PLANTING COVER CROPS (CCS) AFTER A CASH CROP IS HARVESTED IS PROVEN STRATETGY FOR IMPROVING WATER QUALITY AND SOIL HEALTH, AND SUSTAINING THE PRODUCTIVE CAPACITY OF AGRICULTURAL LAND. CONSEQUENTLY, CCS HAVE BECOME IMPORTANT COMPONENTS OF STATE AND REGIONAL SCALE INITIATIVES TO MEET CRITICAL ENVIRONMENTAL CHALLENGES OF LARGE-SCALE AGRICULTURE. IN THE U.S. CORN BELT, WINTER CEREAL RYE IS THE MOST WIDELY USED CCBECAUSE OF ITS SUPERIOR WINTER HARDINESS, GROWTH AT COLD TEMPERATURES, DOCUMENTED ENVIRONMENTAL BENEFITS, AND SUCCESSFUL USE IN CORN-SOYBEAN ROTATIONS. IN SOME YEARS AND FIELDS, HOWEVER, REDUCED CORN YIELDS HAVE BEEN REPORTED FOLLOWING WINTER RYE CCS. AS A RESULT, MANY CORN FARMERS ARE RELUCTANT TO TRY CCS. THIS IS PUZZLING BECAUSE A WINTER RYE CC IMPROVES SOIL HEALTH WHICH SHOULD IN THEORY INCREASE CORN YIELD. MANY POTENTIAL CAUSES FOR THIS YIELD DECLINE HAVE BEEN PROPOSED AND WE PLAN TO INVESTIGATE TWO OF THESE:1. PATHOGENS THAT CAUSE SEEDLING DISEASE IN CORN SURVIVE ON WINTER RYE ROOTS. IF CORN SEED IS PLANTED TOO SOON AFTER THE RYE IS TERMINATED, THE PATHOGENS FROM THE DYING RYE ROOTS ARE ABLE TO INFECT THE GERMINATING CORN SEEDLING. CONSEQUENTLY, WE RECOMMEND PLANTING CORN 10-14 DAYS AFTER THE RYE IS TERMINATED TO ALLOW TIME FOR THE PATHOGEN POPULATION TO DECREASE.2. ACTIVELY GROWING RYE PLANTS UPTAKE NITROGEN (N) AND ALSO IMMOBILIZE N AS THEY DECOMPOSE. WE HAVE A POOR UNDERSTANDING OF HOW REDUCED N AVAILABILITY CONTRIBUTES TO CORN SEEDLING STRESS, SUSCEPTIBILITY TO SEEDLING DISEASE AND REDUCED YIELDS.CCS ARE TERMINATED (KILLED WITH A HERBICIDE) AROUND THE TIME CORN IS PLANTED. NUMEROUS STUDIES HAVE SHOWN IF THE CC IS TERMINATED 10 OR MORE DAYS BEFORE PLANTING CORN, THERE IS LITTLE EFFECT ON THE YIELD OF THE CC. HOWEVER, IN SOME SPRINGS, FREQUENT RAINS DELAY CC TERMINATION AND PLANTING. SOME FARMERS HAVE ASKED IF TERMINATION OF THE CC A FEW DAYS AFTER PLANTING CAN REDUCE YIELD. WE PREDICT THIS PRACTICE MAY REDUCE YIELDS BECAUSE 1. CORN SEED ARE GERMINATING AS THE RYE IS DYING AND, CONSEQUENTLY, SEEDLING PATHOGEN POPULATIONS ARE INCREASING; AND 2. THE RYE PLANTS WILL BE BIGGER, THUS MORE N UPTAKE AND MORE IMMOBILIZATION OF N AFTER CC TERMINATION MAY RESULT IN LESS N AVAILABILE FOR THE GERMINATING CORN SEEDLINGS WHICH MAY INCREASE THEIR SUSCEPTIBILITY TO INFECTION BY SEEDLING PATHOGENS.TO ANSWER THE QUESTION IF TERMINATION OF THE CC A FEW DAYS AFTER PLANTING CAN REDUCE YIELD, WE WILL DO FIELD TRIALS THAT COMPARE TERMINATING THE CC BEFORE PLANTING CORN WITH TERMINATING THE COVER CROP AFTER PLANTING CORN. THESE TRIALS WILL BE DONE AT AN EXPERIMENT STATION AND ALSO ON COMMERCIAL FIELDS. WE WILL MEASURE CORN GROWTH THROUGHOUT THE SEASON, EVALUATE SEEDLING DISEASE, AND COLLECT YIELD DATA. WE WILL SHARE OUR DATA AT VARIOUS EXTENSION EVENTS AND THROUGH SOCIAL MEDIA.THROUGH THIS RESEARCH WE WILL PROVIDE RECOMMENDATIONS TO FARMERS REGARDING TERMINATION OF A CC BEFORE CORN TO REDUCE THE RISK OF REDUCED YIELDS. WE ALSO HOPE TO HAVE AN IMPROVED UNDERS,TANDING OF HOW N UPTAKE AND IMMOBILIZATION BY A CC AFFECTS CORN SEEDLING GROWTH AND DISEASE. WE HOPE THAT WITH IMPROVED RECOMMENDATIONS, MORE FARMERS WILL INCORPORATE CC INTO THEIR PRODUCTION PRACTICES AND THEREBY CONTRIBUTE TO IMPROVED WATER QUALITY AND SOIL HEALTH.