deterioration in their
quality. The quantity of fodder was decreasing for this reason, almost
imperceptibly, but none the less seriously. Fewer cattle could be kept
as the grass land deteriorated, and the small quantity of manure which
was available for restoring the productivity of the open fields was
gradually decreasing for this reason.

Soil exhaustion went on during the Middle Ages not because the
cultivators were careless or ignorant of the fact that manure is
needed to maintain fertility, but because this means of improving the
soil was not within their reach. They used what manure they had and
marled the soil when they had the time and could afford it, but, as
the centuries passed, the virgin richness of the soil was exhausted
and crops diminished.

The only crops which are a matter of statistical record are those
raised on the demesne land of those manors managed for their owners by
bailiffs who made reports of the number of acres sown and the size of
the harvest. These crops were probably greater than those reaped from
average land, as it is reasonable to suppose that the demesne land was
superior to that held by villains in the first place, and as it
received better care, having the benefit of the sheep fold and of such
stall manure as could be collected. Even if it were possible to form
an accurate estimate of the average yield of demesne land, then, we
should have an over-estimate for the average yield of ordinary
common-field land. No accurate estimate of the average yield even of
demesne land can be made, however, on the basis of the few entries
regarding the yield of land which have been printed. Variations in
yield from season to season and from manor to manor in the same season
are so great that nothing can be inferred as to the general average in
any one season, nor as to the comparative productivity in different
periods, from the materials at hand. For instance, at Downton, one of
the Winchester manors, the average yield of wheat between 1346 and
1353 was 6.5 bushels per acre, but this average includes a yield of
3.5 bushels in 1347 and one of 14 bushels in 1352,[43] showing that no
single year gives a fair indication of the average yield of the
period. For the most part the data available apply to areas too small
and to periods too brief to give more than the general impression that
the yield of land was very low.

In the thirteenth century Walter of Henley and the writer of the
anonymous _Husba