Editing Wheat (section)

===Late 20th century yields===
In the 20th century, global wheat output expanded by about 5-fold, but until about 1955 most of this reflected increases in wheat crop area, with lesser (about 20%) increases in crop yields per unit area. After 1955 however, there was a ten-fold increase in the rate of wheat yield improvement per year, and this became the major factor allowing global wheat production to increase. Thus technological innovation and scientific crop management with [[Haber process|synthetic nitrogen fertilizer]], irrigation and wheat breeding were the main drivers of wheat output growth in the second half of the century. There were some significant decreases in wheat crop area, for instance in North America.<ref>{{cite book |last1=Slafer |first1=G.A. |last2=Satorre |first2=E.H. |chapter=Chapter 1 |year=1999 |title=Wheat: Ecology and Physiology of Yield Determination |publisher=Haworth Press |isbn=1-56022-874-1}}</ref> Better seed storage and germination ability (and hence a smaller requirement to retain harvested crop for next year's seed) is another 20th-century technological innovation. In medieval England, farmers saved one-quarter of their wheat harvest as seed for the next crop, leaving only three-quarters for food and feed consumption. By 1999, the global average seed use of wheat was about 6% of output.<ref>{{cite book |last1=Wright |first1=B. D. |last2=Pardey |first2=P. G. |chapter=Agricultural R&D, productivity, and global food prospects |title=Plants, Genes and Crop Biotechnology |year=2002 |pages=22-51<!--p. 26--> |publisher=Jones & Bartlett Learning |isbn=9780763715861 |chapter-url=https://books.google.com/books?id=UF94McWtLP0C&pg=PA22}}</ref>
In the 21st century, rising temperatures associated with [[global warming]] are reducing wheat yield in several locations.<ref>{{Cite journal |last1=Asseng |first1=S. |last2=Ewert |first2=F. |last3=Martre |first3=P. |last4=Rötter |first4=R. P.|last5=Lobell |first5=D. B. |last6=Cammarano |first6=D. |last7=Kimball |first7=B. A. |last8=Ottman |first8=M. J. |last9=Wall |first9=G. W. |last10=White |first10=J. W. |last11=Reynolds |first11=M. P. |display-authors=5 |date=2015 |title=Rising temperatures reduce global wheat production |journal=[[Nature Climate Change]] |volume=5 |issue=2 |pages=143–147 |doi=10.1038/nclimate2470 |bibcode=2015NatCC...5..143A |url=http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://eprints.whiterose.ac.uk/85540/1/Main_Asseng_2014-9-22.pdf |archive-date=2022-10-09 |url-status=live}}</ref>