Location: Soil, Water & Air Resources ResearchTitle: Nitrogen cycling under alternate wetting and drying cycles in Arkansas rice Author
|Olk, Daniel - Dan|
|Anders, Merle - University Of Arkansas|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/18/2017
Publication Date: N/A
Technical Abstract: Alternate wetting and drying (AWD) cycles offer potential savings in water use for paddy rice production while reducing both greenhouse gas emissions and lowering grain arsenic content. In a three-year (2011-2013) field study near Stuttgart, AR, one-third of a field previously grown to soybean was brought into continuous rice production for three consecutive years, enabling within-season comparison of first-year rice versus second-year rice (2012) and also versus third-year rice (2013) while avoiding differences in annual weather patterns. Within each year’s rice area, season-long AWD (with drying to 60% of soil water-holding capacity) was compared to season-long AWD to 40% of field moisture capacity and to AWD (drying to 40%) only during vegetative growth stages followed by maintained flood during reproductive growth stages. The AWD treatments began 14 days after the initial flood. The control was permanent flood throughout the growing season. In the second and third years, N cycling was investigated through 15N microplots imbedded within three of the four field replicates. Rice uptake of 15N estimated crop uptake of fertilizer N, and rice uptake of 14N estimated crop uptake of soil N. Grain yield decreased by 5% with season-long AWD (drying to 60% drying) compared to the flood control, and any N uptake decrease was insignificant. For continuous rice, grain yield did not decrease in the treatment having AWD during vegetative growth only followed by maintained flood during reproductive growth, which we attribute to a late-season increase in available soil N as measured in the 15N microplots. At harvest, continuous rice had taken up 20 to 47 kg N ha-1 more in this treatment than in the full-season-long AWD or even the continuous flood control, due mostly to the late-season soil N flush. The size of this N flush grew during the three years of the study, possibly reflecting a gradual accumulation of higher quality soil organic matter resulting from more aerobic decomposition of crop residues. The aeration treatments had no clear effect on N cycling or yield trends for first-year rice. All aeration treatments for first-year rice had greater grain yield and N uptake than did all continuous rice treatments, especially for third-year rice. The evolution of this yield gap during second- and third-year rice cropping was driven by further decreases in crop uptake of soil (14N) nitrogen, consistent with our earlier research on an observed yield gap between long-term continuous rice versus rice-soybean cropping.