118 as needed a largely closed loop is maintained However there are also organic farming operations without live stock They then have to source compost for example externally and it becomes more important to add nutrients from elsewhere But then you do not always know exactly where this compost has come from What is it composed of Might it have been contaminated with undesirable substances As a general rule here as well organic farm ing gives particular attention to the soil and its quality Is there less dependence on soil qual ity in conventional farming Yes I don t mean to suggest that the condition of the soil is not considered at all but it plays a much small er role than in organic farming The yield productivity of the crop plants is less dependent on the soil fertili ty development process If soil fertility is lacking e g if root growth is affected by structural damage this can be compensated for in conventional farming by spreading more fertiliser In this kind of farming the soil is more of a medium through which nutrients pass These nutrients extensively sourced externally like in industry are used specifically for plant growth and then exported from the farm in the products sold Lin ear nutrient flows then play a key role The release of nutrients from the soil itself is displaced by the fertil isation Unlike organic farming you can directly add nutrients from the fertiliser bag which the soil does not provide with its own processes to this extent So is there a problem with getting help in the form of a bag of fertiliser Biological and microbiological processes are changed by the addition of readily soluble fertiliser and can come to a complete standstill We are familiar with a similar phenomenon in our own bodies for example if we no longer exercise our muscles or musculoskeletal system our muscle mass declines You have to use it or lose it Humus is a key term in organic farm ing What exactly does it mean In the first instance it is a mix of substances consisting of humic acid and matter which give the fertile topsoil a dark colour However we have to admit that we do not fully know what humus is and how it develops That is why we often avoid the term and use soil organic matter instead This includes as the result of decomposition all dead resi dues from plants animals and micro organisms in their var ious states of decay in and on the soil We use an extremely simplified technique to analyse the soil organic matter We measure the organic carbon in the soil If there is lots of this carbon in the soil then we say there is lots of humus in the soil Grandad s walking stick buried in the ground would be identified as soil organic matter using this carbon analysis method But Grandad s walking stick is clearly not humus Humus in a narrower sense stable humus is a small subset of the soil organic matter that has developed over decades centuries actually made up of many complex organic com pounds enduring for a long time in the soil closely bound to clay minerals In modern terms humus is a fuzzy structure Even though humus plays a crucial role in soil functions sys tem stability and buffering capacities we still cannot unam biguously describe its diverse composition or how it is created But we know there is this spectacular moment when decomposition leads to regeneration Death becomes life And that happens somewhere in this humus This is intensified within the composting process Primary organic matter is broken down by bacteria and fungi in the damp warm environment stable humus matter is gener ated In the field primary organic matter is added to the soil broken down via well understood processes and trans formed by means of processes which are largely not yet un derstood resulting over the long term in the generation of stable humus which is maintained in the soil Humus is the finer formation in the soil and has to do with the human nature of things Education and learning involve the same Continuation of the interview with Prof Ulrich Köpke 6 Nature and people

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