<onlyinclude> Agriculture involves the domestication of plants. Data from molecular and archaeological research generated over the past 15 years now makes it clear that agriculture began independently over a much larger area of the globe than was once thought, and included a diverse range of taxa. At least 11 regions of the Old and New World were involved as independent centers of origin, encompassing geographically isolated regions on most continents, but several more have been suggested. The earliest development was around 11,500 years ago separately in both the Fertile crescent and at Chogha Golan in modern day Iran, where wild barley, wheat and lentils were cultivated and where domesticated forms of wheat appeared about 9,800 years ago. The Fertile Crescent of Western Asia, Egypt and the Indus Valley were sites of the earliest planned sowing and harvesting of crops which had previously been gathered in the wild. Independent development of agriculture occurred in northern and southern China, Africa's Sahel, New Guinea, parts of India and several regions of the Americas. Agricultural techniques such as irrigation, crop rotation, and application of fertilizers were developed soon after the Neolithic Revolution but have made significant strides in the past 200 years. The Haber-Bosch method for synthesizing ammonium nitrate fertilizer represented a major breakthrough and allowed crop yields to overcome previous constraints.