Club of bologna proceedings

particles tend to absorb chemica
l
s. Farmers
know, that the effect of soil acting herbicides
depends very much on the 
a 
bsorption by the 
organic matter of the soil. It is possible, that
degradation products from the straw are
absorbed in a similar way. In short, experiments 
with watery ext racts on germination paper do not 
explain, what happens to the emergence in soils. 
Figur
e 8
shows, how straw affected the
emergence of rape in pure sand in the lab oratory. 
The results are surprising. Since hardly any
absorption of chemicals can be expecte
d
in pure 
sand, especially harmful toxic effects of straw on 
the emer gence might be expected. But just the 
opposite effect occured. The lowest emergence 
was recorded when no straw was added to the 
seedbed. By far the best emergence was
achieved when straw was incorporated or mixed 
into the seedbed. Placing the straw on the top of 
the seedbed was much inferior to incorporating it, 
however, still better than no straw at all.
These results are completely contradictory to the 
assumption, that straw in the seed
b
ed impedes 
the emergence. The same experiments were done 
with fresh straw and with straw, which was
subjected to extraction by water. It was assumed 
that the difference between the two types of
straw would show, whether watery extracts from 
the straw are 
s
till harmful on emergence in the 
soil. Since no significant absorption of the harmful 
chemicals should be expected in pure sand, it is 
remarkable that the emergence curves with both 
straw treatments are almost identical. These
results do not at all indica te that straw as a whole 
or watery extracts from it are harmful to the
emergence of rape, the results demonstrate the 
opposite. However, pure sand presents certainly 
conditions which differ from those in natural soils.