Technological advances in soil preparation and seed placement at planting time, use of crop rotation and fertilizers to improve plant growth, and advances in harvesting methods have all combined to promote wheat as a viable crop. Agricultural cultivation using horse coller leveraged plows was one of the first innovations that increased productivity. Much later, when the use of seed drills replaced broadcasting sowing of seed in the 18th century, another great increase in productivity occurred. Yields of wheat per unit area increased as methods of crop rotation were applied to long cultivated land, and the use of fertilizer became widespread. Improved agricultural husbandry has more recently included threshing machines and reaping machines, tractor-drawn cultivators and planters, and better varieties . Great expansions of wheat production occurred as new arable land was farmed in the Americas and Australia in the 19th and 20th centuries.