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treatise in the middle of the 12th century. He used Arabic, Greek and Latin sources
and wrote in Arabic.
Ibn al-
'
Aww
â
m
'
s topic offers a very detailed treatment of soils, which is com-
piled in the
rst chapter. The main determinants of quality to him are the capacity of
a soil to warm up and to hold water. Black soils (here color is used in indicator
function) are usually able to absorb heat. Red and yellow soils have a smaller heat
absorbing capacity. White soil is cold and has no af
nity to warmth. But Ibn al-
'
m knows that color can be deceptive, and he gives other qualities as well.
The most desirable texture of a soil is that which looks similar to old and ready-to-
use manure (probably compost), a soil which is not at all compact. Alluvial soil, a
mixture of alluvium and sand, is second to the compost-lookalike in humidity and
freshness (coolness). The coarser a soil, the drier it is, and a soil which is composed
of gravelly sand without any clay or alluvium hence is the driest. Cohesion and
hardness of the clod are main indicators for the dryness of a soil; hardness can reach
that of stone. Soils containing a lot of alluvium are good soils for growing vege-
tables, unless the texture of the soil surface is gummy and viscous.
Experiments to determine soil quality, of which Ibn al-
Aww
â
m offers several,
are best conducted at the onset of winter. Smell and taste, as well as the visual
indicators given above, are the main criteria. Indicator plants, although they
sometimes can be misleading, play an important role, too. The lushness of natural
vegetation indicates water holding capacity, a main criterion for quality. Soil testing
is done by mixing soil with water and tasting the liquid. If it is salty, it can only be
used for palm plantations. Smelling the water can add to the information, as a badly
smelling earth is not fertile. Quoting a writer named Sidagos, Ibn al-
'
Aww
â
m even
presents a parallel experimental setting for the tasting. The most astounding and
unique experiment prescribed by the author is a test aimed at soil biota. A sample of
soil is placed in a tightly sealed clay pot and reburied where it was taken. After
1 week and again after 2 weeks, if the pot is not yet covered with humidity after the
'
Aww
â
rst period, the soil is inspected. If the insects in the pot are black, purple or green,
the soil quality is mediocre. If they are yellow, red or grey, or of a brownish or light
green or white color, the soil is of good quality. The smell of the sample is also
taken into consideration: foul smell indicates bad soil.
Soils were treated elaborately in the Mediterranean, terracing, irrigation, crop
rotation and green manuring were known and practiced. Columella even measures
the quality of a farmer by his ability to procure a given amount of manure from his
stables. 66 The prescriptions on manuring are manifold and comprise not only
organic manures but also mineral soil amendments, in particular, marl. 67 Like
medicine and astrology in Antiquity, agricultural knowledge was rooted in the
system of four humors (humorism). The theory, systematized by Ancient Greek
thinkers around 400 BC, is based on analogies between the four body
uids black
66 Columella ( 1983 ) While this is the best edition and commentary, for quick reference of an
English translation: Columella ( 1941/1948 ).
67 Winiwarter and Blum ( 2008 ).
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