By Maximilian Heath BUENOS AIRES (Reuters) - Farmers in Argentina staged a protest in Santa Fe province on Tuesday to demand lower taxes and a better exchange rate for their exports, amid a prolonged economic slump and historic drought that has battered crops and agricultural output. Farmers are asking President Alberto Fernandez s government for less burdensome interventionist trade policies and the elimination of export taxes, as they suffer from the worst drought in 60 years. We ve been warning that the situation for farmers is difficult with drought, with frost, said Carlos Achetoni, president of farm federation FAA, in a video announcing the demonstration posted on Twitter. Argentina s capital controls have propelled popular informal currency markets where U.S. dollars are twice as expensive as the official, tightly controlled rate. The controls create a disincentive for farmers to export since revenues in dollars have to be converted back to the local peso currency at the lower o