Soil Screening

Dr Joschko, you have been researching soil since 1986. Why are you doing this work?

My grand­fa­ther was a farmer, my father a doctor. I combine both profes­sions in my work and inves­ti­gate soil samples with the help of computer tomog­raphy (CT). In the same way that we perform CT scans on people to find out what is wrong with them, it is really quite logical that the best way to analyse soil is to take a good look inside it. The soil struc­ture is extremely impor­tant in agri­cul­tural prac­tice.

What exactly is the soil struc­ture?

Soil struc­ture is the spatial arrange­ment of the solid compo­nents – organic and mineral – and the hollow spaces between them. This varies between different soils and provides indi­ca­tions of fertility and health because quality can be gauged by the grain size, aggre­ga­tion, pore distri­b­u­tion, distri­b­u­tion of plant remains, humus content, rooting, and the diver­sity of soil organ­isms.

The fertility and health of the soil is indi­cated by its struc­ture.

Dr Monika Joschko

How do you look inside the soil?

A team of researchers has been taking soil samples from nine loca­tions in Germany and a further 12 coun­tries in Europe since 2015 for the DIWELA* project.  We then exam­ined the samples with a CT, whereby we virtu­ally cut them into ‘slices’. It was impor­tant that the samples were undis­turbed to ensure reli­able results. In other words, they needed to retain the exact layer and struc­ture as they had under­ground. We used a ‘soil column’ to achieve this in the samples.

That sounds like a lot of work!

But it’s really not. We have even devel­oped a method that enables farmers across Europe to take these field samples. But, of course, we had to make sure that the samples weren’t shaken or disturbed in any other way during delivery. It would have been better if the samples could have been exam­ined directly in the coun­tries.

Do you work together with farmers?

Yes, of course. Our part­ners are farmers. For example, the Komturei Lietzen in Bran­den­burg with 1,100ha. We have been working with them since 1996. At this site, we compare sandy soil with conven­tional, low distur­bance and no-till oper­a­tions at different loca­tions. It’s best to take the sample after harvest, as that is gener­ally when the soil has not been worked for a long time. The find­ings were clear. Under lower tillage oper­a­tions, we found a good crumb struc­ture and numerous earth­worm tunnels, but this was not the case in inverted tillage set-ups. The inves­ti­ga­tions of clay soil in Oder­bruch were also surprising. We took samples from suspected, compacted soil, from driving tracks, and compared them with less-compacted soil from the fields. Despite the loads, the soil struc­ture was fully intact. There can be many reasons for this. In this case it was due to clay soil and many years of min-till using disk harrows.

How can farmers affect the soil struc­ture?

Farmers and growers cannot actu­ally change the grain size and climate in their region. However, they can support the natural processes in the soil. The type of farming plays a major role in soil struc­ture. The selec­tion and sequence of crops and catch crops, as well as the mechan­ical tillage have an influ­ence.

No-till farming is good for the soil struc­ture

Dr. Monika Joschko

No-till farming, for example, provides a good oppor­tu­nity to vary tillage prac­tice, perhaps, working only a third of the soil per season. In the interim period, earth­worms and other organ­isms move around, which is good for soil struc­ture. Farmers can also save costs with no-till farming while achieving the same or even greater yields.

What was the result of the DIWELA* research project?

The results of our analyses can help opti­mise farm manage­ment if farmers take a more focused approach to soil struc­ture. We have created a “struc­ture atlas” of the manage­ment options for different soil types; the results form a good foun­da­tion for further research.

Conclu­sion: The CT sopil struc­ture is a good indi­cator for earth­worm popu­la­tion.

What is your advice for farmers and contrac­tors?

The better farmers know their soil, the more effi­ciently they can farm it. No-till farming, for example, does not prove advan­ta­geous every­where – but it does in some regions. So, for example, sandy soils without a defined soil struc­ture are not suit­able for no-till farming, because they tend towards denser strat­i­fi­ca­tion over the years. 

With heavier soils that can be very dry or wet during seeding, the influ­ence of the tech­nical systems used, fluc­tu­ates heavily, so that yield stability often cannot be achieved. Soils in dry regions often lack mois­ture for active soil organ­isms. It is impor­tant to work soil as little as possible and keep it covered with catch crops or organic matter from the preceding crop. In this way, it can handle heat and heavy rain more easily and soil organ­isms can develop.