Potash Corporation of Saskatchewan (POT) FWP Free writing prospectus

Filed Pursuant to Rule 433
Registration No. 333-148023

FINAL TERM SHEET

Issuer:	Potash Corporation of Saskatchewan Inc.
Title of Securities:	3.75% Notes due September 30, 2015
Expected Ratings:	Baa1 / A- (Stable/Negative)
Format:	SEC Registered — Registration Statement No. 333-148023
Ranking:	Senior Unsecured
Principal Amount:	$500,000,000
Expected Settlement Date:	September 28, 2009
Trade Date:	September 23, 2009
Maturity Date:	September 30, 2015
Interest Payment Dates:	March 30 and September 30 of each year
First Payment Date:	March 30, 2010
Benchmark Treasury:	2.375% due August 31, 2014
Benchmark Treasury Price:	99–20+
Benchmark Treasury Yield:	2.453%
Spread to Benchmark Treasury:	T + 140 basis points
Reoffer Yield:	3.853%
Coupon:	3.75% payable semi-annually
Price to Public:	99.452%
Day Count:	30/360
Minimum Denominations:	$2,000 x $1,000
Redemption Make Whole:	At any time at the adjusted treasury rate plus 25 basis points
CUSIP Number / ISIN Number:	73755LAG2 / US73755LAG23
Joint Book-Running Managers:	Banc of America Securities LLC
	HSBC Securities (USA) Inc.
	RBC Capital Markets Corporation
Co-Managers:	Scotia Capital (USA) Inc.
	BMO Capital Markets Corp.
	CIBC World Markets Corp.
	Rabo Securities USA, Inc.
	TD Securities (USA) LLC
	UBS Securities LLC
	Mitsubishi UFJ Securities (USA), Inc.
	SG Americas Securities, LLC
	Comerica Securities, Inc.
	Goldman, Sachs & Co.
	Morgan Stanley & Co. Incorporated

Issuer:	Potash Corporation of Saskatchewan Inc.
Title of Securities:	4.875% Notes due March 30, 2020
Expected Ratings:	Baa1 / A- (Stable/Negative)
Format:	SEC Registered — Registration Statement No. 333-148023
Ranking:	Senior Unsecured
Principal Amount:	$500,000,000
Expected Settlement Date:	September 28, 2009
Trade Date:	September 23, 2009
Maturity Date:	March 30, 2020
Interest Payment Dates:	March 30 and September 30 of each year
First Payment Date:	March 30, 2010
Benchmark Treasury:	3.625% due August 15, 2019
Benchmark Treasury Price:	101–05
Benchmark Treasury Yield:	3.485%
Spread to Benchmark Treasury:	T + 150 basis points
Reoffer Yield:	4.985%
Coupon:	4.875% payable semi-annually
Price to Public:	99.109%
Day Count:	30/360
Minimum Denominations:	$2,000 x $1,000
Redemption Make Whole:	At any time at the adjusted treasury rate plus 25 basis points
CUSIP Number / ISIN Number:	73755LAH0 / US73755LAH06
Joint Book-Running Managers:	Banc of America Securities LLC
	HSBC Securities (USA) Inc.
	RBC Capital Markets Corporation
Co-Managers:	Scotia Capital (USA) Inc.
	BMO Capital Markets Corp.
	CIBC World Markets Corp.
	Rabo Securities USA, Inc.
	TD Securities (USA) LLC
	UBS Securities LLC
	Mitsubishi UFJ Securities (USA), Inc.
	SG Americas Securities, LLC
	Comerica Securities, Inc.
	Goldman, Sachs & Co.
	Morgan Stanley & Co. Incorporated

A securities rating is not a recommendation to buy, sell or hold securities and may be subject to revision or withdrawal at any time.

The Issuer has filed a Registration Statement on Form S-3 (including a base prospectus dated December 12, 2007, as supplemented by a preliminary prospectus supplement, dated September 23, 2009, the “Prospectus”) with the SEC for the offering to which this communication relates. Before you invest, you should read the Prospectus and the documents incorporated therein by reference that the Issuer has filed with the SEC for more complete information about the Issuer and this offering. You may obtain these documents for free by visiting EDGAR on the SEC website at www.sec.gov. Alternatively, the Issuer, any underwriter or any dealer participating in the offering will arrange to

send you the Prospectus and any document incorporated by reference in the Prospectus if you request it by calling toll-free 1-800-294-1322 or you may e-mail a request to dg.prospectus_distribution@bofasecurities.com, HSBC Securities (USA) Inc. toll-free at 1-866-811-8049 or RBC Capital Markets Corporation toll-free at 1-866-375-6829.

Any legends, disclaimers or other notices that may appear below are not applicable to this communication and should be disregarded. Such legends, disclaimers or other notices have been automatically generated as a result of this communication having been sent via Bloomberg or another system.