Exhibit 8.1

January 12, 2016

CVR Partners, LP

2277 Plaza Drive, Suite 500

Sugar Land, Texas 77479

Ladies and Gentlemen:

We have acted as counsel to CVR Partners, LP, a Delaware limited partnership (“CVR”), in connection with the filing of a registration statement on Form S-4 (the “Registration Statement”), filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Securities Act”), relating to the transactions (the “Mergers”) contemplated by the Agreement and Plan of Merger (the “Merger Agreement”) dated as of August 9, 2015, by and among CVR, Lux Merger Sub 1, LLC, a Delaware limited liability company, Lux Merger Sub 2, LLC, a Delaware limited liability company, Rentech Nitrogen Partners, L.P., a Delaware limited partnership, and Rentech Nitrogen GP, LLC, a Delaware limited liability company.

This opinion is based on various facts and assumptions, including the facts and assumptions disclosed in the Registration Statement, and the consummation of the Mergers in the manner contemplated by, and in accordance with, the terms set forth in the Merger Agreement and the Registration Statement, and is conditioned upon representations made by CVR and Rentech Nitrogen Partners, L.P. confirming the accuracy of such facts and assumptions through a certificate of an officer delivered to us for the purposes of this opinion (the “Officer’s Certificates”).

In our capacity as counsel to CVR, we have made such legal and factual examinations and inquiries, including an examination of originals or copies certified or otherwise identified to our satisfaction of such documents, corporate records and other instruments, as we have deemed necessary or appropriate for purposes of this opinion. In our examination, we have assumed the authenticity of all documents submitted to us as originals, the genuineness of all signatures thereon, the legal capacity of natural persons executing such documents and the conformity to authentic original documents of all documents submitted to us as copies. For the purpose of our opinion, we have not made an independent investigation or audit of the facts set forth in the above-referenced documents or in the Officer’s Certificates. In addition, in rendering this opinion we have assumed the truth and accuracy of all representations and statements made to us which are qualified as to knowledge or belief, without regard to such qualification.

We hereby confirm that all statements of legal conclusions contained in the discussion in the Registration Statement under the caption “Material U.S. Federal Income Tax Consequences of CVR Partners Common Unit Ownership” constitute the opinion of Vinson & Elkins L.L.P. with respect to the matters set forth therein as of the effective date of the Registration Statement, subject to the assumptions, qualifications, and limitations set forth therein.

No opinion is expressed as to any matter not discussed in the Registration Statement under the caption “Material U.S. Federal Income Tax Consequences of CVR Partners Common Unit Ownership.” We are opining herein only as to the federal income tax matters described above, and we express no opinion with respect to the applicability to, or the effect on, any transaction of other federal laws, foreign laws, the laws of any state or any other jurisdiction or as to any matters of municipal law or the laws of any other local agencies within any state.

This opinion is rendered to you as of the effective date of the Registration Statement, and we undertake no obligation to update this opinion subsequent to the date hereof. This opinion is furnished to you, and is for

Vinson & Elkins LLP  Attorneys at Law Abu Dhabi  Austin  Beijing  Dallas  Dubai  Hong Kong  Houston  London   Moscow New York  Palo Alto  Riyadh  San Francisco  Tokyo  Washington 1001 Fannin Street, Suite 2500 Houston, TX 77002-6760 Tel +1.713.758.2222  Fax +1.713.758.2346  www.velaw.com

January 12, 2016     Page 2

your use in connection with the transactions set forth in the Registration Statement. In addition, this opinion may be relied on by persons entitled to rely on it pursuant to applicable provisions of federal securities law. However, this opinion may not be relied upon for any other purpose or furnished to, assigned to, quoted to or relied upon by any other person, firm or other entity, for any purpose, without our prior written consent.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement. By giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act and the rules and regulations thereunder.

Very truly yours,

/s/ VINSON & ELKINS L.L.P.

Vinson & Elkins L.L.P.