Crop Study Update

28 August 2012

Sirius Minerals Plc

Crop Study Update

§ First growing season complete for multi-year crop study conducted with Texas A&M University and USDA-ARS Scientists

§ Crop study to validate the product performance (tonne for tonne) of Sulphate of Potash ("SOP") as a premium source of potassium and sulphur compared to the more common Muriate of Potash ("MOP")

§ Early results indicate that yields of SOP treated crops were higher than MOP treated crops, and SOP treated crops outperformed MOP treated crops for important quality benefits

§ Second growth cycle to include direct application of Polyhalite to study the expected benefits of this potentially bulk source of organic potassium, sulphur, magnesium and calcium

The Directors of Sirius Minerals Plc (AIM: SXX, OTCQX: SRUXY) ("Sirius" or the "Company"), the globally diversified Potash development group, are pleased to provide results from the first growing season of a multi-year crop study with Texas A&M University and the USDA-ARS, Beltsville, MD that commenced in January 2012.

Chris Fraser, Managing Director and CEO of Sirius said:

"Sirius commissioned this study to demonstrate the product performance of SOP as a premium source of potassium and sulphur. Most studies have focused on the lower potassium content of SOP compared to MOP and as a result we felt they did not properly account for the benefits of the added sulphur over the costs of the chloride in MOP.

"The first growing cycle has delivered very encouraging results on both yield and quality. If these results continue, they will help validate our long-held view that SOP can have a much larger share of the potash market and justify a significant performance based premium."

Purpose of the Crop Study

The purpose of the crop study is to quantify the benefits of SOP compared to MOP on the basis of equivalent fertiliser product amounts, i.e. on a tonne-for-tonne basis, at various application levels. Irish potatoes, chilli peppers and grain sorghum were selected for this study to represent three broad crop types in the developing world such as Asia, Africa and Latin America as well as the first world countries. A combination of greenhouse and field trials will both investigate the effects of the various fertiliser sources (SOP and MOP), and the advantages of different application methods (soil versus foliar) and application timing.

 Preliminary Results

Results from the first growing season indicate that yields of potassium treated crops were higher than those of controls. In addition, yields of all SOP-treated crops were higher than those of MOP-treated at application levels higher than 45kg/ha. The benefits of the sulphur in SOP coupled with negative effects of chloride in MOP were evident in yield and quality responses.

The quality benefits of potassium fertilisation included: faster ripening, intense colour development, increased fruit firmness and hence longer shelf life, increased starch concentration in potato tubers and sorghum grains, and lower levels of reducing sugars in potato tubers. SOP treated crops outperformed MOP-treated crops for the quality benefits of higher total ascorbic acid (vitamin C) and lower dehydro ascorbic acid (a plant stress indicator) in peppers, higher starch and lower reducing sugar concentrations in potatoes, and higher starch and protein and lower tannin concentrations in sorghum grain.

Polyhalite Added to Studies

In the second growing cycle direct application Polyhalite will be added to the study set-up. The hypothesis is that the unique balanced, multi-nutrient nature of Polyhalite will show yield and quality results. Sirius believes that Polyhalite has some very unique performance benefits and represents potentially a valuable organic bulk multi-nutrient fertiliser.

Balanced fertilisation is widely regarded as a key part of the solution to the issues of food security and malnutrition. Preliminary analysis of the major agricultural regions in the world show significant deficiencies in the core components of Polyhalite (potassium, sulphur and magnesium). Large areas of Africa, Brazil, China, and India all have known nutrient deficiencies that are not being adequately addressed. Polyhalite represents a unique natural, and hence organic, blend of four vital macro nutrients (potassium, sulphur, magnesium and calcium) that York Potash can potentially produce in bulk quantities.

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About Sirius Minerals Plc

Sirius Minerals is a globally diversified Potash development company. Its primary focus is to bring on stream major Potash mining facilities through the acquisition and development of projects overlying recognised Potash deposits. It is developing the flagship York Potash Project in North Yorkshire, United Kingdom and holds properties in the United States and Australia. Incorporated in 2003, Sirius Minerals' shares are traded on the London Stock Exchange's AIM market. Its shares are also traded in the United States on the OTCQX through a sponsored ADR facility. Further information on the Company can be found at www.siriusminerals.com