Exhibit 4(a)

THIS SECURITY IS IN GLOBAL FORM WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), OR A NOMINEE OF DTC, WHICH MAY BE TREATED BY THE COMPANY, THE TRUSTEE AND ANY AGENT THEREOF AS OWNER AND HOLDER OF THIS SECURITY FOR ALL PURPOSES.

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF DTC TO POTASH CORPORATION OF SASKATCHEWAN INC. (“THE COMPANY”) OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR SECURITIES IN DEFINITIVE FORM IN THE LIMITED CIRCUMSTANCES REFERRED TO IN THE INDENTURE, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY DTC TO A NOMINEE OF DTC OR BY A NOMINEE OF DTC TO DTC OR ANOTHER NOMINEE OF DTC OR BY DTC OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY.

POTASH CORPORATION OF SASKATCHEWAN INC.

4.000% Notes due December 15, 2026

POTASH CORPORATION OF SASKATCHEWAN INC., a Canadian corporation (hereinafter called the “Company,” which term shall include any successor entity under the Indenture), for value received, hereby promises to pay to Cede & Co., as nominee for DTC, or registered assigns, upon presentation, the principal sum of                     DOLLARS ($            ) on December 15, 2026 and to pay interest thereon from June 15, 2017 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on June 15 and December 15 in each year, commencing June 15, 2017, at the rate of 4.000% per annum, until the entire principal amount hereof is paid or made available for payment.

The interest so payable, and punctually paid or duly provided for on any Interest Payment Date will, as provided in the Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be June 1 or December 1 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for shall forthwith cease to be payable to the Holder on such Regular Record Date, and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not more than 15 days and not less than 10 days prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities may be listed, and upon such notice as may be required by such exchange, all as more fully provided in the Indenture.

Payment of the principal of, interest on and Additional Amounts, if any, with respect to this global Security will be paid to DTC for the purpose of permitting DTC to credit the principal and interest received by it in respect of this global Security to the accounts of the beneficial owners thereof; provided, however, that if this Security is not a global Security, payment of the principal of, interest on and Additional Amounts, if any, with respect to this Security will be made at the office or agency of the Trustee in The City of New York, or elsewhere as provided in the Indenture, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; and provided, further, that at the option of the Company payment of interest may be made by (a) check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register or (b) transfer to an account of the Person entitled thereto located inside the United States.

Additional provisions of this Security are set forth following the signature page hereof, which provisions shall for all purposes have the same effect as if set forth at this place.

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IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed this          day of         ,         .

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TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This is one or all of the Securities of the series designated “4.000% Notes due December 15, 2026” pursuant to the within-mentioned Indenture.

Dated:

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POTASH CORPORATION OF SASKATCHEWAN INC.

4.000% Notes due December 15, 2026

This Security is one or all of a duly authorized issue of securities of the Company (herein called the “Securities”) issued and to be issued in one or more series under an Indenture, dated as of February 27, 2003 (herein called the “Indenture”), between the Company and U.S. Bank National Association (as successor trustee to The Bank of Nova Scotia Trust Company of New York), as trustee (herein called the “Trustee”, which term includes any successor trustee under the Indenture), to which Indenture and all indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitation of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one or all of the series designated as the “4.000% Notes due December 15, 2026.”

At any time prior to the Par Call Date (as defined below), the Securities in this series are redeemable, in whole or in part, at the Company’s option at any time and from time to time at a Redemption Price equal to the greater of (i) 100% of the principal amount of the Securities to be redeemed and (ii) the sum of the present values of the Remaining Scheduled Payments (as defined below) discounted to the relevant Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Adjusted Treasury Rate (as defined below) plus 25 basis points, together with, in each case, accrued and unpaid interest on the principal amount of the Securities to be redeemed to the Redemption Date.

At any time on or after the Par Call Date, the Securities in this series will be redeemable in whole or in part, at the Company’s option at any time and from time to time at a Redemption Price equal to 100% of the principal amount of the Securities to be redeemed plus accrued and unpaid interest on the principal amount of the Securities to be redeemed to the Redemption Date.

Notwithstanding the foregoing, installments of interest on Securities that are due and payable on Interest Payment Dates falling on or prior to a Redemption Date will be payable on the Interest Payment Date to the registered Holders as of the close of business on the Regular Record Date according to the Securities and the Indenture.

In connection with such optional redemption, the following defined terms apply:

“Adjusted Treasury Rate” means, with respect to any Redemption Date, the rate per annum equal to the semi-annual equivalent yield to maturity (computed as of the third Business Day immediately preceding that Redemption Date) or interpolated (on a day count basis) of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for that Redemption Date.

“Comparable Treasury Issue” means the United States Treasury security or securities selected by the Independent Investment Banker that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt

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securities of comparable maturity to the remaining term of the Securities to be redeemed (assuming, for this purpose, that the Securities matured on the Par Call Date).

“Comparable Treasury Price” means, with respect to any Redemption Date, (a) the average of the Reference Treasury Dealer Quotations for that Redemption Date, after excluding the highest and lowest of such Reference Treasury Dealer Quotations, or (b) if the Independent Investment Banker for the Securities obtains fewer than five such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means one of the Reference Treasury Dealers appointed by the Company to act as the “Independent Investment Banker.”

“Par Call Date” means September 15, 2026.

“Reference Treasury Dealer” means (a) Goldman, Sachs & Co., Morgan Stanley & Co. LLC, RBC Capital Markets, LLC or Scotia Capital (USA) Inc. and their respective affiliates or successors and one other nationally recognized investment banking firm that is a primary U.S. Government securities dealer in New York City (a “Primary Treasury Dealer”) specified from time to time by the Company; provided, however, that if any of the foregoing shall cease to be a Primary Treasury Dealer, the Company shall substitute therefor another nationally recognized investment banking firm that is a Primary Treasury Dealer or (b) any other Primary Treasury Dealer selected by the Company.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Independent Investment Banker, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Independent Investment Banker by such Reference Treasury Dealer at 3:30 p.m., New York City time, on the third Business Day preceding that Redemption Date.

“Remaining Scheduled Payments” means, with respect to each Security to be redeemed, the remaining scheduled payments of the principal thereof and interest thereon that would be due if such Securities matured on the Par Call Date but for such redemption; provided, however, that, if that Redemption Date is not an Interest Payment Date with respect to such Security, the amount of the next succeeding scheduled interest payment thereon will be reduced by the amount of interest accrued thereon to that Redemption Date.

Notice of any redemption will be mailed at least 30 days but not more than 60 days before the Redemption Date to each Holder of the Securities in this series to be redeemed. On and after any Redemption Date, interest will cease to accrue on the Securities in this series or any portion thereof called for redemption. On or before any Redemption Date, the Company shall deposit with the Trustee or with a Paying Agent money sufficient to pay the Redemption Price of and accrued interest on the Securities in this series to be redeemed on such date. If less than all the Securities in this series are to be redeemed, the Securities to be redeemed shall be selected by the Trustee at the Company’s direction by such method as the Company and the Trustee shall deem fair and appropriate. The Redemption Price shall be calculated by the Independent

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Investment Banker, and the Company, the Trustee and any Paying Agent for the Securities of this series shall be entitled to rely on such calculation.

The Securities in this series are redeemable, at the Company’s option, at any time as a whole but not in part, upon not less than 30 nor more than 60 days prior written notice to the Holders (with a copy to the Trustee, Paying Agent and Transfer Agent), at a Redemption Price equal to 100% of the aggregate principal amount of the Securities, plus any Additional Amounts and accrued and unpaid interest to the Redemption Date (subject to the right of Holders of record on a Regular Record Date to receive interest due on the respective Interest Payment Date), in the event there is a substantial probability that the Company has become or would become obligated to pay, on the next date on which any amount would be payable with respect to the Securities, any Additional Amounts as a result of (i) an amendment of or change in the laws (including any regulations promulgated thereunder) of Canada or of any province or territory of Canada or by any authority or agency therein or thereof having the power to tax; or (ii) any change in or amendment to any official position or the introduction of an official position of a taxing authority, legislative body, court, governmental agency or regulatory authority in Canada or of any province or territory of Canada or by any authority or agency therein or thereof having the power to tax, regarding the application or interpretation of such laws or regulations (each of (i) and (ii) a “Change in Tax Law”), which change or amendment is publicly announced or becomes effective on or after December 1, 2016 (or the date a party organized in a jurisdiction other than Canada becomes our successor).

The notice of redemption referred to in the proceeding paragraph may not be given earlier than 90 days prior to the earliest date on which the Company would be obligated to pay such Additional Amounts were a payment in respect of the Securities then due and payable. Any such redemption shall be consummated upon not less than 30 days nor more than 60 days’ prior written notice.

Before the Company publishes or mails notice of redemption of the Securities as described in the two previous paragraphs, the Company will deliver to the Trustee an Officers’ Certificate to the effect that the Company is entitled to redeem the Securities pursuant to the terms of the Indenture and such notice shall not be effective until the Company delivers to the Trustee an Opinion of Counsel to the effect that there is a substantial probability that Additional Amounts will be payable on the next payment date in respect of the Securities as a result of a Change in Tax Law. The Company will, prior to or contemporaneously with the publication or mailing of any notice of redemption of any Securities as described in this paragraph and the two previous paragraphs, furnish to the Trustee, Paying Agent and Transfer Agent a copy of such notice of redemption.

If a Change of Control Triggering Event occurs with respect to the Securities, unless the Company has exercised its right to redeem the Securities as described above, it will be required to make an offer to repurchase all, or any part (equal to $2,000 or an integral multiple of $1,000 in excess thereof), of each Holder’s Securities pursuant to the offer described below (the “Change of Control Offer”) on the terms set forth herein. In the Change of Control Offer, the Company will be required to offer payment in cash equal to 101% of the aggregate principal amount of Securities repurchased plus accrued and unpaid interest, if any, on the Securities repurchased, to the date of purchase (the “Change of Control Payment”).

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Within 30 days following any Change of Control Triggering Event, the Company will be required to mail a notice to Holders of Securities describing the transaction or transactions that constitute the Change of Control Triggering Event and offering to repurchase the Securities on the date specified in the notice, which date will be no earlier than 30 days and no later than 60 days from the date such notice is mailed (the “Change of Control Payment Date”), pursuant to the procedures required herein and described in such notice. The Company must comply with the requirements of Rule 14e-1 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and any other securities laws and regulations thereunder to the extent those laws and regulations are applicable in connection with the repurchase of the Securities as a result of a Change of Control Triggering Event. To the extent that the provisions of any applicable securities laws or regulations conflict with the Change of Control provisions herein, the Company will be required to comply with the applicable securities laws and regulations and will not be deemed to have breached its obligations under the Change of Control provisions herein by virtue of such conflicts.

On the Change of Control Payment Date, the Company will be required, to the extent lawful, to:

(a) accept for payment all Securities or portions of Securities properly tendered pursuant to the Change of Control Offer;

(b) deposit with the Paying Agent an amount equal to the Change of Control Payment in respect of all Securities or portions of Securities properly tendered; and

(c) deliver or cause to be delivered to the Trustee the Securities properly accepted together with an Officers’ Certificate stating the aggregate principal amount of Securities or portions of Securities being purchased by the Company.

The Paying Agent will be required to mail promptly to each Holder who properly tendered Securities the purchase price for such Securities and the Trustee will be required to authenticate and mail (or cause to be transferred by book entry) promptly to each such Holder a new Security equal in principal amount to any unpurchased portion of the Securities surrendered, if any; provided that each new Security will be in a principal amount of $2,000 or an integral multiple of $1,000 in excess thereof.

For purposes of the foregoing discussion of a repurchase at the option of Holders, the following definitions are applicable:

“Below Investment Grade Rating Event” means the rating on the Securities is changed from an Investment Grade Rating to below an Investment Grade Rating by each of the Rating Agencies (as defined below) on any date from the date of the public notice of an arrangement that could result in a Change of Control until the end of the 60-day period following public notice of the occurrence of the Change of Control (which 60-day period shall be extended so long as the rating of the Securities is under publicly announced consideration for possible downgrade by any of the Rating Agencies).

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“Change of Control” means the occurrence of any of the following: (1) the direct or indirect sale, transfer, conveyance or other disposition (other than by way of merger, amalgamation, arrangement or consolidation), in one or a series of related transactions, of all or substantially all of the Company’s properties or assets and those of its subsidiaries taken as a whole to any Person other than the Company or one of its subsidiaries; (2) the consummation of any transaction (including, without limitation, any merger, amalgamation, arrangement or consolidation) the result of which is that any Person becomes the beneficial owner, directly or indirectly, of more than 50% of the total voting power in the aggregate of all classes of the Company’s voting stock normally entitled to vote in elections of directors; or (3) the first day on which a majority of the members of the Company’s Board of Directors are not Continuing Directors. Notwithstanding the foregoing, the combination of the Company’s business with Agrium Inc. (“Agrium”) in a merger of equals transaction by way of a plan of arrangement under Section 192 of the Canada Business Corporation Act, pursuant to that certain arrangement agreement between the Company and Agrium, dated September 11, 2016, as the same may be amended, restated, modified, or supplemented from time to time, shall not constitute a Change of Control with respect to the Securities for purposes of the Indenture.

“Change of Control Triggering Event” means the occurrence of both a Change of Control and a Below Investment Grade Rating Event.

“Continuing Directors” means, as of any date of determination, any member of the Company’s Board of Directors who (1) was a member of such Board of Directors on December 1, 2016; or (2) was nominated for election or elected to such Board of Directors with the approval of a majority of the Continuing Directors who were members of such Board of Directors at the time of such nomination or election (either by a specific vote or by approval of the Company’s proxy statement in which such member was named as a nominee for election as a director, without objection to such nomination).

“Investment Grade Rating” means a rating equal to or higher than Baa3 (or the equivalent) by Moody’s and BBB- (or the equivalent) by S&P or the equivalent investment grade rating from any additional Rating Agency or Rating Agencies.

“Moody’s” means Moody’s Investors Service, Inc.

“Person” means any individual, partnership, corporation, limited liability company, joint stock company, business trust, trust, unincorporated association, joint venture or other entity, or a government or political subdivision or agency thereof.

“Rating Agencies” means (1) each of Moody’s and S&P; and (2) if either Moody’s or S&P ceases to rate the Securities or fails to make a rating of the Securities publicly available for reasons outside of the Company’s control, a “nationally recognized statistical rating organization” as defined in Section 3(a)(62) of the Exchange Act, selected by the Company (as certified by a resolution of its Board of Directors) as a replacement agency for Moody’s or S&P, or both of them, as the case may be.

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“S&P” means Standard & Poor’s Ratings Services, a division of The McGraw-Hill Companies, Inc.

The failure by the Company to comply with its obligations in the event of a Change of Control Triggering Event described above will constitute an Event of Default with respect to the Securities.

The Indenture contains provisions for defeasance of (a) the entire indebtedness of the Company on this Security and (b) certain restrictive covenants and the related defaults and Events of Default applicable to the Company, in each case, upon compliance by the Company with certain conditions set forth in the Indenture, which provisions apply to this Security. This Security is not subject to repayment at the Holder’s option.

If an Event of Default with respect to the Securities of this series shall occur and be continuing, the principal of the Securities of this series may be declared due and payable in the manner and with the effect provided in the Indenture. Notwithstanding the previous sentence, if an Event of Default occurs as a result of the failure by the Company to comply with its obligations in the event of a Change of Control Triggering Event as described above, the principal of, and any premium and accrued interest on the Securities will become immediately due and payable without any declaration or other act on the part of the Trustee or any Holder of the Securities.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities of this series, the Holders of not less than 25% in principal amount of the Securities of this series at the time Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default and offered the Trustee reasonable indemnity and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities of this series at the time Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any interest on or after the respective due dates expressed herein.

The Indenture permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities under the Indenture at any time by the Company and the Trustee with the consent of the Holders of not less than a majority in principal amount of the Outstanding Securities. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Company with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of

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transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Company in any Place of Payment where the principal of and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar for the Securities duly executed by the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities of this series, of authorized denomination and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities of this series are issuable only in registered form without coupons in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations set forth therein, Securities of this series are exchangeable for a like aggregate principal amount of Securities of this series of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and none of the Company, the Trustee or any such agent shall be affected by notice to the contrary.

The obligations of the Company under the Indenture and this Security and all documents delivered in the name of the Company in connection herewith and therewith do not and shall not constitute personal obligations of the directors, officers, employees, agents or shareholders of the Company or any of them, and shall not involve any claim against or personal liability on the part of any of them, and all persons including the Trustee shall look solely to the assets of the Company for the payment of any claim thereunder or for the performance thereof and shall not seek recourse against such directors, officers, employees, agents or shareholders of the Company or any of them or any of their personal assets for such satisfaction. The performance of the obligations of the Company under the Indenture and this Security and all documents delivered in the name of the Company in connection therewith shall not be deemed a waiver of any rights or powers of the Company or its directors or its shareholders under the Company’s Articles of Continuance.

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All terms used in this Security that are defined in the Indenture shall have the meanings assigned to them in the Indenture.

The Indenture and the Securities, including this Security, shall be governed by and construed in accordance with the law of the State of New York.

Pursuant to a recommendation promulgated by the Committee on Uniform Security Identification Procedures, the Company has caused “CUSIP” numbers to be printed on the Securities as a convenience to the Holders of the Securities. No representation is made as to the correctness or accuracy of such CUSIP numbers as printed on the Securities, and reliance may be placed only on the other identification numbers printed hereon.

Unless the certificate of authentication hereon has been executed by or on behalf of the Trustee by manual signature, this Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

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ASSIGNMENT FORM

FOR VALUE RECEIVED, the undersigned hereby

sells, assigns and transfers unto

PLEASE INSERT SOCIAL

SECURITY OR OTHER IDENTIFYING

NUMBER OF ASSIGNEE

Signature_______________________________________________

NOTICE: The signature to this assignment must correspond with the name as it appears on the first page of the within Security in every particular, without alteration or enlargement or any change whatever.

Signature Guaranteed:______________________________________

NOTICE: Signature(s) must be guaranteed by an “eligible guarantor institution” that is a member or participant in a “signature guarantee program” (e.g., the Securities Transfer Agents Medallion Program, the Stock Exchange Medallion Program and the New York Stock Exchange Medallion Program).

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