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

|                                                    | Six Months            |                     
|--------------------------------------------------- | --------------------- | --------------------
|                                                    | Ended June 30,        | Years Ended Dec. 31,
|                                                    |                       |                     
|                                                    | 2007                  | 2006                
|                                                    |                       |                     
|                                                    | (dollars in millions)
|EARNINGS:                                           |                       |                     
|Net income                                          |                       | $53.2               
|Income taxes (a)                                    |                       | 31.4                
|                                                    |                       |                     
|Income before income taxes                          |                       | 84.6                
|                                                   
|Fixed charges as defined                            |                       | 33.4                
|                                                    |                       |                     
|Total earnings as defined                           |                       | $118.0              
|                                                    |                       |                     
|FIXED CHARGES:                                      |                      
|Interest expense                                    |                       | $32.6               
|Estimated interest component of rent expense        |                       | 0.8                 
|                                                    |                       |                     
|Total fixed charges as defined                      |                       | $33.4               
|                                                    |                       |                     
|                                                   
|Ratio of Earnings to Fixed Charges                  |                       | 3.53                
|                                                    |                       |                     
|                                                   
|Preferred dividend requirements (pre-tax basis) (b) |                       | $12.2               
|                                                    |                       |                     
|Fixed charges and preferred dividend requirements   |                       | $45.6               
|                                                    |                       |                     
|Ratio of Earnings to Combined Fixed Charges and     |                      
|Preferred Dividend Requirements                     |                       | 2.59                
|                                                    |                       |                     

(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.