Field Evaluation of Potato N Needs Following Forage Legumes

In an attempt to quantify the nitrogen (N) contribution from forage legumes to succeeding potatoes, trials were conducted on 28 Wisconsin alfalfa or red clover fields. Potato total yield and crop value were determined following in-season fertilizer N applications of 0 to 280 kg ha −1 . Only 2 of the 12 alfalfa sites and 6 of the 16 red clover sites responded to applied fertilizer N when total yield was considered. However, using crop value, responses were seen at 5 alfalfa and 7 red clover sites. Apparent fertilizer replacement value ranged from 0 to 224 kg N ha −1 for both alfalfa and red clover, and averaged 129 or 102 kg N ha −1 for the respective forages. Due to the wide variation, consideration of criteria in addition to preceding crop is necessary to accurately estimate potato N needs following legume forages. Use of the petiole nitrate-N test did not improve the predictive capability.