World grain prices soared last year, boosting turnover for the 1 500 farmers at the Agropal co-operative led by Ferreras in the grain belt in the northern region of Castilla-Leon.
Beating a winter drought by planting more grain in the last northern winter, Spanish farmers were expected by the agriculture ministry to harvest 23.75 million tons this year, virtually level with last year.
But key US markets recently peaked and Ferreras says the commodities boom has brought him costlier fuel and fertilisers, rather than lasting poverty. Some farmers are already thinking of switching away from grain this winter.
While American demand for biofuel crops has been a factor underpinning grain prices, Spain's fledgling industry accounts for a very small percentage of demand for grain, offering scant structural support for farmers like Ferreras.
"Last year was a one-off. We were just able to pay off our debts for once and invest in a bit more machinery," said Ferreras.
He is particularly concerned that an imminent flood of imports from the Black Sea to fill Spain's structural grain deficit will only exacerbate the downward trend in prices.
Europe faces a big grain crop this summer that has taken the shine off record high markets, although recent heavy rain has dented quality in some areas.
This has particularly been the case in Black Sea regions, where much of the grain will be suitable only for animal feed.
Last year's high prices helped boost Agropal's turnover by 29 percent to about e120 million (R1.4 billion) in the year to June. But Ferreras estimates that production costs have since risen by 60 percent.
Martin Aliste, Ferreras' crop manager, said: "We're having our best harvest in years, but have barely time to savour it. Rising costs make it a bittersweet moment."
The agriculture ministry said in its latest crop progress report that the main reason Spain would have a bumper crop this year, after a severe drought in winter, was that farmers planted almost 9 percent more land.
However, Jesus Maria Fernandez, a broker at grain firm Zeleny, has already forecast that farmers will sow less grain this winter due to rising costs. "It's cheaper now for farmers to grow sunflowers, and that is bad news for food supply in Spain," he said.
Even in a good year, Spain typically imports about 12 million tons of grain, which cost e3 billion last year, as its soil is less productive than in northern and eastern Europe.
Port sources have said that 250 000 tons of feed wheat were due to arrive this month alone, in the northeastern port of Tarragona, from Bulgaria, Romania and Ukraine.
Ukraine expects its grain harvest this year will soar to 43 million tons from 29.3 million last year. It expects to export 17.5 million tons in 2008/09.
"These shipments are helping to sink wheat prices a bit more," said a report from the Mercolleida grain exchange. "The big question everyone is asking is how far prices can fall."
Feed wheat for forward delivery in Tarragona has tumbled to about e182 a ton, from e265 in March, which has in turn forced down prices for domestic grain.
Europe's biofuel industry has added extra demand for grains that are used for ethanol and for oilseeds that are used for biodiesel. But these industries have been hit by rising feedstock costs and in some countries by cheaper ethanol imports.
In Castilla-Leon, Spain's largest bioethanol plant has been idle since September, as high grain prices hit domestic demand for grain-based fuel. There are plans to restart the plant in the hope that a new domestic law that requires petrol to contain a minimum percentage of biofuel will revive demand.