|Anders, M - UNIVERSITY OF ARKANSAS|
|Grantham, J - UNIVERSITY OF ARKANSAS|
|Holzhauer, J - UNIVERSITY OF ARKANSAS|
Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 3, 2004
Publication Date: January 10, 2005
Citation: Olk, D.C., Anders, M.M., Boeckmann, J.M., Grantham, J., Holzhauer, J. 2005. Impaired cycling of soil nitrogen under continuous rice rotations in the arkansas grand prairie area. Rice Technical Working Group Meeting Proceedings. p. 148-149. Technical Abstract: For economic reasons a continuous rice (Oryza sativa L.) rotation in eastern Arkansas may expand at the expense of the conventional rice-soybean (Glycine max. (L.) Merr.) rotation. In a 4-year field experiment at Stuttgart, AR, continuous rice yielded 12 to 23% less grain than rice following soybean, likely due to a late-season nitrogen (N) deficiency. To study the cycling of fertilizer N and soil organic N, in 2002 we applied 168 kg 15N-labeled urea N ha-1 to the Stuttgart experiment. Rice plants were harvested from separate microplots at the green ring growth stage (83 days after emergence, DAE), 50% heading growth stage (103 DAE), and harvest (133 DAE). Soil samples were also taken for determination of their 15N content and phenols content. Crop uptake of labeled fertilizer N occurred largely during early growth stages and was greater in the rice-soybean rotation than in continuous rice, the difference increasing from 7 kg N ha-1 at green ring to 14 kg N ha-1 at harvest. Crop uptake of unlabeled soil N continued throughout the crop season; it was 6 kg ha-1 greater in rice-soybean than in continuous rice at green ring and 50% heading and 24 kg ha-1 greater at harvest. Continuous rice soils had higher levels of phenolic compounds than did rice-soybean soils, being enriched by 46% for ferulic acid and p-hydroxycinnamic acid and by 16 to 25% for syringyl phenols. 15N gradually accumulated under continuous rice, being more abundant than under rice-soybean by < 1 kg ha-1 in the plow layer at green ring and by 14 kg ha-1 at harvest. The accumulation of phenolic compounds under anaerobic soil conditions was accompanied by (i) slowed late-season mineralization of organic N and immobilized urea N, (ii) an apparent late-season N deficiency in the rice crop, and (iii) a rice yield gap.