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Straw and minimal disturbance are good for the soil

Conservation agriculture is gaining ground worldwide. New Danish experiments have been quantifying its effect under Danish conditions and show, among other things, a positive effect of leaving the straw on the ground in a reduced tillage systems.

[Translate to English:] Efterladelse af halmen på marken bidrager positivt til jordens struktur og dermed dens frugtbarhed. Foto: Janne Hansen

Conservation agriculture is strongly recommended by FAO as a sustainable approach to crop production. But what exactly is it and what is the effect under Danish conditions? This is explained by Senior Scientist Lars J. Munkholm from the Department of Agroecology at Aarhus University.


There are three central elements to conservation agriculture:


  • Minimal soil preparation
  • Permanent soil cover from, for example, plant residues and catch crops
  • Diverse crop rotations


- An optimal soil structure for crop production is essential in conservation agriculture. The concept is the subject of much interest in Europe and Denmark – particularly with farmers interested in no-till farming, explains Lars J. Munkholm. He has studied the effects of conservation agriculture for a number of years.


His research team found, among other things, that abandoning the straw on the field had a significant impact on soil structure where the structure of the soil to 27 cm depth was improved by leaving the straw on the surface – regardless of the tillage method.


- This is especially important with reduced tillage where compaction under the tilled layer can often be a problem, says Lars. J. Munkholm.


Straw improves the soil structure

Although some practical experience with conservation agriculture has been gained, scientific studies are relatively scarce. Since the study of such a management system it fairly complex, few studies have quantified the impact of conservation tillage in combination with diversified crop rotations and permanent soil cover. It also takes time to study the long-term effects of this management concept.


Reduced tillage will on its own improve the structure of the topsoil (0-5 cm), but often results in compaction problems below tillage depth.


- The question is whether other elements of conservation agriculture can alleviate the compaction problem by stimulating the biological activity of the soil, says Lars J. Munkholm. New results show that to some extent they can.


In a long-term study they investigated the effect of crop rotation, straw management and soil tillage on different parameters in the soil. The crop rotations varied from a crop rotation with winter crops to a more diversified crop rotation with both spring and winter crops and catch crops. For the latter, the straw was removed in some plots and in others it was left on the ground. The tillage systems ranged from direct seeding with tine coulters over reduced tillage with harrowing to ploughing to 8-10 cm depth.


After 11 years of experimenting, the scientists found that retaining the straw improved the soil structure irrespective of tillage method, whereas there was no obvious effect of crop rotation.


For further information please contact: Senior Scientist Lars J. Munkholm, Department of Agroecology, telephone: +45 8715 7727, mobile: +45 2515 2716, email: lars.munkholm@agro.au.dk