Club of bologna proceedings

Karl Th. RENIUS 
Germany 
I would like to provide some better guidelines 
for developing countries. I remember there 
was a publication, 40 years ago, with 
diagrams which, taking as inputs the soil type, 
initial bulk density, moisture content and 
normal pressure on the soil, give the porosity 
as an output. And there is a lot of information 
on the critical porosity, which is between 42% 
and 46-48%, so if you get this information out 
of these diagrams, you have a first guideline. I 
wonder that these diagrams are not more 
used, perhaps many people have already 
forgotten about them, but the quality is very 
good. 
 
Jaime ORTIZ-CAÑAVATE 
Spain 
First, just a small point about the excellent 
paper by Prof. Heege - I think in figure 4 the 
units should be revolutions per minute, rather 
than hertz per minute. I also want to make a 
comment about the gantry. We have been 
hearing about the gantry tractor for a long 
time, the first on these types of tractors dates 
back maybe 20 years and - well - everyone 
likes the idea, I think it’s a very bright idea, 
but my question is: is that real? Can it be 
used by real farmers? How many gantry 
tractors are sold commercially? From my 
point of view, compaction is very important 
subject, and there are maybe other 
approaches that I would like to comment, like 
the rubber-track tractors which have been 
developed by Caterpillar and John Deere. 
They are very good for the soil. I like the idea 
of gantry tractors, but my opinion is that the 
real farmer is not able to use this bright idea. 
 
Tim CHAMEN
I understand they’ve been around for a long 
time, in fact since 1855. But recently they’ve 
not really had a major input from a big 

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manufacturer. And that’s, I think, the key to 
developing the engineering to make them 
truly practical, flexible and farmer-friendly. 
I’m still hopeful that that’s going to happen in 
the next few years, that we will see a 
significant input of money to develop them 
properly, for the market. I think they will be 
there alongside other systems. Track systems, 
as Ortiz Canavate says, are developing day by 
day, and we are seeing much larger 
introduction of these type of systems now... 
Can I just lead on from that to the question 
raised by Prof. Singh, regarding best practice 
advice for compaction. Probably you are not 
aware, most of you, but there is a European 
Union concerted action taking place at the 
moment on subsoil compaction, looking at 
how many soils are vulnerable, if they are 
vulnerable how much damage they are 
sustaining, and what to do about it. And part 
of our remit within that concerted action 
group is to come up with best practice advice 
for farmers, to address the problems that are 
likely to be associated with subsoil 
compaction.