<PAGE>   1

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM 10-K

                  FOR ANNUAL AND TRANSITION REPORTS PURSUANT TO
                           SECTIONS 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

          Mark One)
            [x] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934
                     For the fiscal year ended June 30, 1999
                                       OR
          [ ] TRANSITION REPORT PURSUANT TO SECTION 13 or 15(d) OF THE
                         SECURITIES EXCHANGE ACT OF 1934
           For the transition period from ____________ to ____________

                         Commission File Number 0-20411

                        MISSISSIPPI CHEMICAL CORPORATION

-------------------------------------------------------------------------------
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                                                              <C>
                               MISSISSIPPI                                    64-0292638
--------------------------------------------------------------    ----------------------------------
(State or other jurisdiction of incorporation or organization)   (IRS Employer Identification Number)

              Highway 49 East, P.O. Box 388, Yazoo City, MS                     39194
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                (Address of principal executive offices)                     (Zip Code)

          Registrant's telephone number, including area code:              (601) 746-4131
                                                                 ----------------------------------



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

                    Title of each class                             Name of each exchange on which registered
            -----------------------------------------               -----------------------------------------

               Common Stock, par value $.01                                  New York Stock Exchange

              Preferred Stock Purchase Rights                                New York Stock Exchange
</TABLE>

        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. [ ]

At September 14, 1999, Mississippi Chemical Corporation had 26,140,275 shares of
common stock, par value $0.01, outstanding. The Company estimates that the
aggregate market value of the common stock on September 14, 1999 (based upon the
closing price of the common stock on the New York Stock Exchange), held by
nonaffiliates was approximately $206,672,000.
--------------------------------------------------------------------------------
                      DOCUMENTS INCORPORATED BY REFERENCE

Annual Report to Shareholders for fiscal year ended June 30, 1999 (Item 1 in
Part I; Items 5, 6, 7, 7A and 8 in Part II; and Item 14 in Part IV).

Proxy Statement for Annual Meeting of Shareholders to be held on November 9,
1999 (Items 10, 11, 12 and 13 in Part III).


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                                     PART I

ITEM 1.   BUSINESS

        Mississippi Chemical Corporation (the "Company") was incorporated in
Mississippi on May 23, 1994, and is the successor by merger, effective July 1,
1994, to a business which was incorporated in Mississippi in September 1948 as
the first fertilizer cooperative in the United States (the "Cooperative"). The
address of the Company's principal executive office is Owen Cooper
Administration Building, 3622 Highway 49 East, Yazoo City, Mississippi 39194,
and its telephone number is (662) 746-4131. The Company maintains a site on the
World Wide Web at www.misschem.com. The term "Company" includes Mississippi
Chemical Corporation, its subsidiaries and affiliates, Mississippi Phosphates
Corporation; Mississippi Potash, Inc.; Eddy Potash, Inc.; Mississippi Nitrogen,
Inc.; MissChem Nitrogen, L.L.C.; Triad Nitrogen, L.L.C.; TNI Barge, Inc.; MCC
Investments, Inc.; NSI Land Corporation; Mississippi Chemical Management
Company; Mississippi Chemical Company, L.P.; Mississippi Chemical Holdings,
Inc.; MissChem (Barbados) SRL; and MissChem Trinidad Limited. References to the
Company's operations prior to July 1, 1994, refer to the Cooperative's
operations.

        The principal business of the Cooperative was to provide fertilizer
products to its shareholders pursuant to preferred patronage rights that gave
the shareholders the right to purchase fertilizer products and receive a
patronage refund on those purchases. On June 28, 1994, the shareholders of the
Cooperative approved a plan of reorganization (the "Reorganization"), pursuant
to which the Cooperative was merged into the Company. As a result of the
Reorganization, the capital stock of the Cooperative was converted into common
stock and/or cash, and the Company began to operate as a regular business
corporation. Since the Reorganization, the Company has sold the fertilizer
products produced at its facilities to agricultural and industrial customers
around the world. Any reference to an industrial customer or user herein
includes producers who convert products purchased from the Company to another
fertilizer product.

        In December 1994, the Company entered into a 50-50 joint venture with
Farmland Industries, Inc., known as Farmland MissChem Limited ("Farmland
MissChem"), to construct and operate a 2,040-ton-per-day ammonia plant to be
located near Point Lisas, The Republic of Trinidad and Tobago. Construction of
the facility is complete, and the ammonia plant began producing commercial
quantities in July 1998. The Company is obligated by contract to purchase
one-half of the ammonia (approximately 350,000 tons per year) produced by the
plant at a discount to market, subject to a minimum price.

        In August 1996, the Company entered into an agreement to acquire the
fertilizer businesses of First Mississippi Corporation ("First Mississippi") in
an all-stock merger transaction. The transaction was completed on December 24,
1996. The First Mississippi fertilizer operations primarily included a 50%
interest in a facility that included an ammonia plant and a urea plant that at
the time of the acquisition operated under the name Triad Chemical (the Company
already owned the remaining 50% of Triad Chemical) and a stand-alone ammonia
plant. These assets are located on contiguous property in Donaldsonville,
Louisiana.

        In August 1996, the Company, through two subsidiaries of its wholly
owned subsidiary Mississippi Potash, Inc., acquired substantially all of the
assets (including the right to use the corporate names) of New Mexico Potash
Corporation and Eddy Potash, Inc., from Trans-Resources, Inc. Since the
acquisition, New Mexico Potash Corporation has been merged into Mississippi
Potash, Inc. Eddy Potash, Inc., which operated as a wholly owned subsidiary of
Mississippi Potash, Inc., suspended its mining and production operations on
December 3, 1997. The Company is currently evaluating


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alternative methods of mining the Eddy Potash reserves. The original mine and
refinery owned by Mississippi Potash, Inc., is now known as the "West Facility,"
and the former New Mexico Potash Corporation mine is known as the "East
Facility."


                               OPERATING SEGMENTS

        We have three reportable operating segments: nitrogen, phosphates and
potash. The amounts of revenue, operating profit or loss and identifiable assets
attributable to each of our segments is set forth in our 1999 Annual Report to
Shareholders under the caption "Note 12-Segment Information" contained in the
"Notes to Consolidated Financial Statements," which information is incorporated
herein by reference. Additional information about each operating segment is set
forth below.

NITROGEN

  PRODUCTS

        The Company produces nitrogen products at its production facilities in
Yazoo City, Mississippi, and Donaldsonville, Louisiana. The Company's principal
nitrogen products include ammonia; fertilizer-grade ammonium nitrate, which is
sold under the Company's trade name Amtrate(R); UAN solution, which is sold
under the Company's trade name N-Sol(R); urea; and nitric acid. In fiscal 1999,
the Company sold approximately 2.7 million tons of nitrogen products to
fertilizer dealers and distributors and industrial users located primarily in
the southern United States, as compared to approximately 2.5 million tons of
nitrogen products in fiscal 1998. The increase in tons sold in fiscal 1999 is
primarily due to the offtake of ammonia from Farmland MissChem and the ultimate
sale of the ammonia by the Company. Sales of nitrogen products by the Company in
fiscal 1999 were $245.4 million, which represented approximately 52% of net
sales.

        Each of the Company's nitrogen products has its own distinct
characteristics that produce agronomic preferences among end-users. Farmers
determine which nitrogen product to apply based on the crop planted, soil and
weather conditions, regional farming practices, and relative prices for nitrogen
products.

        AMMONIA. The basic nitrogen product is anhydrous ammonia, which is a
necessary raw material for the production of the Company's other nitrogen
products. Anhydrous ammonia, which is 82% nitrogen, is the most concentrated
nitrogen product available. It is synthesized as a gas under high temperature
and pressure. The raw materials used to produce anhydrous ammonia are natural
gas, atmospheric nitrogen, and steam.

        In fiscal 1999, the Company produced approximately 1,558,000 tons of
anhydrous ammonia at its Yazoo City and Donaldsonville facilities and purchased
approximately 275,000 tons pursuant to its contract with Farmland MissChem. In
fiscal 1999, the Company sold approximately 788,000 tons of anhydrous ammonia as
a raw material for industrial users and 31,000 tons as a primary fertilizer for
direct application to crops. The balance of the anhydrous ammonia was consumed
by the Company as a raw material to manufacture its other nitrogen products and
DAP.

        AMMONIUM NITRATE. The Company is the largest manufacturer and marketer
of agricultural-grade ammonium nitrate fertilizer in the United States. Ammonium
nitrate, which is 34% nitrogen, is produced by reacting anhydrous ammonia and
nitric acid. Ammonium nitrate is less subject to volatilization

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(evaporation) losses than other nitrogen products. Due to its stable nature,
ammonium nitrate is the product of choice for such uses as pastures and no-till
row crops where fertilizer is spread upon the surface and is subject to
volatilization losses. The use of conservation tillage, which reduces soil
erosion, is increasing in the United States and should have a positive impact on
ammonium nitrate demand.

        The Company produced approximately 771,000 tons of solid ammonium
nitrate fertilizer at its Yazoo City facility in fiscal 1999. The Company sold
approximately 765,000 tons of solid ammonium nitrate fertilizer and ammonium
nitrate synthesis to fertilizer dealers and distributors in fiscal 1999. The
solid ammonium nitrate produced by the Company is sold under the registered
trade name Amtrate(R).

        UAN SOLUTION. The Company produced approximately 514,000 tons of UAN
solution at its Yazoo City facility in fiscal 1999. The Company sold
approximately 489,000 tons of UAN solution to fertilizer dealers and
distributors in fiscal 1999 under the registered trade name N-Sol(R). N-Sol(R)
is a 32% nitrogen product that is made by mixing urea liquor and ammonium
nitrate liquor. N-Sol(R) is used as a direct application product for cotton,
corn, grains, and pastures, as well as for use in liquid fertilizer blends. Over
the past 20 years, there has been a substantial increase in the use of UAN
solution as a part of the overall growth in the agricultural consumption of
nitrogen products in the United States.

        UREA. In fiscal 1999, the Company produced approximately 544,000 tons of
prilled urea and urea melt at its Donaldsonville facility. The Company sold
approximately 378,000 tons of prilled urea and approximately 178,000 tons of
urea melt in fiscal 1999. Urea is synthesized by the reaction of ammonia and
carbon dioxide. At 46% nitrogen by weight, urea is the most concentrated form of
dry nitrogen. Because urea undergoes a complex series of changes within the soil
before the nitrogen it contains is ultimately converted into a form that can be
used by plants, it is considered a long-lasting form of nitrogen. As a
fertilizer product, urea is acceptable as both a direct-application material and
as an ingredient in fertilizer blends. Approximately 62% of the Company's urea
sales in fiscal 1999 were to industrial users and manufacturers of animal feeds.
The remainder of the urea sales were to fertilizer dealers and distributors.

        NITRIC ACID. In fiscal 1999, the Company sold 54,000 tons of nitric acid
produced at its Yazoo City facility to industrial users and used the balance of
nitric acid produced in fiscal 1999 as a raw material for the production of
Amtrate(R) and N-Sol(R). The Yazoo City facility produces more nitric acid than
any other U.S. facility. Nitric acid is used to produce end products such as
nylon fibers, polyurethane foams, rubber chemicals and specialty fibers.

  PRODUCTION AND PROPERTIES

        YAZOO CITY, MISSISSIPPI. The Yazoo City facility is a closely
integrated, multiplant production complex located on approximately 1,180 acres.
The complex includes two anhydrous ammonia plants, five nitric acid plants, an
ammonium nitrate plant, two urea plants, and a UAN solution plant. One of the
nitric acid plants and the second ammonia plant were added through a recently
completed expansion project. The 650-ton-per-day nitric acid plant became
operational in March 1998, while the 500-ton-per-day ammonia plant became
operational in March 1999. The expansion project at the Yazoo City facility
increased the Company's annual ammonia production capacity to approximately
710,000 tons, annual nitric acid production capacity to approximately 1,055,000
tons, and annual ammonium nitrate capacity to approximately 900,000 tons. The
Company had also planned to make certain modifications to the ammonium nitrate
plant which were expected to add an additional 50,000

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tons of capacity. Those modification plans have been cancelled due to the
current depressed prices for ammonium nitrate. The Company's annual UAN solution
production capacity remains at 550,000 tons.

        The Yazoo City facility includes a 20.5 megawatt cogeneration facility
that produces significant savings by the sequential generation of electricity
and steam. The Yazoo City plant has direct access to barge, rail, and truck
transportation and is strategically located for the purchase of competitively
priced natural gas.

        DONALDSONVILLE, LOUISIANA. The Donaldsonville facility is a closely
integrated, multiplant nitrogen complex located on approximately 740 acres
fronting the Mississippi River at Donaldsonville, Louisiana, which produces
anhydrous ammonia and urea. The facility includes two anhydrous ammonia plants
with a combined annual production capacity of 1,080,000 tons and a urea plant
with an annual production capacity of approximately 560,000 tons.

        The Donaldsonville facility has ready access to rail, truck, and ammonia
pipeline transportation. The plant is also equipped with a deep-water port
facility on the Mississippi River, allowing access to economical oceangoing
vessel and barge transportation for its urea and ammonia products. The facility
is well-positioned for the purchase of competitively priced natural gas.

        TRINIDAD. In fiscal 1999, the Company purchased approximately 275,000
tons of ammonia from the Farmland MissChem facility. This ammonia was used as a
raw material for upgrading into finished fertilizer products at the Company's
existing facilities and to meet the Company's contractual commitments to certain
industrial customers.

  OTHER

        The Company also owns 9 ammonia barges, two UAN barges, and a 50%
interest in an ammonia storage terminal in Pasadena, Texas.

  MARKETING AND DISTRIBUTION

        The Company sells its nitrogen products to fertilizer dealers and
distributors as well as industrial users located primarily in the southern
region of the United States where its facilities are located. Although the
Company has traditionally sold the majority of its nitrogen products through the
agricultural fertilizer distribution chain, an increasing amount of nitrogen
product is being sold to industrial users in order to reduce the Company's
exposure to the seasonal nature of the agricultural fertilizer markets. In
fiscal 1999, approximately 44% of the Company's nitrogen product sales were to
industrial users.

        In the fertilizer distribution chain, distributors operate as
wholesalers supplying dealers who, in turn, sell directly to farmers. Larger
customers (distributors and large multilocation dealers) arrange for
distribution, storage, and financing of nitrogen products. The majority of the
Company's agricultural sales are made to distributors and large dealers in the
Company's primary trade area. The ten states that make up the Company's primary
trade area are Mississippi, Texas, Alabama, Louisiana, Tennessee, Georgia,
Kentucky, Arkansas, Missouri and Florida.

        The Company transports its nitrogen products by barge, rail, pipeline,
truck and oceangoing vessels. The Company's distribution network includes 9
ammonia barges, two UAN barges, numerous trucks, and a pipeline that pumps UAN
solution from its Yazoo City plant to its Yazoo River port facility,

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along with owned or leased warehouses and terminals that are strategically
placed in high-consumption areas. In fiscal 1998, the Company established with
Farmland Industries, Inc., a 50-50 joint venture, FMCL Limited Liability Company
("FMCL"), to arrange for the transportation of ammonia from the Farmland
MissChem facility in Trinidad to the United States and other world markets. FMCL
has executed two long-term time charter agreements for oceangoing vessels with a
European shipowner. Both agreements establish a fixed charter rate for the
vessels during the entire time that the agreements are in effect. The Company
believes that the time charter agreements provide a hedge against unfavorable
fluctuations in shipping rates and will be a cost-effective method of
transporting its Trinidad product.

  RAW MATERIALS

        NATURAL GAS. Natural gas is the primary raw material used by the Company
in the manufacture of nitrogen products. Natural gas is used both as a chemical
feedstock and as a fuel to produce anhydrous ammonia that is then upgraded into
other nitrogen products. During fiscal 1999, the cost of natural gas represented
approximately 73% of the Company's cost of producing ammonia. Because there are
no commercially feasible alternatives for natural gas in the production of
ammonia, the economic success of the Company's nitrogen business depends upon
the availability of competitively priced natural gas.

        In today's natural gas market, the Company's total delivered natural gas
cost generally consists of two components--the market price of the natural gas
in the producing area at the point of delivery into a pipeline and the fee
charged by the pipeline for transporting the natural gas to the Company's
plants. The cost of the transportation component can vary substantially
depending on whether or not the pipeline has to compete for the business.
Therefore, it is extremely important to the Company's competitiveness that it
have access to multiple natural gas sources and transportation services. In
addition to the impact on transmission costs, access alternatives enable the
Company to benefit from natural gas price differences that may exist from time
to time in the various natural gas producing areas.

        The natural gas requirements of the Yazoo City facility are
approximately 72,000 Mcf per day. Since 1996, the Company has received the
majority of its natural gas requirements for the Yazoo City facility from Sonat
Marketing Company ("Sonat"), an affiliate of Southern Natural Gas Company
("Southern"). In order to secure the incremental gas requirements created by the
addition of the new ammonia plant in March 1999, the Company renegotiated its
agreement with Sonat. The new agreement with Sonat, which became effective on
May 15, 1998, allows for the firm delivery of gas, at market-related prices,
through the Yazoo City facility's direct connections to the interstate pipeline
systems operated by Southern and Texas Eastern Transmission Corporation. Pursue
Energy Corporation ("Pursue") continues to be another major natural gas supplier
of the Yazoo City facility from its reserves located in Rankin County,
Mississippi. In addition, the Company's 60-mile, 12-inch-diameter natural gas
pipeline provides the plant with direct access to the Pursue reserves, along
with low-cost transportation of the Pursue gas; direct access to an additional
interstate pipeline; and direct access to a large intrastate gathering and
transmission system in southern Mississippi. As a result of this access to
multiple sources, the Company benefits from competition for the transportation
and supply of natural gas.

        Natural gas requirements for the Donaldsonville facility are
approximately 107,000 Mcf per day. The Donaldsonville facility is located in one
of the primary natural gas producing regions of the United States. The facility
is currently connected to five intrastate pipeline systems and benefits from
intense competition among the many suppliers that have transport capabilities on
the intrastate lines. All of the Donaldsonville facility's current natural gas
requirements are being supplied under fixed-term contracts with Louisiana Gas
Marketing Company, a subsidiary of Enron Corp.; Amoco Energy Trading


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Corporation; Noble Gas Marketing, Inc.; Reliant Energy Services, Inc.; and Coral
Energy Resources, L.P. These contracts provide for market-sensitive pricing and
firm delivery supply commitments.

        As a result of favorable access to natural gas supplies at the Yazoo
City and Donaldsonville facilities, the Company believes that the loss of any
particular supplier would not have a material impact on plant operations at
either location. There have been no significant supply interruptions at either
location.

        Relative to fiscal 1998 levels, the Company's delivered cost of natural
gas decreased approximately 8%. Gas prices can be influenced significantly by
short-term factors such as weather, storage levels, gas transportation
interruptions, and competing fuel prices. The Company uses natural gas futures
contracts to hedge against the risk of market fluctuations in the cost of
natural gas.

        AMMONIA. Ammonia is a necessary raw material for production of the
Company's other nitrogen products. The Company supplied practically all of its
ammonia requirements in fiscal 1999. Third-party ammonia purchases by the
Company from outside suppliers in fiscal 1999 for production of its other
nitrogen products totaled only 2,600 tons. The Company anticipates that it will
be able to supply all of its ammonia requirements in fiscal 2000 as a result of
increased production by the Farmland MissChem facility and the year-round
availability of production from the new ammonia plant at the Yazoo City
facility.

PHOSPHATE

  PRODUCTS

        The Company produces diammonium phosphate fertilizer ("DAP") at its
facility in Pascagoula, Mississippi. In fiscal 1999, the Company produced
approximately 852,000 tons of DAP and sold approximately 788,000 tons.
Approximately 54,000 tons damaged in Hurricane Georges were purchased by one of
the Company's insurers and are not included in the number of tons sold in fiscal
1999. Sales of DAP by the Company in fiscal 1999 were $136.6 million, which
represented approximately 29% of net sales.

        DAP is the most common form of phosphate fertilizer. DAP is produced by
reacting phosphate rock with sulfuric acid to produce phosphoric acid, which is
then combined with ammonia. DAP contains 18% nitrogen and 46% phosphate (P205)
by weight. DAP is an important fertilizer product both for direct application
and for use in blended fertilizers applied to all major types of row crops.

  PRODUCTION AND PROPERTIES

        The Company's phosphate production complex in Pascagoula, Mississippi,
is located on approximately 1,500 acres. The Pascagoula facility is a closely
integrated, multiplant phosphatic fertilizer complex where the primary
facilities are a phosphoric acid plant, two sulfuric acid plants, and a DAP
granulation plant. The plant has storage facilities for finished product (80,000
tons), as well as for the primary raw materials: phosphate rock (100,000 tons),
sulfur (10,000 tons), and ammonia (25,000 tons). All of the phosphate rock used
by the Company is purchased pursuant to a single supply contract with Office
Cherifien des Phosphates ("OCP"), the national phosphate company of Morocco.

        The plant site fronts a deep-water channel that provides direct access
to the Gulf of Mexico. The complex contains docks and off-loading facilities for
receiving shipload quantities of phosphate rock,

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sulfur, and ammonia and for out-loading DAP. The plant's location on deep water
provides the Company with an outbound freight cost advantage over central
Florida DAP producers with respect to international shipments and domestic
shipments along the Mississippi River system.

        Construction of a new phosphogypsum disposal facility at Pascagoula was
substantially completed on June 30, 1998, at an estimated cost of $18 million.
In April 1998, an expansion of the Company's diammonium phosphate manufacturing
facilities at Pascagoula was placed in service. This project increased annual
production capacity from approximately 720,000 to approximately 900,000 tons per
year and increased DAP storage capacity from approximately 40,000 to 80,000
tons.

  MARKETING AND DISTRIBUTION

        Since October 1, 1997, all of the Company's export sales of DAP have
been made through Phosphate Chemicals Export Association, Inc., a Webb-Pomerene
corporation known as PhosChem, and all domestic sales of DAP have been made
through the Company's sales staff. In fiscal 1999, approximately 62% of the DAP
tonnage sold by the Company was sold into international markets through
PhosChem. China and India received approximately 83% and 12%, respectively, of
the DAP tonnage exported by the Company in fiscal 1999. Most domestic sales are
made in barge-lot quantities to major fertilizer distributors and dealers
located on the Mississippi River system. The vast majority of the Company's DAP
is transported by ship and barge, although truck and rail access is also
available.

  RAW MATERIALS

        PHOSPHATE ROCK. Phosphate rock is one of the primary raw materials used
in the manufacture of DAP. The Pascagoula facility's requirements for phosphate
rock are approximately 1.5 million tons per year. On September 15, 1991, the
Company entered into a ten-year contract with OCP to supply all of the phosphate
rock requirements of the Pascagoula facility. The term of this contract has been
extended to June 30, 2016. OCP, the national phosphate company of Morocco, is
the world's largest producer and exporter of phosphate rock and upgraded
phosphates as a company. The contract price for phosphate rock is based on
phosphate rock costs incurred by certain domestic competitors of the Company and
on the operating performance of the Company's phosphate operations. Under this
formula, the Company realizes favorable phosphate rock prices and is afforded
significant protection during periods when market conditions are depressed.
Conversely, in favorable markets, when the Company's DAP operations are
profitable, the contract price of phosphate rock will escalate based on the
profitability of its DAP operations. Pursuant to this contract, the Company and
OCP are required to negotiate further adjustments as needed to maintain the
viability and economic competitiveness of the Pascagoula plant. The strategic
alliance with OCP has functioned effectively since inception, and the Company
considers its relations with OCP to be excellent.

        SULFUR. Sulfur is used in the manufacture of sulfuric acid at the
Pascagoula plant. Sulfur is in adequate supply and is available on the open
market in quantities sufficient to satisfy the Company's current requirements,
which are approximately 330,000 tons per year. The location of the Company's
plant at Pascagoula, Mississippi, near major oil and gas fields that supply
substantial amounts of sulfur, provides the Company with a strategic advantage
in the purchase of sulfur over its Florida competitors.

        AMMONIA. Ammonia is a necessary raw material for production of DAP.
Third-party ammonia purchases by the Company from outside suppliers in fiscal
1999 for use as a raw material in the production of DAP were only 32,000 tons.
The Company anticipates that it will be able to supply all of its ammonia
requirements in fiscal 2000 as a result of increased production by the Farmland
MissChem

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facility and the year-round availability of production from the new ammonia
plant at the Yazoo City facility.

POTASH

  PRODUCTS

        The Company produces potash at two mines and related facilities near
Carlsbad, New Mexico, which are referred to by the Company as the "East
Facility" and the "West Facility." The Company also operates a granular
compaction plant near the East and West Facilities which is referred to as the
"North Facility." In fiscal 1999, the Company produced approximately 944,000
tons of potash and sold approximately 921,000 tons, primarily in granular form.
Sales of potash products by the Company in fiscal 1999 were $85.9 million, which
represented approximately 18% of net sales.

        The Company's potash is mined from subterranean salt deposits containing
a mixture of potassium chloride and sodium chloride. The Carlsbad, New Mexico,
potash deposits are located from 800 to 1,200 feet below the surface. Potash is
produced in a refining process by which the potassium chloride is separated from
the sodium chloride.

        Potash is an important fertilizer product for both direct application
and for use in blended fertilizers applied to all types of crops. In addition,
certain forms of potash can be used as a raw material in the production of
industrial products such as potassium hydroxide and potassium nitrate.

  PRODUCTION AND PROPERTIES

        The West Facility, which consists of a potash mine and refinery, has an
annual production capacity of 545,000 tons of red potash as a result of a
100,000-ton expansion that was completed in the third quarter of fiscal 1999.
All of the refined product produced at the West Facility is transported to the
North Facility compaction plant for conversion to granular form and is sold to
agricultural fertilizer dealers and distributors. Located contiguous to the
North Facility are storage and shipping facilities from which the finished
product is transported by rail and truck to agricultural customers in both the
domestic and export markets.

        The East Facility, which has an annual production capacity of 550,000
tons of white potash, consists of a potash mine, refinery, and compaction plant.
All of the refined product produced at the East Facility is a higher-purity
potash in standard form. Approximately 40% of that production is converted to a
granular form at the on-site compaction plant and sold as an agricultural
fertilizer. The remaining 60% is sold to agricultural and industrial users in
its original standard form. The East Facility also has storage and shipping
facilities suitable for the distribution of product by rail and truck to the
Company's agricultural and industrial customers.

        On December 3, 1997, the Company suspended the plant operations of Eddy
Potash due to the fact that the depletion of the higher-grade ore zone rendered
the continued operation of conventional mining methods at Eddy Potash
uneconomical. The Company continues to evaluate alternative mining methods for
the Eddy Potash reserves.

        The Company's potash reserves are controlled under long-term federal and
state potassium leases on approximately 182,000 acres. The estimates of potash
ore reserves are calculated using the latest bore hole data and sophisticated
modeling programs. According to the latest model completed in

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September 1999, the Company's total reserves are estimated to be 522 million
tons with an average grade of 15.2% K2O. The recoverable reserves are estimated
to be 467 million tons at an average grade of 14.5% K2O. This reserve base is
estimated to be equivalent to approximately 90 million tons of muriate of
potash. Eddy Potash's reserves are excluded since these estimates include only
the reserves which can be economically recovered by conventional mining
techniques. At current production rates, the Company's combined reserves at the
East and West Facilities have a remaining life of several decades.

  MARKETING AND DISTRIBUTION

        The majority of the Company's agricultural potash sales are in domestic
markets in the states west of the Mississippi River where it enjoys freight cost
advantages over Canadian and overseas potash producers. In order to increase
profit margins, domestic sales are targeted for locations along the freight
route of the Burlington Northern Santa Fe Railroad. Domestic potash marketing is
coordinated from a sales office located in Dallas, Texas. Approximately 21% of
the fiscal 1999 potash sales were to industrial customers, with the remainder of
sales to agricultural customers. Approximately 19% of the Company's fiscal 1999
potash sales were to international markets. The Company's export sales are made
through Potash Corporation of Saskatchewan Sales Limited. The fiscal 1999 export
sales were to Mexico, Central and South America, and Japan. Potash for export is
transported by rail to Mexico and to terminal facilities on the Texas Gulf
Coast, where it is loaded onto oceangoing vessels for shipment.

COMPETITION

        Since fertilizers are global commodities available from numerous
sources, fertilizer suppliers compete primarily on the basis of delivered price.
Other competitive factors include product quality, customer service, and
availability of product. In each product category, the Company competes with a
broad range of domestic producers, including farmer cooperatives, subsidiaries
of larger companies, integrated energy companies, and independent fertilizer
companies. Many of the Company's domestic competitors have larger financial
resources and sales than the Company. The Company also competes with foreign
producers. Foreign competitors often have access to cheaper raw materials or are
owned or subsidized by their governments and, as a result, may have cost
advantages over domestic companies. Additionally, foreign competitors are
frequently motivated by nonmarket factors such as the need for hard currency.

        The Company produces and sells its nitrogen products primarily in the
southern United States where it enjoys a logistical and freight advantage over
foreign competitors and certain domestic competitors. However, dealers and
distributors located in this region re-market a substantial quantity of these
nitrogen products to end users outside of the southern United States. Because
competition is based largely on the delivered price, maintaining low production
costs is critical to competitiveness. Natural gas comprises a significant
portion of the raw materials cost of the Company's nitrogen products.
Competitive natural gas purchasing is essential to maintaining the Company's
low-cost position. This is especially true considering that certain foreign
competitors can purchase natural gas at a lower price than the price typically
paid by the Company. Equally important is efficient use of this gas because of
the energy-intensive nature of the nitrogen business. Therefore,
cost-competitive production facilities that allow flexible upgrading of ammonia
to other finished products are critical to a low-cost competitive position. In
the highly fragmented nitrogen market, product quality and customer service also
can be sources of product differentiation.

        The Company customarily sells approximately two-thirds of its DAP in
international markets. The U.S. phosphate industry has become more concentrated
as a result of recent consolidations and joint

                                       10
<PAGE>   11

ventures, and the Company is smaller than most of its competitors in terms of
resources and sales. Most of the Company's principal competitors have captive
sources of some or all of the raw materials, and this may provide them with cost
advantages. The Company's long-term phosphate rock contract with its flexible
pricing mechanism is a key element to the Company's ability to compete.

        Most potash consumed in the United States is provided by large Canadian
producers who have economies of scale and lower variable costs than their U.S.
counterparts. Over 80% of U.S. potash production capacity is located in the
Carlsbad, New Mexico, area. While the Carlsbad producers have higher mining
costs than the Canadian producers, this disadvantage may be offset by logistical
and freight advantages in certain markets in the southwestern United States and
the lower United States Corn Belt.

RESEARCH AND DEVELOPMENT

        The Company has a research and development staff of 13 full-time
professional employees whose activities relate primarily to the improvement of
the Company's products and development of new applications for the Company's
products. Expenditures on research activities sponsored by the Company were
approximately $1.2 million in fiscal 1999; $1.6 million in fiscal 1998, and $1.3
million in fiscal 1997.

EMPLOYEES

        As of June 30, 1999, the Company employed approximately 1,550 persons
throughout all of its locations, none of which are represented by unions. The
Company considers its employee relations to be satisfactory.

COMPLIANCE WITH ENVIRONMENTAL REGULATIONS

        The Company's operations are subject to federal, state, and local laws
and regulations pertaining to the environment, among which are the Clean Air
Act, the Clean Water Act, the Resource Conservation and Recovery Act, the
Comprehensive Environmental Response, Compensation and Liability Act, the Toxic
Substances Control Act, and various other federal and state statutes. The
Company's facilities require operating permits that are subject to review by
governmental agencies.

        Capital expenditures related to environmental obligations for the past
three fiscal years were approximately as follows: 1999 - $1.96 million; 1998 -
$8.8 million; 1997 - $8.4 million. Environmental capital expenditures are
expected to be approximately $2.4 million for fiscal 2000.

        The Company has accrued costs for the future closure of the west gypsum
disposal facility located at Pascagoula, Mississippi. The balance of the accrual
as of June 30, 1999, is $8.8 million. The Company is currently working with
regulatory officials to develop an engineering plan for closure of the west
facility. The conclusions reached in this engineering plan will determine
whether the Company has to accrue additional costs relating to the closure of
the west facility.

        The Company believes that its policies and procedures now in effect are
in compliance with applicable laws and with the permits relating to the
facilities in all material respects. However, in the normal course of its
business, the Company is exposed to risks relating to possible releases of
hazardous substances into the environment. Such releases could cause substantial
damage or injuries.

                                       11
<PAGE>   12

Environmental expenditures have been and will continue to be material. It is
impossible to predict or quantify the impact of future environmental laws,
regulations and costs.

SEASONALITY

        Sales of the Company's fertilizer products to agricultural customers are
typically seasonal in nature and usually result in the Company's generating a
greater amount of net sales and operating income in the spring (the Company's
fourth fiscal quarter). The Company has reduced its seasonal exposure to the
agricultural market over the last several fiscal years by increasing the
percentage of its net sales to industrial customers whose purchases are more
evenly spread over the Company's fiscal year. The Company anticipates that the
percentage of net sales to industrial customers will continue to increase over
the next several fiscal years.

FINANCIAL INFORMATION ABOUT FOREIGN AND DOMESTIC OPERATIONS AND EXPORT SALES

        The amount of revenue attributable to the Company's sales to foreign
markets over the last three fiscal years and value of the Company's assets
located outside the United States over the last three fiscal years is set forth
in the Company's 1999 Annual Report to Shareholders under the caption "Note
12-Segment Information" contained in the "Notes to Consolidated Financial
Statements," which information is incorporated herein by reference.

OUTLOOK AND UNCERTAINTIES

        Except for the historical statements and discussions, statements set
forth in this report may constitute "forward-looking statements" within the
meaning of Section 21E of the Securities Exchange Act of 1934, as amended. In
some cases, forward-looking statements can be identified by the use of
terminology such as "may," "will," "expects," "believes," "plans,"
"anticipates," "estimates," "potential," or "continue," the negatives thereof or
other comparable terminology. Since these forward-looking statements rely on a
number of assumptions concerning future events, risks and other uncertainties
that are beyond the Company's ability to control or predict with certainty,
actual results may differ materially from such forward-looking statements.
Future events, risks and uncertainties that could cause a material difference in
such results include, but are not limited to:

        Factors Affecting Fertilizer Demand and Prices. With virtually all of
its nitrogen net sales and approximately 78% of its total net sales in fiscal
1999 derived from domestic markets, the Company's operating results are highly
dependent upon conditions in the U.S. agricultural industry. A variety of
factors beyond the Company's control can materially affect domestic fertilizer
demand and pricing. These factors include, but are not limited to, futures
prices for crops that require significant fertilizer application, U.S. planted
acreage, government agricultural policies, projected grain stocks, crop failure,
weather, changing or unpredictable crop choices by farmers and changes in
agricultural production methods. Since fertilizers, particularly anhydrous
ammonia and urea, are also used for industrial applications, industrial markets
and the general economy can also affect product demand and prices.

        International market conditions also significantly influence the
Company's operating results. The market for fertilizers is influenced by such
factors as the relative value of the U.S. dollar and its impact upon the cost of
importing or exporting fertilizers; foreign agricultural policies; the existence
of, or changes in, import or foreign currency exchange barriers in certain
foreign markets; changes in the hard currency demands of certain countries; and
other regulatory policies of foreign governments, as well as the laws and
policies of the United States affecting foreign trade and investment. The
Company is also

                                       12
<PAGE>   13

subject to general risks of doing business abroad, including risks associated
with economic or political instability.

        As is evidenced by current depressed prices for nitrogen fertilizers and
the recent drop in the price of phosphatic fertilizers, fertilizer prices can be
extremely volatile, with significant price changes from one growing season to
the next. Fertilizers are global commodities and can be subject to intense price
competition from domestic and foreign sources. No assurance can be given that
average realized prices paid for the Company's fertilizer products will be at
any given level.

        Seasonality. The usage of fertilizer for agricultural application is
seasonal, and the Company's quarterly results reflect the fact that, in its
markets, significantly more fertilizer is customarily purchased in the spring.
In most years, substantial portions of the Company's net sales and operating
income are generated in the last four months of its fiscal years (March through
June). Quarterly results can vary significantly from one year to the next due
primarily to weather-related shifts in planting schedules and purchase patterns.
The Company incurs appreciable expenditures for fixed costs throughout the year
and for inventory in advance of the spring planting season.

        Dependence on Natural Gas. Natural gas is the primary raw material used
in the manufacture of nitrogen products. Natural gas is used as both a chemical
feedstock and a fuel to produce anhydrous ammonia, which is then used in the
production of all other nitrogen products. Anhydrous ammonia is also a raw
material in the production of DAP. Accordingly, the Company's profitability is
dependent upon the price and availability of natural gas. A significant increase
in the price of natural gas (such as the recent increase that began in the
summer of 1999) that is not recovered through an increase in the price of the
Company's nitrogen products, or an extended interruption in the supply of
natural gas to its production facilities, will have a material adverse effect on
its results of operations and financial condition.

        Environmental Regulations. The Company is subject to various
environmental laws and regulations of federal, state and local governments.
Significant capital expenditures and operating costs have been incurred and will
continue to be incurred as a result of these laws and regulations. The Company
cannot predict or quantify the impact of new or changed laws or regulations. In
the normal course of business, the Company is exposed to risks such as possible
release of hazardous substances into the environment. Such releases could cause
substantial damage or injuries and result in material costs to the Company.

        Competition. Fertilizer products are global commodities, and customers
base their purchasing decisions principally on the delivered price of the
product. As a result, markets for the Company's products are highly competitive.
A number of U.S. producers compete with the Company in domestic and export
markets, and producers in other countries, including state-owned and
government-subsidized entities, compete with the Company in the United States
and in foreign markets to which the Company exports. Many of the Company's
competitors are larger and have greater financial resources than the Company.

        Year 2000 Issues. The information regarding the Company's efforts
relating to Year 2000 issues is set forth in the Company's 1999 Annual Report to
Shareholders under the caption "Year 2000" in "Management's Discussion and
Analysis of Financial Condition and Results of Operation," which information is
incorporated herein by reference.

                                       13
<PAGE>   14

ITEM 2.   PROPERTIES

        The Company owns its corporate headquarters in Yazoo City that contains
approximately 65,000 square feet of office space.

        The Company owns production plants in Yazoo City and Pascagoula,
Mississippi; Donaldsonville, Louisiana; and Carlsbad, New Mexico, which are
complete with necessary support facilities, such as roads, railroad tracks,
storage, offices, laboratories, warehouses, machine shops, and loading
facilities. Adequate supplies of water and electric power are available at all
locations. In addition to the fertilizer storage facilities at Yazoo City and
Pascagoula, Mississippi; Carlsbad, New Mexico; and Donaldsonville, Louisiana,
the Company also owns or leases 32 major storage and distribution facilities at
other locations in Alabama, Arkansas, California, Georgia, Indiana, Kentucky,
Louisiana, Mississippi, Missouri, Ohio, Tennessee, and Texas, with a total
system-wide storage capacity of approximately 315,000 tons.

ITEM 3.   LEGAL PROCEEDINGS

        CLEVE REBER CERCLA SITE. The Company has received and responded to
letters issued by the U.S. Environmental Protection Agency ("EPA") under Section
104 of the Comprehensive Environmental Response, Compensation and Liability Act
("CERCLA") relative to the possible disposition of waste by the Company at the
disposal site identified as the Cleve Reber site in Ascension Parish, Louisiana.
It is the Company's position that, based upon available information and records,
the Company did not utilize the Cleve Reber site for the disposition of
hazardous material, and it does not appear that the Company has any
responsibility for investigation and cleanup on this site. It should be noted
that the EPA is contemplating an action under the Resource Conservation and
Recovery Act, Section 7003, as well as the CERCLA action mentioned above. The
EPA has issued Section 106 orders against the major contributors at the site for
cleanup, not including the Company. They are now engaged in negotiations for
cleanup. In 1994, the Company received a supplemental 104(e) request for
information from the EPA, indicating the EPA's renewed interest in pursuing
Potential Responsible Persons at the site. The Company responded, but has
received no further requests from the EPA.

        TERRA INTERNATIONAL, INC. On August 31, 1995, the Company filed suit in
federal court in Mississippi against Terra International, Inc. ("Terra"),
seeking a declaratory judgment and other relief, establishing that certain
technology relating to the design of an ammonium nitrate neutralizer which the
Company licensed to Terra is not defective and was not the cause of an explosion
which occurred in 1994 at Terra's Port Neal, Iowa, fertilizer facility. The
Company is also seeking an unspecified amount of monetary damages for defamation
based on Terra's public statement related to the Company's alleged role in the
explosion. Also, on August 31, 1995, Terra filed suit in federal court in Iowa
against the Company seeking to recover a total of approximately $300 million in
property damage, lost profits and other out-of-pocket expenses allegedly caused
by the explosion. Terra alleges that the ammonium nitrate neutralizer technology
licensed to Terra was defectively designed by the Company and that the design
defect caused the Port Neal explosion. It has been conclusively determined that
the Mississippi federal district court is the proper venue to resolve all issues
between the parties relating to the Port Neal explosion. Discovery is nearly
complete and a trial date of May 15, 2000, has been set by the court. The
Company does not anticipate that the outcome of this matter will have a material
impact on its financial position or future earnings.

ITEM 4.   SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

        None.

                                       14
<PAGE>   15

                                     PART II

ITEM 5.   MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED
          STOCKHOLDER MATTERS

        The information required by this item is set forth in the Company's 1999
Annual Report to Shareholders under the caption "Quarterly Results," contained
in "Management's Discussion and Analysis of Financial Condition and Results of
Operations," which information is incorporated herein by reference.

ITEM 6.   SELECTED FINANCIAL DATA

        The information required by this item is set forth in the Company's 1999
Annual Report to Shareholders under the caption "Financial Highlights," which
information is incorporated herein by reference.

ITEM 7.   MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
          AND RESULTS OF OPERATIONS

        The information required by this item is set forth in the Company's 1999
Annual Report to Shareholders under the caption "Management's Discussion and
Analysis of Financial Condition and Results of Operations," which information is
incorporated herein by reference.

ITEM 7A.  MARKET RISK

        The information required by this item is set forth in the Company's 1999
Annual Report to Shareholders under the caption "Market Risk," which information
is incorporated herein by reference.

ITEM 8.   FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

        The consolidated financial statements, together with the report thereon
of Arthur Andersen LLP dated July 28, 1999, appearing in the Company's 1999
Annual Report to Shareholders, are incorporated herein by reference.

ITEM 9.   CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON
          ACCOUNTING AND FINANCIAL DISCLOSURE

        None.

                                       15
<PAGE>   16

                                    PART III

ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT

  (a)   The information required by this item regarding directors is set forth
in the Company's Proxy Statement for the 1999 Annual Meeting of Shareholders
under the captions "Nominees for Election to Serve Until 2002," "Directors
Continuing to Serve Until 2001," and "Directors Continuing to Serve Until 2000,"
which information is incorporated herein by reference.

  (b)   Executive officers are elected for a one-year term by the Board of
Directors. The Company's executive officers are as follows:

<TABLE>
<CAPTION>
                                                               OFFICE AND EMPLOYMENT DURING THE
NAME OF OFFICER                  AGE                                 LAST FIVE FISCAL YEARS
------------------------------          -----------------------------------------------------------------------
<S>                              <C>        <C>
Charles O. Dunn                  51         President and Chief Executive Officer since April 1, 1993; Executive
                                            Vice President (1988-1993)

C. E. McCraw                     51         Senior Vice President-Operations since July 12, 1994; Senior Vice
                                            President-Fertilizer Group (1991-1994)

Robert E. Jones                  51         Senior Vice President-Corporate Development effective October 1, 1997;
                                            Senior Vice President and General Counsel (1996-1997); Vice President
                                            and General Counsel (1989-1996)

David W. Arnold                  62         Senior Vice President-Technical Group since July 1, 1991

Timothy A. Dawson                45         Senior Vice President and Chief Financial Officer since April 22,
                                            1999; Vice President-Finance (1996-1999); Director of Finance
                                            (1993-1996)

Ethel Truly                      49         Vice President-Administration since January 18, 1996; Director of
                                            Administrative Services (1995-1996); Assistant General Counsel
                                            (1985-1995)

William L. Smith                 49         Vice President and General Counsel since November 11, 1998; General
                                            Counsel (1997-1998); partner in the law firm of Brunini, Grantham,
                                            Grower & Hewes, PLLC (1982-1997)

Jerry W. Irwin                   58         Vice President-Nitrogen Production since October 15, 1998; General
                                            Manager of Yazoo City facility (1986-1998)

Joe A. Ewing                     48         Vice President-Marketing and Distribution since September 1, 1999;
                                            Director of Marketing and Distribution (1998-1999); Director of
                                            Converted Nitrogen Sales (1997-1998); Director of Procurement and
                                            Distribution (1993-1997)
</TABLE>

  (c)   The information called for with respect to the identification of
certain significant employees is not applicable to the Company.

  (d)   There are no family relationships among the directors and executive
officers listed above. There are no arrangements or understandings between any
named officer and any other person pursuant to which such person was selected as
an officer.


                                       16
<PAGE>   17

        The information required by this item regarding compliance with Section
16(a) of the Exchange Act is set forth in the Company's Proxy Statement for the
1999 Annual Meeting of Shareholders under the caption "Compliance with Section
16(a) of the Exchange Act," which information is incorporated herein by
reference.

ITEM 11.  EXECUTIVE COMPENSATION

        The information required by this item is set forth in the Company's
Proxy Statement for the 1999 Annual Meeting of Shareholders under the captions
"Compensation Committee Report on Executive Compensation" and "Executive
Compensation," which information is incorporated herein by reference.

ITEM 12.  SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

        The information required by this item is set forth in the Company's
Proxy Statement for the 1999 Annual Meeting of Shareholders under the caption
"Management Ownership of the Company's Stock," which information is incorporated
herein by reference.

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

        The information required by this item is set forth in the Company's
Proxy Statement for the 1999 Annual Meeting of Shareholders under the caption
"Board of Directors and Committees," which information is incorporated herein by
reference.


                                       17
<PAGE>   18

                                     PART IV

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

  (a)   FINANCIAL STATEMENTS AND SCHEDULES

        The consolidated financial statements, together with the report thereon
of Arthur Andersen LLP dated July 28, 1999, appearing in the 1999 Annual Report
to Shareholders, are incorporated by reference in this Form 10-K. With the
exception of the aforementioned information and information incorporated by
reference in Items 1, 5, 6, 7, 7A and 8, the 1999 Annual Report to Shareholders
is not to be deemed filed as part of this Form 10-K. Financial statement
schedules not included in this Form 10-K have been omitted because they are not
applicable or the required information is shown in the financial statements or
notes thereto. Separate financial statements of 50% or less owned persons
accounted for by the equity method that are not shown herein have been omitted
because, if considered in the aggregate, they would not constitute a significant
subsidiary.

          Financial Statements:

            Report of Independent Public Accountants

            Consolidated Balance Sheets, June 30, 1999 and 1998

            Consolidated Statements of Income, Years Ended June 30, 1999,
            1998 and 1997

            Consolidated Statements of Shareholders' Equity, Years Ended
            June 30, 1999, 1998 and 1997

            Consolidated Statements of Cash Flows, Years Ended June 30, 1999,
            1998 and 1997

            Notes to Consolidated Financial Statements


                                       18
<PAGE>   19

  (b)   EXHIBITS:

        Exhibits filed as part of this report are listed below. Certain exhibits
have been filed previously with the Commission and are incorporated herein by
reference.

           SEC EXHIBIT
           REFERENCE NO.            DESCRIPTION
           -------------            -----------

                2.1                 Asset Purchase Agreement, dated as of May
                                    21, 1996, by and among the Company,
                                    Mississippi Acquisition I, Inc., Mississippi
                                    Acquisition II, Inc., Eddy Potash, Inc., and
                                    New Mexico Potash Corporation; filed as
                                    Exhibit 2.1 to the Company's Current Report
                                    on Form 8-K filed September 3, 1996, SEC
                                    File No. 0-20411, and incorporated herein by
                                    reference.

                2.2                 Agreement and Plan of Merger and
                                    Reorganization, dated as of August 27, 1996,
                                    by and among the Company, MISS SUB, INC.,
                                    and First Mississippi Corporation; filed as
                                    Exhibit 2.2 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1996, SEC File No. 0-20411, and
                                    incorporated herein by reference.

                3.1                 Articles of Incorporation of the Company;
                                    filed as Exhibit 3.1 to the Company's
                                    Amendment No. 1 to Form S-1 Registration
                                    Statement filed August 2, 1994, SEC File No.
                                    33-53119, and incorporated herein by
                                    reference.

                3.2                 Bylaws of the Company; filed as Exhibit 3.2
                                    to the Company's Annual Report on Form 10-K
                                    for the fiscal year ended June 30, 1997, SEC
                                    File No. 0-20411, and incorporated herein by
                                    reference.

                4.1                 Shareholder Rights Plan; filed as Exhibit 1
                                    to the Company's Form 8-A Registration
                                    Statement dated August 15, 1994, SEC File
                                    No. 2-7803, and incorporated herein by
                                    reference.

                4.2                 Indenture dated as of November 25, 1997,
                                    between the Company and Harris Trust and
                                    Savings Bank, as Trustee, for the issuance
                                    of up to $300 million of debt securities;
                                    filed as Exhibit 4(a) to the Company's
                                    Current Report on Form 8-K filed November
                                    25, 1997, SEC File No. 001-12217, and
                                    incorporated herein by reference.

                4.3                 Indenture of Trust dated as of March 1,
                                    1998, between Mississippi Business Finance
                                    Corporation and Deposit Guaranty National
                                    Bank, for the issuance of bonds in the
                                    aggregate principal amount of $14.5 million
                                    to assist the Company in financing and
                                    refinancing the cost of construction and
                                    equipping of solid waste disposal facilities
                                    at its Pascagoula, Mississippi, facility;
                                    filed as Exhibit 4.3 to the Company's Annual
                                    Report on Form 10-K for the fiscal year
                                    ended June 30, 1998, SEC File No. 0-20411,
                                    and incorporated herein by reference.


                                       19
<PAGE>   20
<TABLE>
               <S>                  <C>
                10.1                Agreement made and entered into as of
                                    September 15, 1991, between Office Cherifien
                                    des Phosphates and the Company for the sale
                                    and purchase of phosphate rock; filed as
                                    Exhibit 10.1 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1991, File No. 2-7803, and incorporated
                                    herein by reference.

                10.2                Amendment No. 1, effective as of July 1,
                                    1992, to the Agreement effective as of
                                    September 15, 1991, between Office Cherifien
                                    des Phosphates and the Company for the sale
                                    and purchase of phosphate rock; filed as
                                    Exhibit 10.12 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1995, SEC File No. 2-7803, and
                                    incorporated herein by reference.(1)

                10.3                Amendment No. 2, effective as of July 1,
                                    1993, to the Agreement effective as of
                                    September 15, 1991, between Office Cherifien
                                    des Phosphates and the Company for the sale
                                    and purchase of phosphate rock; filed as
                                    Exhibit 10.11 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1995, SEC File No. 2-7803, and
                                    incorporated herein by reference.(2)

                10.4                Amendment No. 3, effective as of January 1,
                                    1995, to the Agreement effective as of
                                    September 15, 1991, between Office Cherifien
                                    des Phosphates and the Company for the sale
                                    and purchase of phosphate rock; filed as
                                    Exhibit 10.10 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1995, SEC File No. 2-7803, and
                                    incorporated herein by reference.(3)

                10.5                Amendment No. 4, effective as of January 1,
                                    1997, to the Agreement effective as of
                                    September 15, 1991, between Office Cherifien
                                    des Phosphates and the Company for the sale
                                    and purchase of phosphate rock; filed as
                                    Exhibit 10.8 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1997, SEC File No. 0-20411, and
                                    incorporated herein by reference.
</TABLE>

--------
         (1) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from the first and second
paragraphs of paragraph numbered 1 of Amendment No. 1, and an application for
confidential treatment has been filed separately with the Commission.
         (2) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from paragraphs numbered 5
and 8 of Amendment No. 2; from the first paragraph, paragraph numbered 1,
paragraph numbered 2, and paragraph numbered 3 of Schedule 1, Exhibit A; from
Schedule 2, Exhibit B; from Schedule 3, Exhibit C, and from Schedule 4, Exhibit
D; and an application for confidential treatment has been filed separately with
the Commission.
         (3) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from Schedule 1 to Amendment
No. 3, Exhibit B, and an application for confidential treatment has been filed
separately with the Commission.



                                       20
<PAGE>   21

                10.6                Credit Agreement dated as of November 25,
                                    1997, among the Company; the Lenders Party
                                    Thereto; Harris Trust and Savings Bank, as
                                    Administrative Agent; Bank of Montreal,
                                    Chicago Branch, as Syndication Agent; and
                                    Credit Agricole Indosuez, as Co-Agent,
                                    establishing the Company's $200 million
                                    revolving line of credit; filed as Exhibit
                                    10.6 to the Company's Annual Report on Form
                                    10-K for the fiscal year ended June 30,
                                    1998, SEC File No. 0-20411, and incorporated
                                    herein by reference.

                10.7                First Amendment, effective as of June 10,
                                    1999, to Credit Agreement dated as of
                                    November 25, 1997, among the Company; the
                                    Lenders Party Thereto; Harris Trust and
                                    Savings Bank, as Administrative Agent; Bank
                                    of Montreal, Chicago Branch, as Syndication
                                    Agent; and Credit Agricole Indosuez, as
                                    Co-Agent, establishing the Company's $200
                                    million revolving line of credit.

                10.8                Form of Severance Agreement dated July 29,
                                    1996, by and between the Company and each of
                                    its Executive Officers; filed as Exhibit
                                    10.14 to the Company's Annual Report on Form
                                    10-K for the fiscal year ended June 30,
                                    1996, SEC File No. 2-7803, and incorporated
                                    herein by reference.

                10.9                Mississippi Chemical Corporation Officer and
                                    Key Employee Incentive Plan; filed as
                                    Exhibit 10.8 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1998, SEC File No. 0-20411, and
                                    incorporated herein by reference.

                10.10               Mississippi Chemical Corporation Executive
                                    Deferred Compensation Plan; filed as Exhibit
                                    10.9 to the Company's Annual Report on Form
                                    10-K for the fiscal year ended June 30,
                                    1998, SEC File No. 0-20411, and incorporated
                                    herein by reference.

                10.11               Mississippi Chemical Corporation Nonemployee
                                    Directors' Deferred Compensation Plan; filed
                                    as Exhibit 10.10 to the Company's Annual
                                    Report on Form 10-K for the fiscal year
                                    ended June 30, 1998, SEC File No. 0-20411,
                                    and incorporated herein by reference.

                10.12               Mississippi Chemical Corporation
                                    Supplemental Benefit Plan, as amended and
                                    restated as of July 1, 1996; filed as
                                    Exhibit 10.11 to the Company's Annual Report
                                    on Form 10-K for the fiscal year ended June
                                    30, 1998, SEC File No. 0-20411, and
                                    incorporated herein by reference.

                10.13               Mississippi Chemical Corporation 1994 Stock
                                    Incentive Plan; filed as Exhibit 4.2 to the
                                    Company's Form S-8 Registration Statement
                                    filed December 21, 1995, SEC File No.
                                    33-65209, and incorporated herein by
                                    reference.

                                       21
<PAGE>   22

                10.14               Mississippi Chemical Corporation 1995 Stock
                                    Option Plan for Nonemployee Directors; filed
                                    as Exhibit 4.3 to the Company's Form S-8
                                    Registration Statement filed December 21,
                                    1995, SEC File No. 33-65209, and
                                    incorporated herein by reference.

                10.15               Mississippi Chemical Corporation 1995
                                    Restricted Stock Purchase Plan for
                                    Nonemployee Directors; filed as Exhibit 4.4
                                    to the Company's Form S-8 Registration
                                    Statement filed December 21, 1995, SEC File
                                    No. 33-65209, and incorporated herein by
                                    reference.

                13.1                Portions of the Company's 1999 Annual Report
                                    to Shareholders as referenced in this Form
                                    10-K for the fiscal year ending June 30,
                                    1999.

                21                  List of subsidiaries of the Company.

                23                  Consent of Arthur Andersen LLP.

                27                  Financial Data Schedule.

  (c)   REPORTS ON FORM 8-K:

        No reports were filed on Form 8-K during the three months ended June
30, 1999.


                                       22
<PAGE>   23


                                   SIGNATURES

        Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

                                            MISSISSIPPI CHEMICAL CORPORATION

                                            By:  /s/ Charles O. Dunn
                                                 ---------------------------
                                                 Charles O. Dunn
                                                 Principal Executive Officer

                                            By:  /s/ Timothy A. Dawson
                                                 ---------------------------
                                                 Timothy A. Dawson
                                                 Principal Financial Officer and
                                                 Chief Accounting Officer
Date:    September 28, 1999

        Pursuant to the requirements of the Securities Exchange Act of 1934,
this report has been signed below by the following persons on behalf of the
Registrant and in the capacities and on the dates indicated.

<TABLE>
<CAPTION>

SIGNATURE                                TITLE                                        DATE

<S>                                      <C>                                          <C>
/s/ Charles O. Dunn                      Director,                                    September 28, 1999
----------------------------             President and Chief Executive Officer
Charles O. Dunn                          (principal executive officer)

/s/ Coley L. Bailey                      Director, Chairman of the Board              September 28, 1999
----------------------------
Coley L. Bailey

/s/ John Sharp Howie                     Director, Vice Chairman of the Board         September 28, 1999
----------------------------
John Sharp Howie

/s/ John W. Anderson                     Director                                     September 28, 1999
----------------------------
John W. Anderson

/s/ Haley Barbour                        Director                                     September 28, 1999
---------------------------
Haley Barbour

/s/ Frank R. Burnside, Jr.               Director                                     September 28, 1999
----------------------------
Frank R. Burnside, Jr.

/s/ W. R. Dyess                          Director                                     September 28, 1999
---------------------------
W. R. Dyess

/s/ Woods E. Eastland                    Director                                     September 28, 1999
----------------------------
Woods E. Eastland

/s/ George D. Penick, Jr.                Director                                     September 28, 1999
----------------------------
George D. Penick, Jr.

/s/ W. A. Percy II                       Director                                     September 28, 1999
----------------------------
W. A. Percy II

/s/ David M. Ratcliffe                   Director                                     September 28, 1999
----------------------------
David M. Ratcliffe

/s/ Wayne Thames                         Director                                     September 28, 1999
----------------------------
Wayne Thames
</TABLE>



                                       23
<PAGE>   24
                        MISSISSIPPI CHEMICAL CORPORATION

                                  EXHIBIT INDEX
                                       TO
                                    FORM 10-K

<TABLE>
<CAPTION>
 EXHIBIT                                                              PAGE
  NUMBER                  DESCRIPTION                                NUMBER
 -------  --------------------------------------------------------   ------
<S>                                                                  <C>
  2.1     Asset Purchase Agreement, dated as of May 21, 1996, by and
          among the Company, Mississippi Acquisition I, Inc.,
          Mississippi Acquisition II, Inc., Eddy Potash, Inc., and New
          Mexico Potash Corporation; filed as Exhibit 2.1 to the
          Company's Current Report on Form 8-K filed September 3, 1996,
          SEC File No. 0-20411, and incorporated herein by reference.

  2.2     Agreement and Plan of Merger and Reorganization, dated as of
          August 27, 1996, by and among the Company, MISS SUB, INC., and
          First Mississippi Corporation; filed as Exhibit 2.2 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1996, SEC File No. 0-20411, and incorporated herein
          by reference.

  3.1     Articles of Incorporation of the Company; filed as Exhibit 3.1
          to the Company's Amendment No. 1 to Form S-1 Registration
          Statement filed August 2, 1994, SEC File
          No. 33-53119, and incorporated herein by reference.

  3.2     Bylaws of the Company; filed as Exhibit 3.2 to the Company's
          Annual Report on Form 10-K for the fiscal year ended June 30,
          1997, SEC File No. 0-20411, and incorporated herein by
          reference.

  4.1     Shareholder Rights Plan; filed as Exhibit 1 to the Company's
          Form 8-A Registration Statement dated August 15, 1994, SEC
          File No. 2-7803, and incorporated herein by reference.

  4.2     Indenture dated as of November 25, 1997, between the Company
          and Harris Trust and Savings Bank, as Trustee, for the
          issuance of up to $300 million of debt securities; filed as
          Exhibit 4(a) to the Company's Current Report on Form 8-K filed
          November 25, 1997, SEC File No. 001-12217, and incorporated
          herein by reference.

  4.3     Indenture of Trust dated as of March 1, 1998, between
          Mississippi Business Finance Corporation and Deposit Guaranty
          National Bank, for the issuance of bonds in the aggregate
          principal amount of $14.5 million to assist the Company in
          financing and refinancing the cost of construction and
          equipping of solid waste disposal facilities at its
          Pascagoula, Mississippi, facility; filed as Exhibit 4.3 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1998, SEC File No. 0-20411, and incorporated herein
          by reference.
</TABLE>

                                       24
<PAGE>   25


  10.1    Agreement made and entered into as of September 15, 1991,
          between Office Cherifien des Phosphates and the Company for
          the sale and purchase of phosphate rock; filed as Exhibit 10.1
          to the Company's Annual Report on Form 10-K for the fiscal
          year ended June 30, 1991, File No. 2-7803, and incorporated
          herein by reference.

  10.2    Amendment No. 1, effective as of July 1, 1992, to the
          Agreement effective as of September 15, 1991, between Office
          Cherifien des Phosphates and the Company for the sale and
          purchase of phosphate rock; filed as Exhibit 10.12 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1995, SEC File No. 2-7803, and incorporated herein by
          reference.(4)

  10.3    Amendment No. 2, effective as of July 1, 1993, to the
          Agreement effective as of September 15, 1991, between Office
          Cherifien des Phosphates and the Company for the sale and
          purchase of phosphate rock; filed as Exhibit 10.11 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1995, SEC File No. 2-7803, and incorporated herein by
          reference.(5)

  10.4    Amendment No. 3, effective as of January 1, 1995, to the
          Agreement effective as of September 15, 1991, between Office
          Cherifien des Phosphates and the Company for the sale and
          purchase of phosphate rock; filed as Exhibit 10.10 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1995, SEC File No. 2-7803, and incorporated herein by
          reference.(6)

  10.5    Amendment No. 4, effective as of January 1, 1997, to the
          Agreement effective as of September 15, 1991, between Office
          Cherifien des Phosphates and the Company for the sale and
          purchase of phosphate rock; filed as Exhibit 10.8 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1997, SEC File No. 0-20411, and incorporated herein
          by reference.


--------

          (4) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from the first and second
paragraphs of paragraph numbered 1 of Amendment No. 1, and an application for
confidential treatment has been filed separately with the Commission.
          (5) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from paragraphs numbered 5
and 8 of Amendment No. 2; from the first paragraph, paragraph numbered 1,
paragraph numbered 2, and paragraph numbered 3 of Schedule 1, Exhibit A; from
Schedule 2, Exhibit B; from Schedule 3, Exhibit C, and from Schedule 4, Exhibit
D; and an application for confidential treatment has been filed separately with
the Commission.
          (6) Pursuant to the Securities Exchange Act of 1934, Rule 24b-2,
confidential business information has been deleted from Schedule 1 to Amendment
No. 3, Exhibit B, and an application for confidential treatment has been filed
separately with the Commission.


                                       25
<PAGE>   26
<TABLE>
<S>       <C>                                                               <C>
  10.6    Credit Agreement dated as of November 25, 1997, among the
          Company; the Lenders Party Thereto; Harris Trust and Savings
          Bank, as Administrative Agent; Bank of Montreal, Chicago
          Branch, as Syndication Agent; and Credit Agricole Indosuez, as
          Co-Agent, establishing the Company's $200 million revolving
          line of credit; filed as Exhibit 10.6 to the Company's Annual
          Report on Form 10-K for the fiscal year ended June 30, 1998,
          SEC File No. 0-20411, and incorporated herein by reference..

  10.7    First Amendment, effective as of June 10, 1999, to Credit          [ ]
          Agreement dated as of November 25, 1997, among the
          Company; the Lenders Party Thereto; Harris Trust and Savings
          Bank, as Administrative Agent; Bank of Montreal, Chicago
          Branch, as Syndication Agent; and Credit Agricole Indosuez, as
          Co-Agent, establishing the Company's $200 million revolving
          line of credit.

  10.8    Form of Severance Agreement dated July 29, 1996, by and
          between the Company and each of its Executive Officers; filed
          as Exhibit 10.14 to the Company's Annual Report on Form 10-K
          for the fiscal year ended June 30, 1996, SEC File No. 2-7803,
          and incorporated herein by reference.

  10.9    Mississippi Chemical Corporation Officer and Key Employee
          Incentive Plan; filed as Exhibit 10.8 to the Company's Annual
          Report on Form 10-K for the fiscal year ended June 30, 1998,
          SEC File No. 0-20411, and incorporated herein by reference.

  10.10   Mississippi Chemical Corporation Executive Deferred
          Compensation Plan; filed as Exhibit 10.9 to the Company's
          Annual Report on Form 10-K for the fiscal year ended June 30,
          1998, SEC File No. 0-20411, and incorporated herein by
          reference.

  10.11   Mississippi Chemical Corporation Nonemployee Directors'
          Deferred Compensation Plan; filed as Exhibit 10.10 to the
          Company's Annual Report on Form 10-K for the fiscal year ended
          June 30, 1998, SEC File No. 0-20411, and incorporated herein
          by reference.

  10.12   Mississippi Chemical Corporation Supplemental Benefit Plan, as
          amended and restated as of July 1, 1996; filed as Exhibit
          10.11 to the Company's Annual Report on Form 10-K for the
          fiscal year ended June 30, 1998, SEC File No. 0-20411, and
          incorporated herein by reference.

  10.13   Mississippi Chemical Corporation 1994 Stock Incentive Plan;
          filed as Exhibit 4.2 to the Company's Form S-8 Registration
          Statement filed December 21, 1995, SEC File No. 33-65209, and
          incorporated herein by reference.
</TABLE>


                                       26
<PAGE>   27

  10.14   Mississippi Chemical Corporation 1995 Stock Option Plan for
          Nonemployee Directors; filed as Exhibit 4.3 to the Company's
          Form S-8 Registration Statement filed December 21, 1995, SEC
          File No. 33-65209, and incorporated herein by reference.

  10.15   Mississippi Chemical Corporation 1995 Restricted Stock
          Purchase Plan for Nonemployee Directors; filed as Exhibit 4.4
          to the Company's Form S-8 Registration Statement filed
          December 21, 1995, SEC File No. 33-65209, and incorporated
          herein by reference.

  13.1    Portions of the Company's 1999 Annual Report to Shareholders     [ ]
          as referenced in this Form 10-K for the fiscal year ending
          June 30, 1999.

   21     List of subsidiaries of the Company.                             [ ]

   23     Consent of Arthur Andersen LLP.                                  [ ]

   27     Financial Data Schedule.                                         [ ]


                                       27