Biological and mechanical subsoiling in potato production – a participatory research approach

Soil compaction in agricultural fields has increased due to the use of heavy agricultural machinery and intensified vehicular traffic. Compaction reduces total porosity, permeability and water-holding capacity in soil, leading to poorer aeration and impeded root development and nutrient uptake. Soil compaction occurs in topsoil and subsoil, but subsoil compaction is considered more persistent, complex and costly to alleviate. Mechanical methods such as deep tillage and biological methods such as use of deep-rooting crops are available to deal with soil compaction, but combining these methods might tackle compaction more efficiently. This thesis investigates the effects of mechanical inter-row subsoiling, biological subsoiling and a combination of these on soil penetration resistance, potato root length density, nutrient uptake, tuber yield and quality. Part of the study involved interdisciplinary methodology and participatory research, in which farmers, advisors and researchers formed a collaborative research group to develop effective methods to reverse soil compaction and improve potato production. To test hypotheses field experiments at an experimental farm and on seven collaborating farms in southern Sweden (Skåne, Blekinge and Östergötland) following the principle for the so called mother and baby (farm) trial design were performed. Inter-row subsoiling alone and in combination with preceding crops greatly improved soil penetration resistance. Root length density (RDL) was higher in the combined treatment than in the separate inter-row and biological subsoiling treatments. Nitrogen uptake increased with inter-row subsoiling which in starch potato trials could be shown as an increase in total tuber yield. A positive effect of autumn-sown oilseed radish as preceding crop treatment was shown in farm trials. The incidence of external and internal quality defects was low in all treatments. The results from the field trials led to many interesting debates with participating farmers with specific knowledge of their own farm conditions and to a new, deeper understanding of the potato cropping system and potential improvements. Over time, the unique combination of a collaborative research group in connection with regional participatory learning and development groups became a combined boundary organisation. Such structures can close the gap between science and practical farming and contribute to innovation and capacity building among farmers and all stakeholders, and thus need to be created and maintained.