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,
|                                                  |                       |        |                     
|                                                  | 2006                  | 2005   |                     
|                                                  |                       |        |                     
|                                                  | (dollars in millions)
|                                                 
|EARNINGS:                                         |                      
|Net income                                        | $133.7                | $129.6 |                     
|Income taxes                                      | 65.6                  | 74.8   |                     
|                                                  |                       |        |                     
|Income before income taxes                        | 199.3                 | 204.4  |                     
|Fixed charges as defined                          | 53.9                  | 56.7   |                     
|                                                  |                       |        |                     
|Total earnings as defined                         | $253.2                | $261.1 |                     
|                                                  |                       |        |                     
|                                                 
|FIXED CHARGES:                                   
|Interest expense                                  | $52.8                 | $53.3  |                     
|Estimated interest component of rent expense      | 1.1                   | 3.4    |                     
|                                                  |                       |        |                     
|Total fixed charges as defined                    | $53.9                 | $56.7  |                     
|                                                  |                       |        |                     
|Ratio of Earnings to Fixed Charges (Unaudited)    | 4.70                  | 4.60   |                     
|                                                  |                       |        |                     
|Preferred dividend requirements (pre-tax basis) * | $17.1                 | $18.1  |                     
|                                                  |                       |        |                     
|Fixed charges and preferred dividend requirements | $71.0                 | $74.8  |                     
|                                                  |                       |        |                     
|Ratio of Earnings to Combined Fixed Charges and  
|Preferred Dividend Requirements (Unaudited)       | 3.57                  | 3.49   |                     
|                                                  |                       |        |                     

* 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.