section_path: Science and technology/Metallurgy and agriculture
section_name: Metallurgy and agriculture
paragraph_text: Metallurgy and agriculture
  
  Evidence suggests that blast furnaces, that convert raw iron ore into pig iron, which can be remelted in a cupola furnace to produce cast iron by means of a cold blast and hot blast, were operational in China by the late Spring and Autumn period (722–481 BC). The bloomery was non-existent in ancient China; however, the Han-era Chinese produced wrought iron by injecting excess oxygen into a furnace and causing decarburisation. Cast iron and pig iron could be converted into wrought iron and steel using a fining process.
  
  The Han dynasty Chinese used bronze and iron to make a range of weapons, culinary tools, carpenters' tools, and domestic wares. A significant product of these improved iron-smelting techniques was the manufacture of new agricultural tools. The three-legged iron seed drill, invented by the 2nd century BC, enabled farmers to carefully plant crops in rows instead of sowing seeds by hand. The heavy mouldboard iron plough, also invented during the Han, required only one man to control it with two oxen to pull it. It had three ploughshares, a seed box for the drills, a tool which turned down the soil and could sow roughly 45,730 m (492,200 sq ft) of land in a single day.
  
  To protect crops from wind and drought, the grain intendant Zhao Guo (趙過) created the alternating fields system (daitianfa 代田法) during Emperor Wu's reign. This system switched the positions of furrows and ridges between growing seasons. Once experiments with this system yielded successful results, the government officially sponsored it and encouraged peasants to use it. Han farmers also used the pit field system (aotian 凹田) for growing crops, which involved heavily fertilized pits that did not require ploughs or oxen and could be placed on sloping terrain. In the southern and small parts of central Han-era China, paddy fields were chiefly used to grow rice, while farmers along the Huai River used transplantation methods of rice production.