Influence of cropping system on harvest erosion under potato

Cultivation of potato may cause water erosion, wind erosion, tillage erosion and harvest erosion. Little is known about extent and driving forces of harvest erosion, which is the loss of soil by imperfect soil–tuber separation during harvest. We examined the extent of harvest erosion on different scales from plot over field and farm to landscape scale and at different stages of soil–tuber separation from unassisted harvested over assisted harvested, on-farm cleaned, graded to packaged potatoes. On plot scale the influence of cropping practices to lower water erosion was examined with five treatments on three sites over 5 years. On field and farm scale we examined two farming systems (organic versus conventional) on 17 fields covering 5 years. On landscape scale we compared two landscapes over 9 years. Soil losses per harvest were in the same range as can be expected annually for water erosion averaging 8 t ha−1 in plot experiments, 6 t ha−1 on field scale and 2 t ha−1 on landscape scale. The losses decreased drastically with increasing potato processing from 8 t ha−1 with unassisted harvesting to 0.1 t ha−1 for graded and packaged potatoes. Cultivation technique had no influence. This allows applying measures to reduce water erosion without adverse effects on harvest erosion. Farming system exerted a dominant influence on field and farm scale with an average loss on field scale of 8 t ha−1 for conventional and only 3 t ha−1 for organic farming. About half of the variation in harvest erosion on plot and field scale could be described by two planting conditions (rain in March and type of farming) while the remaining variation was caused by harvesting conditions. Harvesting conditions leading to high losses were manifold (e.g. very dry or very wet soil, heavy weed infestation) and could not be described by general relations. On landscape scale planting conditions leveled out and soil and weather conditions during harvest explained 95% of the variation. Losses were higher in years with rainy autumns and in the coarse-loamy landscape because soil shrinkage upon drying improved on-farm soil–tuber separation in the fine-loamy landscape. For highly processed potatoes (graded, packaged) properties of the tuber (specific surface area) exerted a strong influence. Harvest erosion under potato is an underrated process contributing significantly to total soil loss. The extent is lower under organic than conventional farming and can further be largely influenced by on-farm post-harvest processing of the potatoes returning the removed soil to the field where it originated from.