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Nitrogen Availability in an Organic Potato Crop Following 3-Year Transition under Contrasting Farming Systems

Organic farming systems often involve livestock and/or forages. However, managing soil nitrogen (N) availability by adjusting soil amendment rates and forage duration in crop rotations is a challenge. A 4-year experiment was conducted to evaluate N availability in the fourth year of organic potato systems with contrasting livestock and forage components. The experiment included three forage levels (0, 1, or 2 years of forage) through 4-year rotations starting with wheat (Triticum aestivum L.) and ending in potato (Solanum tuberosum L.). Within each forage level, three soil amendments (alfalfa meal, composted beef manure, and composted poultry manure) represented nutrient sources from stockless, ruminant, and monogastric systems, respectively. As farmers do, we modified the amendment application rate and timing by taking a system approach to reflect crop rotations. Nitrogen availability was higher in alfalfa meal compared with the composts varied with feedstocks. Nitrogen supply from soil amendments differed in the year of application, with no apparent N carryover effects. With increased forage frequency, soil N supply rates increased in the organic potato season following the 3-year transition period. The pre-experimental pasture with high soil fertility limited differences in plant N uptake among treatments. Nitrogen availability as indicated by potato N uptake was linearly related to cumulative amendment inputs in spite of different amounts of amendment input to different treatments.