO |  | OF
EARNINGS TO FIXED CHARGES AND RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND
PREFERRED DIVIDEND REQUIREMENTS
|----- |  | ----------------------------------------------------------------------------------------------------------------

|                                                    | Three Months          |     
|--------------------------------------------------- | --------------------- | ----
|                                                    | Ended March 31,       |     
|                                                    |                       |     
|                                                    | 2008                  | 2007
|                                                    |                       |     
|                                                    | (dollars in millions)
|EARNINGS:                                           |                       |     
|Net income                                          |                       | $29 
|Income taxes (a)                                    |                       | 16  
|                                                    |                       |     
|Income before income taxes                          |                       | 45  
|                                                    |                      
|Fixed charges as defined                            |                       | 14  
|                                                    |                       |     
|Total earnings as defined                           |                       | $60 
|                                                    |                       |     
|FIXED CHARGES:                                      |                      
|Interest expense                                    |                       | $14 
|Estimated interest component of rent expense        |                       | 0   
|                                                    |                       |     
|Total fixed charges as defined                      |                       | $14 
|                                                    |                       |     
|Ratio of Earnings to Fixed Charges                  |                       | 4   
|                                                    |                       |     
|Preferred dividend requirements (pre-tax basis) (b) |                       | $6  
|                                                    |                       |     
|Fixed charges and preferred dividend requirements   |                       | $20 
|                                                    |                       |     
|Ratio of Earnings to Combined Fixed Charges and     |                      
|Preferred Dividend Requirements                     |                       | 2   
|                                                    |                       |     

(a) Includes net interest related to
unrecognized tax benefits.

(b) Preferred dividend requirements
(pre-tax basis) are computed by dividing the preferred dividend requirements by one
hundred percent minus the respective year-to-date effective income tax rate.