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

|                                                    | Nine Months           |      |                     
|--------------------------------------------------- | --------------------- | ---- | --------------------
|                                                    | Ended Sep. 30,        |      | Years Ended Dec. 31,
|                                                    |                       |      |                     
|                                                    | 2008                  | 2007 |                     
|                                                    |                       |      |                     
|                                                    | (dollars in millions)
|EARNINGS:                                           |                       |      |                     
|Net income                                          |                       | $112 | .8                  
|Income taxes (a)                                    |                       | 46   | .9                  
|                                                    |                       |      |                     
|Income before income taxes                          |                       | 159  | .7                  
|                                                   
|Fixed charges as defined                            |                       | 45   | .7                  
|                                                    |                       |      |                     
|Total earnings as defined                           |                       | $205 | .4                  
|                                                    |                       |      |                     
|FIXED CHARGES:                                      |                      
|Interest expense                                    |                       | $44  | .2                  
|Estimated interest component of rent expense        |                       | 1    | .5                  
|                                                    |                       |      |                     
|Total fixed charges as defined                      |                       | $45  | .7                  
|                                                    |                       |      |                     
|Ratio of Earnings to Fixed Charges                  |                       | 4    | .49                 
|                                                    |                       |      |                     
|Preferred dividend requirements (pre-tax basis) (b) |                       | $16  | .3                  
|                                                    |                       |      |                     
|Fixed charges and preferred dividend requirements   |                       | $62  | .0                  
|                                                    |                       |      |                     
|Ratio of Earnings to Combined Fixed Charges and     |                      
|Preferred Dividend Requirements                     |                       | 3    | .31                 
|                                                    |                       |      |                     

(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.