Saving Rice for Ducks & Dollars for Farmers

Richard M. Kaminski, Jennifer Kross, Joshua D. Sta,

Although combines are becom-ing increasingly efficient for harvesting rice, some grain inevitably escapes and falls to the ground during harvest. This "waste rice" is important food for migrating and wintering ducks and geese, but recent research by wildlife scientists at Mississippi State University (MSU) reveals the abundance of waste rice at harvest now declines an average of about 70% by late fall-early winter. Dr. Rick Kaminski, MSU project leader and wildlife professor, said, "Nowadays, varieties of rice are planted in early spring and harvested between late summer-early fall, resulting in losses of waste rice to germination, decomposition, and consumption by insects, birds, and rodents during fall before ducks and geese arrive to winter in the Lower Mississippi Alluvial Valley (MAV)." Late-fall abundance of waste rice is about 60% less now than a previous estimate from the 1980s used by the U.S. Fish and Wildlife Service and other waterfowl conservation partners in efforts to estimate the carrying capacity of the MAV for wintering waterfowl. The MSU researchers speculate significant reductions in waste agricultural seeds (particularly rice and soybean) may be linked to the current decreased abundance of mallard ducks wintering in the MAV.

To address the issue of waning waste rice, the researchers have been evaluating ways to conserve the lost grain after harvest for wintering waterfowl. As part of Joshua Stafford's doctoral research, he sampled over 150 harvested rice fields throughout the MAV of Arkansas, Louisiana, Mississippi, and Missouri during autumns 2000-2002. Each time Dr. Stafford sampled a harvested rice field, he recorded whether rice stubble in the field was burned, disked, rolled, or left standing. Stafford did not detect any statistical differences in average abundance of waste rice in late fall among post-harvest fields treatments. Nevertheless, average abundance of waste rice in fields with standing stubble (110 lbs/acre [dry weight]) was about 2 times greater than the combined average for fields burned, disked, or rolled (62 lbs/acre).

Extending upon Stafford's research, Jennifer Kross, a current MSU graduate student completing her Master's degree in wildlife science, conducted experiments in 19 rice production fields around Arkansas and Mississippi during falls 2003 and 2004. She estimated the amount of waste rice persisting until late fall in field paddies where stubble was burned, disked, mowed, rolled, or left standing after harvest.

Consistent with Stafford's results, Kross found significantly more waste rice, on average, in standing stubble (93 lbs/acre) than the combined average for other post-harvest treatments (52 lbs/acre). In descending order, average abundance of waste rice was 65 lbs/acre, 60 lbs/acre, 45 lbs/acre, and 43 lbs/acre in burned, mowed, rolled, and disked paddies, respectively. Only standing-stubble, burned, and mowed paddies contained average abundances of waste rice at or exceeding 45 lbs/acre, which previous research in Arkansas demonstrated was a threshold for rice-field feeding by mallard ducks. Below this threshold, mallards "give-up" feeding and abandon rice fields.

The scientists are contemplating explanations for the greater abundance of waste rice in standing than manipulated stubble. Kaminski recommended "staying tuned" for final results and explanations in Kross's thesis which is scheduled for completion in fall 2005.

Meanwhile, if you are a rice producer in the MAV and desire to manage your fields after harvest for wintering waterfowl, the scientists' preliminary recommendation is to leave stubble standing in harvested fields or attempt an incomplete burn across fields to produce "patches" of burned and unburned stubble. Variation in moisture content of rice straw and soil within rice fields may create a patchwork of burned and unburned stubble. When rice fields are subsequently flooded, the burned areas should become open-water landing and foraging areas for waterfowl.
Interestingly, Houston Havens, another current MSU Master's student working on the Monsanto Farm and Wildlife Management Center near Stuttgart, Arkansas, recorded the greatest abundance of mallards and other waterfowl using burned paddies during winter 2004-2005. Additionally, Havens found that burned paddies contained 63% less rice straw than paddies with standing stubble in February 2005, which is good news for the Monsanto Farm and other rice producers. "However, research is needed to replicate Havens' research throughout the MAV to determine if waterfowl and rice-straw responses observed on the Monsanto Farm are consistent on a broad scale," said Kaminski.

Flooding standing or burned rice stubble may maximize availability of waste rice for waterfowl most economically, because tractor and other implement costs are eliminated. However, if environmental regulations or agricultural practices prevent stubble burning, the scientists suggest mowing "patches" within fields to create open-water areas following flooding, because the mowing treatment conserved waste rice above the "giving-up" threshold. Managers who prefer to roll or disk stubble should do so sparingly, because these treatments resulted in waste-rice densities at or below the "giving-up" threshold.

Dr. Richard M. Kaminski is a Professor in the Department of Wildlife and Fisheries at Mississippi St