<PAGE>

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   FORM 10-K/A
                                (Amendment No. 1)

                  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

                   For the fiscal year ended December 31, 2001
                         Commission file number: 1-8520

                              TERRA INDUSTRIES INC.
             (Exact name of registrant as specified in its charter)

                                    Maryland
                         (State or other jurisdiction of
                         incorporation or organization)

                                   52-1145429
                                (I.R.S. Employer
                               Identification No.)

                                  Terra Centre
                                600 Fourth Street
                                  P.O. Box 6000
                                Sioux City, Iowa
                    (Address of principal executive offices)

                                   51102-6000
                                   (Zip Code)

       Registrant's telephone number, including area code: (712) 277-1340

Securities registered pursuant to Section 12(b) of the Act:

                                                           Name of each
        Title of each class                         exchange on which registered
        -------------------                         ----------------------------
 Common Shares, without par value                     New York Stock Exchange
                                                      Toronto Stock Exchange

Securities registered pursuant to Section 12(g) of the Act:  None

     Indicate by check mark whether the Registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X] No [ ]

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [X]

     The aggregate market value of the Registrant's voting stock held by
non-affiliates of the Registrant, at January 31, 2002, was $111,718,194.

     The number of Common Shares, without par value, outstanding as of March 1,
2002 was 76,472,849.

================================================================================

<PAGE>


     This Amendment No. 1 amends the Registrant's Annual Report on Form 10-K for
the year ended December 31, 2001, and is being filed solely to include a new
exhibit.



                                       1

<PAGE>

                                     PART IV

Item 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K.

(d)  Exhibit

     23.1* Consent of Deloitte & Touche LLP.



                                       2

<PAGE>

                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, as
amended, the Registrant has duly caused this report to be signed on its behalf
by the undersigned, thereunto duly authorized.

                                        TERRA INDUSTRIES INC.

Date:  March 29, 2002                   By:  /s/ FRANCIS G. MEYER
                                             --------------------
                                             Francis G. Meyer
                                             Senior Vice President and
                                             Chief Financial Officer

                                       3