Use of¹³C Isotope Discrimination Analysis to Quantify Distribution of Barnyardgrass and Rice Roots in a Four-Year Study of Weed-Suppressive Rice

Abstract

In a 4-yr field study, “weed suppressive” rice cultivars provided 30% greater control of barnyardgrass and sustained 44% less yield loss (relative to weed-free) compared to “nonsuppressive” tropical japonica rice cultivars. 13C analysis revealed that rice root mass predominated vertically and laterally within the soil profile of plots infested with barnyardgrass. Among all cultivars, rice roots accounted for 75 to 90% of the total root mass in samples, and this was most concentrated in the surface 5 cm of soil in the row. Barnyardgrass roots were most prevalent in the surface 5 cm between rows where they accounted for 30% of total root mass. Overall, barnyardgrass root mass was about twice as high in nonsuppressive rice compared to suppressive rice. Weed suppression by indica/tropical japonica rice crosses generally was intermediate between that of the other two rice groups. At the 0- to 5-cm depth, between-rows, barnyardgrass root mass was correlated negatively with rice height (r = −0.424), yield (r = −0.306), and weed control ratings (r = −0.524) in weedy plots. Control ratings in weedy plots also were negatively correlated with rice percent height reduction (r = −0.415) and % yield loss (r = −0.747) relative to weed-free plots, and with barnyardgrass root mass as a percent of total root mass (r = −0.612). Control ratings were positively correlated with rice yield under weed pressure (r = 0.429) but were correlated with rice root mass in-rows only (r = −0.322). Clearly, rice root mass could not have been the major cause of the differences in barnyardgrass control between cultivars.

Fine-root traits of allelopathic rice at the seedling stage and their relationship with allelopathic potential

“…Dilday, Mattice & Moldenhauer (2000) first previously reported that allelopathic rice cultivars had the greatest root biomass than non-allelopathic rice cultivars in field test. Until recently, Gealy et al also observed that the root distribution of allelopathic rice cultivars is shifted towards the upper soil with relatively greater root biomass in comparison to non-allelopathic rice cultivars (Gealy & Moldenhauer, 2012; Gealy, Moldenhauer & Duke, 2013). In addition, these root traits were significantly-positively correlated to allelopathic inhibition and total phenolic contents in rice root-exudates (Table 3), which has not been reported before.…”

Genetic potential of rice under alternate-wetting-and-drying irrigation management for barnyardgrass (Echinochloa crus-galli) suppression and grain yield production

“…Replicated field experiments on seven diverse rice genotypes (Table 1) were conducted in 2012, 2013, and 2014 at the Dale Bumpers National Rice Research Center and University of Arkansas Rice Research and Extension Center located near Stuttgart, AR (34.49°N, 91.55°W). The soil was a DeWitt silt loam (fine smectitic, thermic, Typic Albaqualfs) with 1.2% organic matter and a pH of 5.8, as described previously (Gealy and Fischer 2010;Gealy and Moldenhauer 2012).…”

“…Rice genotypes that suppress weeds naturally through either allelopathic mechanisms or increased competitiveness have the potential to contribute to IWM systems that would reduce reliance on synthetic herbicides while maintaining adequate management of weeds. Many such genotypes have been investigated throughout the world (Chen et al 2008;Kato-Noguchi and Ino 2005;Khanh et al 2007;Kong et al 2006Kong et al , 2011Seal and Pratley 2010;Thi et al 2014;Worthington and Reberg-Horton 2013), and a few have been evaluated in the southern United States (Gealy et al 2003(Gealy et al , 2005(Gealy et al , 2013aGealy and Moldenhauer 2012;Watkins et al 2018). However, none of these has been tested under alternate-wettingand-drying(AWD) irrigation systems in the southern United States.…”

Effect of Seeding Rate on Weed-Suppression Activity and Yield ofIndicaand TropicalJaponicaRice Cultivars

“…To establish baseline productivity levels for the rice cultivars, rough rice grain yield and other biological variables were determined for the weed-free checks. The relative impact of weeds on the different rice cultivars was assessed by calculating a percent reduction of productivity variables compared with the weed-free rice plots, as described previously (Gealy and Moldenhauer 2012).…”