<Page>

                                                                EXHIBIT 4.ii.(c)

                             SUPPLEMENTAL INDENTURE

          This Supplemental Indenture (this "Supplemental Indenture"), dated as
of July 1, 2002, by and among IMC Sulphur Holdings LLC (the "Guaranteeing
Subsidiary"), a subsidiary of IMC Global Inc., a Delaware corporation (the
"Company"), the Company and The Bank of New York, as trustee under the Indenture
referred to below (the "Trustee").

                                W I T N E S E T H

          WHEREAS, the Company has heretofore executed and delivered to the
Trustee an indenture (the "Seven Year Indenture"), dated as of May 17, 2001
providing for the issuance of an aggregate principal amount of up to $400
million of 10.875% Senior Notes due 2008 (the "Seven Year Notes");

          WHEREAS, the Company has heretofore executed and delivered to the
Trustee an indenture (the "Ten Year Indenture" and together with the Seven Year
Indenture, the "Indenture"), dated as of May 17, 2001 providing for the issuance
of an aggregate principal amount of up to $300 million of 11.250% Senior Notes
due 2011 (the "Ten Year Notes" and together with the Seven Year Notes, the
"Notes");

          WHEREAS, Section 10.04 of the Indenture provides that, if a Person
becomes obligated to guarantee the Notes pursuant to the Indenture, the new
guarantor must execute a supplemental indenture to which such Guarantor shall
unconditionally guarantee all of the Company's obligations under the Notes and
the Indenture on the terms and conditions set forth herein and in the Indenture;
and

          WHEREAS, pursuant to Section 8.06 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

          NOW THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt of which is hereby acknowledged, the
parties hereto mutually covenant and agree for the equal and ratable benefit of
the Holders of the Notes as follows:

          1.   CAPITALIZED TERMS. Capitalized terms used herein without
definition shall have the meanings assigned to them in the Indenture.

          2.   AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby agrees
to become subject to the terms of the Indenture as a Guarantor.

          3.   INCORPORATION OF TERMS OF INDENTURE. The obligations of the
Guaranteeing Subsidiary under the Note Guarantees shall be governed in all
respects by the terms of the Indenture and shall constitute a Note Guarantee
thereunder. The Guaranteeing Subsidiary shall be bound by the terms of the
Indenture as they relate to the Note Guarantees.

          4.   NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any obligations of the Company
or the Guaranteeing Subsidiary under the Notes, any Note Guarantees, the
Indenture or this Supplemental Indenture or for any claim based on, in


IMC Sulphur Holdings LLC Supplemental Indenture

<Page>

respect of, or by reason of, such obligations or their creation. Each Holder of
the Notes by accepting a Note waives and releases all such liability. The waiver
and release are part of the consideration for issuance of the Notes. Such waiver
may not be effective to waive liabilities under the federal securities laws and
it is the view of the SEC that such a waiver is against public policy.

          5.   NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK
SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

          6.   COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

          7.   EFFECT OF HEADINGS. The Section headings herein are for
convenience only and shall not affect the construction hereof.

          8.   TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Company.

<Page>

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed and attested, all as of the date first above
written.

Dated: July 10, 2002


                                      IMC GLOBAL INC.

                                      By: /s/ E. Paul Dunn, Jr.
                                          --------------------------------------
                                          Name:  E. Paul Dunn, Jr.
                                          Title: Vice President, Finance and
                                                 Treasurer


                                      IMC SULPHUR HOLDINGS LLC

                                      By: /s/ E. Paul Dunn, Jr.
                                          --------------------------------------
                                          Name:  E. Paul Dunn, Jr.
                                          Title: Treasurer


                                      THE BANK OF NEW YORK, as Trustee

                                      By: /s/ Robert D. Foltz
                                          --------------------------------------
                                          Name:  ROBERT D. FOLTZ
                                          Title: AGENT


IMC Sulphur Holdings LLC Supplemental Indenture