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Trends and deviations in the yield of the english wheat crop during the last 750 years


, : Trends and deviations in the yield of the english wheat crop during the last 750 years. Agro Ecosystems 3(1): 1-10

The yield of wheat in England has increased more than 6-fold during the last 750 yr, from 0.5 tonne/ha in the 1st half of the 13th century to 3.4 tonne/ha in the 3rd quarter of the 20th century. Present yields are nearly 4.5 tonne/ha per yr representing a 9-fold increase from beginning to end of the period. Over this period the trend is best represented by a parabolic equation relating the logarithm of yield to year, which accounts for some 95% of the yield variation with time. Deviations of individual yearly yield from the long term trend are represented by a sample SE of 0.25 tonne/ha. More than three quarters of the increase has occurred in the last 300 yr when yields rose almost exponentially, doubling every 150 yr. However, most of the increase was in 2 comparatively short periods, 1820-1860 and post-Second World War. In the last 30 yr the national wheat yield has increased at 0.079 tonne/ha per yr, twice as fast as in the accelerating phase of the previous century. Data on the short-term annual deviations from the long-term trends indicate that they are approximately proportional to the general yield level. After removing the long-term trend, the coefficient of variation is some 7% of the mean national yield.

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Accession: 006839280

DOI: 10.1016/0304-3746(76)90096-2

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