One of the country's two big fertiliser co-operatives has warned that international demand is putting fertiliser prices under pressure again.
Ravensdown chief executive Rodney Green says the growing worldwide demand for food and energy is strengthening fertiliser commodity prices.
He says the urea price has increased by $US100 a tonne since September, DAP has almost doubled in price since November 2009 and sulphur, which is commonly about $US50 a tonne, has risen to about $US200.
Shipping charges have also increased.
Ravensdown says with that pressure it is unsure how long it can hold the prices it charges farmers.