Instead of carrying bags, empty the bags in an attachment fixed on the forks and use it to dump about 3 ons at a time, use a larger capacity forklift

attachment details
http://www.toolfetch.com/fork-truck-attachments-ves-d-33-hd.shtml

You would need to confirm that with your Nissan representative. Give him the dimensions of teh bag & maximum weight, etc etc

Dear John,
The Bulk bag is also on the cards, can the 2.5 ton handle a 800-1000kg bulk bag due to dementions on the bag ?

I am not familarir wit hthe Cool tyre concept but sounds like it might provide shock absorbtion. In North America the soft inner core tyre we call "Super Soft" made by Main Tire co in teh state of Maine are very common. In your area they might be referred to as elastic tyres.
Your biggest issue will be "corrosion" the fertilizer dust on the floors will be kick up in the air by the forklifts tyres. and settle all over the forklift & humidity will make it stick like glue to the forklift. Like I stated before, grease & lubricate, clean or replace the engine air filter often, inspect the brake system periodically - meaning remove the front tyers & brake drums the fertilizer dust will get in there & deterioate the cables &, springs & linkage. Wash teh unit down thoroughly. Get advise from your dealer on how to wash the unit down - there are a lot of electronic devises on todays forklift & moister can harm them. Make cert all celectrical connectors & exposed terminals are thoroughly grease with a diaelectric grease (non conductive ).
Dust prtect will help but corrosion protect will be better

Thank you John for your reply.
Im plaing on going for the Dust specification
Over head exanst mufler (So exhaust will not create more dust)
And there is a Cool tyre called Airboss tyres (solid tyre with holes gone horizontaly so it will absorbed shock)
Any idea about the Airboss tyre wear pattern ? are they good ? (Just saw on the brochure)

And as for maintenance will i need to keep a spare radiator for the job ?

What would be the problem areas when it comes to maintenance that i should be aware of ?

The Nissan will work just fine as any lift truck in your application. Being in a fertilizer enviroment means you will have a lot of maintanence issues no matter what brand you use - the dust get into everything. Have the unit PM very frequently - oil, grease, filters, cable checked and terminal s/cconnectors coated with a dielectric grease. Blow the unit off with compressed air daily will help some.. Oil/grease is cheaper than metal. Things like parking brake cables will freeze up.
Would recommend you have the forklift fitted with solid "soft ride" type tyres to reduce road shock transmission - tehy cost a little more but well worth the investment.
I know that many of the Japanese brands have a special option for forklifts working in fisheries where they are exposed to briney water this can help in a fertilizer plant too.
Would not recommend any type of electric unit for this application - fertizer dust will not only get in the controls but motors connectros & you'll have more issues than you want. Especially, in a humid climate. All that savings for electrics is true in a "normal & clean" work site with smooth floors. For extended operating hours you would need spare batteries & a battery change out station.
Since fertilizer dust is explosive you might want to check with your local authorities what type of safety rating the truck will require. In the US we have governmental regulations like this.
You may want to conside more than one forklift. Should your forklift be down for mainteance or repair you have no "back-up" & you are shutdown.

One more thing the the working area surface is not good