Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2006
Publication Date: May 15, 2006
Citation: Burgos, N.R., Norman, R.J., Gealy, D.R., Black, H.L. 2006. Competitive N uptake between rice and weedy rice. Field Crops Research. 98(1):1-7. Interpretive Summary: Weedy rice (Oryza sativa L.), called red rice in the U.S., is a serious problem in rice of the southern U.S. and worldwide. Because nitrogen (N) fertilizer is expensive and needed by both rice and red rice in large amounts, research was conducted in 1999 and 2000 at Stuttgart, Arkansas to compare several measures of nitrogen fertilizer uptake and distribution in rice and red rice growing competitively in field soil. Nitrogen in the form of urea fertilizer labeled with small amounts of a stable isotope (15N) was applied at rates of 0, 5, 10, 15, and 20 g m-2 to field plots planted to both Drew rice and strawhull red rice (10 to 15 g m-2 is a typical field rate). Levels of fertilizer nitrogen were then measured in various shoot tissues (lower leaf, leaf sheath, top leaf, and panicle) at both the panicle initiation stage (PI) and at two weeks after heading (WAH). Red rice and Drew rice produced similar shoot biomass without added fertilizer. However, the response of red rice to 5 g N m-2 was two to three times greater than that of Drew, and this difference increased with N rate. In general red rice responded to higher N rates, took up more N, and had higher N use efficiency for biomass production than rice. These results indicate that controlling red rice should be the priority when rice fields are heavily infested with this weed. Otherwise, fertilizer N application (which is more expensive than red rice control) will not be profitable.
Technical Abstract: Weedy rice, red rice (Oryza sativa L.), is a serious problem in rice-producing areas of the southern U.S. and various regions worldwide. It competes for production inputs, increases weed control costs, reduces yield and grain quality, and could eliminate economic returns. Research was conducted to compare: i) the relative efficiencies of rice and weedy rice in recovering fertilizer N under a competitive condition, ii) the accumulation and partitioning of N by rice and weedy rice, and iii) the N use efficiency of rice and weedy rice. Experiments were conducted in 1999 and 2000 at the Rice Research and Extension Center, Stuttgart, Arkansas, USA. Experimental units were arranged in a split-split-plot design with N rate (0, 5, 10, 15, and 20 g m-2) as mainplot, plant type (rice and weed rice) as subplot, and type of shoot tissue (lower leaf, leaf sheath, top leaf, and panicle) as the sub-subplot. Drew rice and strawhull red rice were drill-seeded in alternate rows. At 26 to 27 days after planting, metal collars were driven into the soil to establish two microplots per treatment. Urea labeled with 15N was applied to dry soil in the microplots immediately before permanent flood. Data were collected at panicle initiation (PI) and two weeks after heading (WAH). Regardless of harvest dates, Drew rice and weedy rice produced equivalent shoot biomass when no fertilizer N was added. The response of weedy rice to 5 g N m-2 was 1.75 times more than that of Drew at PI and 3 times more at 2 WAH. The difference in shoot biomass production between Drew and weedy rice became larger as N rate increased. At 2 WAH, weedy rice had more culm biomass (58% of total) than Drew (48%). Lower leaves constituted 16 to 19% of total shoot biomass, flag leaf 6%, and panicles comprised the rest for both plant types. Weedy rice accumulated more N, responded to higher N rates, accumulated more N in the panicles, and had a higher N use efficiency (in terms of biomass production) than Drew rice. Weedy rice can accumulate 60% of applied fertilizer N, 2 WAH. We conclude that weedy rice responds to higher N rates, takes up more N, and has higher N use efficiency for biomass production than rice. Whenever a rice field is heavily infested with weedy rice, controlling weedy rice should be the priority. Otherwise, fertilizer N application (which is more expensive than weedy rice control input) is not profitable.