ndry_ are authorities for the opinion that the average
yield of wheat land should be about ten bushels per acre.[44] At
Combe, Oxfordshire, about the middle of the century, the average yield
during several seasons was only 5 bushels.[45] About 1300, the fifty
acres of demesne planted with wheat at Forncett yielded about
five-fold or 10 bushels an acre (five seasons).[46] Between 1330 and
1340, the average yield (500 acres for three seasons), at ten manors
of the Merton College estates was also 10 bushels.[47] At Hawsted,
where about 60 acres annually were sown with wheat, the average yield
for three seasons at the end of the fourteenth century was a little
more than 7-1/2 bushels an acre.[48]

Statistical data so scattered as this cannot be used as the basis of
an inquiry into the rate of soil exhaustion. Where the normal
variation from place to place and from season to season is as great as
it is in agriculture, the material from which averages are constructed
must be unusually extensive. So far as I know, no material in this
field entirely satisfactory for statistical purposes is accessible at
the present time. There is, however, one manor, Witney, for which
important data for as many as eighteen seasons between 1200 and 1400
have been printed. A second suggestive source of information is Gras's
table of harvest statistics for the whole Winchester group of manors,
covering three different seasons, separated from each other by
intervals of about a century. The acreage reported for the Winchester
manors is so extensive that the average yield of the group can be
fairly taken to be the average for all of that part of England.
Moreover, Witney seems to be representative of the Winchester group,
if the fact that the yield at Witney is close to the group average in
the years when this is known can be relied upon as an indication of
its representativeness in the years when the group average is not
known. The average yield for all the manors in 1208-1209 was 4-1/3
bushels per acre; for Witney alone, 3-2/3. In 1396-1397 the yield of
the group and the yield at Witney are, respectively, 6 and 6-1/4
bushels per acre.[49]

Table III shows the yield of wheat on the manors of the Bishopric of
Winchester in the years 1209, 1300 and 1397. If it could be shown that
these were representative years, we should have a means of measuring
the increase or decrease in productivity in these two centuries. Some
indication of the representativen