The Tsar should have been so grateful that he might just give away Alaska...
Russia was the only real competitor that the United States had for the title of breadbasket of Europe. Grain from Poland, Ukraine and Belorussia would make up some of the shortfall. Prices would rise with the scarcity of grain, allowing Russian landowners to significantly increase their incomes.
This would coincide with the emancipation of the serfs (an event which freed quite a few more souls than the 13th Amendment would a few years later). A few years of extra-profitability would have been beneficial to the newly freed peasants, as it would have allowed them to pay off their redemption payments to the government. Those peasants not part of the Mir collectives would be better positioned to enter the emerging capitalist economy.
Of course once he US Civil War ended, Midwestern farmers would flood the market with grain, causing prices to decline. If the price decline was precipitous enough, it would probably ruin many Russian and European farmers who took on debt to increase their production during good times.
I cannot comment on the rest of Europe, but I wonder how such an event would effect politics in the UK. The Corn Laws had been repealed only in 1849. A great deal of land had been taken out of production after the decline in grain prices. A sudden increase in the price of corn (grain), combined with the cotton embargo would have caused a worse recession than the UK suffered OTL.
Perhaps, as a result, the next Tory government would have been less eager to embrace Free Trade, and imposed a tariff on grain as a hedge against future grain embargoes?