Abundance and losses of agricultural seeds for waterfowl in Tennessee

Waterfowl acquire high-energy agricultural seeds in harvested and unharvested croplands during migration and winter. Estimates of dry seed mass in agricultural fields are used by biologists and managers to calculate duck-energy days (DEDs) to estimate potential foraging carrying capacity of these fields. However, estimates for corn, grain sorghum and soybean fields do not exist or are outdated for the southeastern United States. Therefore, I estimated seed mass and DEDs in 105 harvested and 59 unharvested corn, grain sorghum and soybean fields across Tennessee, U.S.A., from September--January 2006 and 2007. I also estimated rates of seed loss to germination, decomposition, and depredation and compared seed mass loss between flooded and unflooded fields. Mean seed mass of grain sorghum, corn, and soybean in harvested fields declined 392 to 19, 239 to 39, and 118 to 26 kg ha⁻¹ from post-harvest to January, respectively. Continuous monthly rates of decline were 64% for corn, 84% for soybean, and 74% for grain sorghum. Mean DEDs ha⁻¹ in harvested corn, grain sorghum and soybean fields during January were low (274, 90 and 27), and DEDs were zero in > 85% of fields. In unharvested corn, soybean and grain sorghum fields, mean DEDs ha⁻¹ in January were large (69,000, 18,000 and 26,000), and continuous rates of decline (3%, 7% and 18%) were much lower than for harvested croplands. Scattered corn seed was lost primarily to depredation (37--68%), whereas soybean and grain sorghum seed were lost mostly to decomposition and germination ([greater then equal to]35%).Loss of submersed seed in flooded fields was 40--300% greater than on dry land. I recommend that waterfowl biologists in the southeastern United States should use estimates herein (Table II-3) for DED calculations. I also recommend managers provide unharvested food plots and natural wetlands for waterfowl because seed resources are low in winter in harvested agricultural fields. Given rapid seed loss in harvested and flooded fields, managers should delay harvesting and flooding until immediately prior to the arrival of waterfowl whenever feasible. For agencies interested in modeling fate-based seed loss on a landscape scale, rates of loss in Table III-1 could be used.