The spectre of export bans returned to grain markets, with rumours of curbs by both Russia, whose strong pace of shipments threatens to trigger a government cut-off, and by drought-struck Argentina.

The threat of a Russian restrictions, which Agrimoney.com flagged on Monday, thanks to the strong pace of exports was highlighted on both sides of the Atlantic.

In the UK, grain traders at a major commodities house, with a strong Black Sea presence, noted "talk that Russia could impose an export tax before the end of the season [in June] to stem the flow of wheat", so shifting import orders to other exporting countries.

In the US, speculation was of restrictions being imposed in March or April, when exports may have reached the 23m-25m-tonne threshold at which Russian leaders have pledged to impose curbs to protect domestic supplies.

Argentine downgrades

Separately, rumours kicked off that Argentina may also curb exports after drought damage to its corn and soybean crops, which have prompted a series of downgrades to estimates for the crops.

On Tuesday, Oil World, for a second successive week, cut its forecast for the Argentine soybean crop, this time by 1.5m tonnes to 48.5m tonnes, taking an improvement from last season's 49.2m-tonne crop off the agenda.

The United Nations food agency, the Food and Agriculture Organization forecast an Argentine corn harvest of 21.4m tonnes, well below the latest estimate of 26.0m tonnes from the US Department of Agriculture, and last year's harvest of some 29m tonnes.

The downgrades followed a cut by Argentina's farm ministry of 7m tonnes, to 23m tonnes, in its estimate for the corn harvest, and to 48.9m tonnes, from 52m-53m tonnes, in the soybean crop.

'Rumours are out there' 

Rumours of a ban "are out there", Don Roose, president of US Commodities, told Agrimoney.com.

Argentina has a history of strong controls over crop exports, and in 2006 former president Néstor Kirchner, the late husband of current president Cristina Fernández de Kirchner, banned beef shipments in a bid to keep domestic prices in check.

However, farm minister Lorenzo Basso said on Tuesday that talk of curbs was unsubstantiated.

'Shoot itself in the foot'

And Mr Roose signalled that, however disappointing Argentina's harvests may prove, the maths did not stack up for shipment bans.

In corn, for instance, even a harvest of 23m tonnes would sufficient to cover demand, of about 7.5m tonnes, with ease.

"By any stretch, they still have a lot of capacity to export," he said.

Furthermore, the country reaps considerable tax revenue from grain shipments, meaning that for Argentina to ban exports "would be to shoot itself in the foot".

Prices rise

The rumours succeeded in ensuring a positive finish for Chicago crop futures, which had fallen earlier after overnight rains in Argentina proved more generous than had been expecting, so improving prospects, in particular, for soybeans.

Soybeans' later cycle than corn gives them more scope for recovery, should rains persist.

Soybeans for March closed up 0.2% at $12.20 a bushel, while March corn ended 1.9% higher at £163.50 a tonne.

March wheat finished up 2.2% at $6.33 ½ a bushel, with the grain adding 1.9% in Kansas to $6.86 a bushel.

In Europe, which may thanks to geography to be a primary gainer of any Russian export ban, Paris wheat for March closed up 2.1% at a three-week high for a spot contract of E205.75 a tonne.