Australia's richest woman invests $300 mln in UK fertiliser firm

* Share (LSE: SHRE.L - news) price up 3.6 percent

* Analysts see possible upside potential from polyhalite price (Adds context, comment)

SYDNEY, Oct (Shenzhen: 000069.SZ - news) 25 (Reuters) - Hancock Prospecting (Pty) Ltd, controlled by Australian billionaire iron ore magnate Gina Rinehart, on Tuesday said it was investing $300 million in British fertiliser business Sirius Minerals Plc (Other OTC: SRUXF - news) as it moves deeper into agriculture.

Hancock said Sirius could become one of the world's leading producers of multi-nutrient fertiliser.

The company, which has a market capitalisation of 792 million pounds according to Reuters data, is developing a polyhalite project in North Yorkshire in the United Kingdom.

"This fits with my approach of investing in strategic areas for the long term, and I hope the product is of assistance to many Australian farmers," Rinehart said in a statement.

Sirius Chief Executive Chris Fraser said Hancock's investment would bring mining and agricultural sector expertise to the operation.

Polyhalite is a naturally occurring mineral containing four of the six nutrients that ensure plant growth - potassium, sulphur, magnesium and calcium.

In a note Shore Capital, which rates Sirius a buy, said the polyhalite price could be a significant source of upside as yields being demonstrated in crop trials suggest it could command a premium.

It called Rinehart's backing "a resounding endorsement" and said it expected the conclusion of stage one financing this year. A further $800 million will need to be raised.

Sirius' share price was up 3.6 percent by 1133 GMT.

Hancock is also in a joint $278 million bid with China's Shanghai CRED Real Estate for Australia's biggest cattle empire, S. Kidman & Co.

Rinehart is attempting to persuade the Kidman cattle empire that her offer remains superior after a group of four wealthy graziers, known as BBHO, made a A$386 million ($294 million) bid.

($1 = 1.3120 Australian dollars) (Reporting by James Regan; additional reporting by Barbara Lewis in London; editing by Christian Schmollinger and Jason Neely)