Club of bologna proceedings

Hermann J. Heege
 and 
H. H. Voßhenrich
GERMANY 
The need for soil cultivation mainly results from 
crop or plant successions in modern agriculture. 
In case there is no abrupt crop or plan
succession as with permanent gras
s
land, no one 
thinks about cultivation. And in fact the most
fertile soils in the world have developed under 
permanent grassland or under forests without any 
cultivation. On the other hand, it is well known 
that cultivation can induce serious soil erosion. So 
why do crop successions necessitate cultivation?
Several points are important: 
° 
soil bulk density needed for efficient plant
growth; 
° 
soil aggregate sizes for a high field
emergence; 
° 
weed control; 
° 
crop residue management; 
° 
straw effects in the seedbed. 
1. Soil bulk density 
Removing the crop at harvest time results in an 
increase of soil bulk density due to the harvesting 
machinery and later on due to rain. The farmers 
try to compensate for this by cultivaion. They 
have to consider the long term climatic cond itions 
(
Fig. 1
). In humid areas the water supply of the 
crop se ldom is a problem, but the soil aeration 
often is. Therefore the farers have to cultivate 
rather deeply and thoroughly and for this
traditionally use the moldboar
d-
plow as pr
i
mary 
tool. For 
ar
id areas instead of the soil aeration 
the water supply is the problem; consequently
cultivation is either very sha
l
low or left out
completely. And of cause it is not the climate 
alone which should determine the amount of
cultivation. In some soils the tex
t
ure and the
organic matter content pr
o
vide for suffi
c
ient 
aeration. Thus concerning the bulk density these 
soils can produce well even in a humid climate 
with little or no cul
t
ivation. Additional factors in 
this respect are the crop rota
t
ion and especi
a
lly 
the time span between harvest and establishment 
of the next crop.
The farmers can adopt to the long term cl
i
mate; 
yet it is almost impossible for them up to now to 
react adaequately to the short term weather
variations. Ideally they would have to pro
v
ide for 
a high bulk density in a dry season and vice versa 
in a wet year (
Fig. 2
). Despite the fact that many 
weather satellites now operate combined with
modern computers, the weather forecasts still are 
not rel
i
able beyond a few days. Much better
adapted cultivation could be realized if in the
future the forecasts can be accurate for some 
weeks.