Árbók Hins íslenzka fornleifafélags - 01.01.2004, Blaðsíða 107

All four alleged ancient barley fields studied are positively man made features. The
fields at Akurey and Hólavellir were impossible to date as none of the tephra layers found
in off-site sections were observed in the trial trenches. The Ketilsstaðir and Fagridalur
sites produced, however, ample tephra deposits for dating the different soil layers and
activities. Pollen grains of Hordeum type were found at all sites except at Fagridalur.
Although disturbance of the different soil layers at the four sites studied can be explained
as the result of agricultural activities, conclusive confirmation for barley cultivation was
not obtained. However, interpretation of evidence acquired at Ketilsstaðir strongly
suggests that the terraced field had been used for cultivation of barley.The sections in the
trial trench at Ketilsstaðir show that long before the tephra H-1341 (deposited AD 1341)
fell, the soils had been disturbed and thus mixing the Landnam tephra (AD 871±2) and
the tephra layer from 934 into the soil. When the volcano Katla erupted in 1357 the
tephra fell on a surface that had been or was still in the process of being tilled.
Micromorphological and soil chemical analyses show that manuring occurred, using
domestic waste, fuel residue material and possibly animal manures, but that application
rates were at low levels, indicating that production was only at subsistence level. The
effect of reduced manuring levels post 1357 AD at Ketilsstaðir and the observed impact
on soil organic matter carbon and nitrogen levels and on crop yields provides further
strong evidence that soil nutrient availability - particularly nitrogen - was a major
limiting factor on grain yield. The integrated modelling of soils, climate and land
management data has also permitted an assessment of the relative significance of climate
and soils in restricting grain production in Iceland.These analyses indicate that climate is
less significant as a limiting factor than previously thought and that subsistence cereal
production could have continued beyond the climatic deterioration of the 1400s. Instead
of climate, soils and the management of soils, emerge as a critical limiting factor to early
grain production.
106 ÁRBÓK FORNLEIFAFÉLAGSINS