Organic potatoes, reduced tillage and mulch in temperate climates

Summary

The experiments with mulching were done in a systems approach comparing potatoes as they are typically produced in Germany with ploughing to a system of non-inversion tillage combined with mulch. As the plots are integrated in two long-term experiments comparing ploughed versus minimum tillage it was not possible to integrate a mulched ploughed treatment or a non-mulched non-inversion tillage due to restrictions in plot size. We tested the effects of mulching in a ploughed system in 2015. There was no late blight but good erosion control (Pict.5) and yields were increased through mulching. Compost effects on the system were so far not clearly visible. It will most likely take several more years of regular applications to start seeing changes in system performance.
Overall, mulching will change the potato system and it will depend very much on the local soil and climatic conditions if and when mulching will be positive (Table 1). On the one hand, mulching is labor intensive and requires the availability of materials to use. Besides freshly cut materials silage is an alternative option some farmers are using in vegetables in Germany. This reduces the dependence on the growing conditions for the mulch early in the season and likely also increases the fertilization effect. Farms that have no animals often mulch grass-clover. This will suppress N-fixation by the clover due to the nutrients in the mulch and thus reduce the usefulness of the grass-clover for nutrient accumulation. In addition it may result in leaching and thus loss of nutrients and even potentially harm the environment. Using the first and most rich harvest as mulch in the potatoes or alternatively making silage for later use is easier than composting such materials. Once the mulch is applied, no more mechanical weed control is done saving labor and energy. More importantly, it will also reduce the mechanical damage done to the potato foliage that makes them more susceptible to infections and it allows for profuse growth of fine roots into the applied mulch materials. Mulching also reduced Colorado potato beetles in both years to some extent but these data need confirmation. Also, the residual effects on the subsequent crop after the potatoes due to the increased input of organic amendments still need to be studied.
Ecologically speaking mulching has many advantages. These advantages are especially important in water restricted areas. If and how mulching is feasible and economical depends on the specific conditions and organization of a farm, however.