Ethnicity made a difference in agricultural practice. As an example, German farmers generally preferred oxen rather than horses to pull their plows and Scots-Irish made a farming economy based on hogs and corn. Eventually cows were brought with the horses. They were more useful than horses for many reasons. Almost all the farms had cows on their land. In Ireland, people farmed intensively, working small pieces of land trying to get the largest possible production-rate from their crops. In the American colonies, settlers from northern Ireland focused on mixed-farming. Using this technique, they grew corn for human consumption and as feed for hogs and other livestock. Many improvement-minded farmers of all different backgrounds began using new agricultural practices to raise their output. During the 1750s, these agricultural innovators replaced the hand sickles and scythes used to harvest hay, wheat, and barley with the cradle scythe, a tool with wooden fingers that arranged the stalks of grain for easy collection. This tool was able to triple the amount of work done by farmers in one day. Farmers also began fertilizing their fields with dung and lime and rotating their crops to keep the soil fertile. By 1700, Philadelphia was exporting 350,000 bushels of wheat and 18,000 tons of flour annually. The Southern colonies in particular relied on cash crops such as tobacco and cotton. South Carolina produced rice and indigo. North Carolina was somewhat less involved in the plantation economy, but because a major producer of naval stores. Virginia and Maryland came to be almost totally dependent on tobacco, which would ultimately prove fatal at the end of the 18th century thanks to exhausted soil and collapsing prices, but for most of the century, the soil remained good and a single-crop economy profitable.