Ecological significance of rice (Oryza sativa) planting density and nitrogen rates in managing the growth and competitive ability of itchgrass (Rottboellia cochinchinensis) in direct-seeded rice systems

Abstract

Ecological significance of rice (Oryza sativa) planting density and nitrogen rates in managing the growth and competitive ability of itchgrass (Rottboellia cochinchinensis) in direct-seeded rice systems Abstract Current understanding is that high planting density has the potential to suppress weeds and crop-weed interactions can be exploited by adjusting fertilizer rates. We hypothesized that (a) high planting density can be used to suppress Rottboellia cochinchinensis growth and (b) rice competitiveness against this weed can be enhanced by increasing nitrogen (N) rates. We tested these hypotheses by growing R. cochinchinensis alone and in competition with four rice planting densities (0, 100, 200, and 400 plants m -2 ) at four N rates (0, 50, 100, and 150 kg ha -1 ). At 56 days after sowing (DAS), R. cochinchinensis plant height decreased by 27-50 %, tiller number by 55-76 %, leaf number by 68-84 %, leaf area by 70-83 %, leaf biomass by 26-90 %, and inflorescence biomass by 60-84 %, with rice densities ranging from 100 to 400 plants m -2 . All these parameters increased with an increase in N rate. Without the addition of N, R. cochinchinensis plants were 174 % taller than rice; whereas, with added N, they were 233 % taller. Added N favored more weed biomass production relative to rice. R. cochinchinensis grew taller than rice (at all N rates) to avoid shade, which suggests that it is a ''shade-avoiding'' plant. R. cochinchinensis showed this ability to reduce the effect of rice interference through increased leaf weight ratio, specific stem length, and decreased root-shoot weight ratio. This weed is more responsive to N fertilizer than rice. Therefore, farmers should give special consideration to the application timing of N fertilizer when more N-responsive weeds are present in their field. Results suggest that the growth and seed production of R. cochinchinensis can be decreased considerably by increasing rice density to 400 plants m -2 . There is a need to integrate different weed control measures to achieve complete control of this noxious weed.

Competitive Effects Hinder the Recolonization of Native Species in Environments Densely Occupied by One Invasive Exotic Species

“…The largest investment in shoots by L. hexandra at high densities of the invasive probably occurs because Poaceae are, in general, highly sensitive to shading conditions. Allocation to shoot biomass, relative to root biomass, is likely to be a response to light limitation under high competition, as observed for other herbaceous species ( Gibson et al, 2004 ; Awan et al, 2015 ). On the other hand, increased allocation to roots in P. cordata indicates a response to root competition (for other examples, see Bakker and Wilson, 2001 ; Schiffers et al, 2011 ; Zhu et al, 2015 ).…”

Responses of AG1 and AG2 QTL introgression lines and seed pre-treatment on growth and physiological processes during anaerobic germination of rice under flooding

“…Our study showed that seedling emergence had significant positive correlation with SVI (r = 0.96, P < 0.001), LAI (r = 0.90, P < 0.001), plant biomass (Pearson correlation, r = 0.59, P < 0.001). Previously researchers also reported that, seedling emergence correlated positively with SVI 16,47 , leaf area index (LAI) 47,48 and plant biomass production 15 . This has also been observed in other crops, including sorghum (Sorghum bicolor) 49 and sunflower (Helianthus annuus) 23 .…”

“…Growth parameters (seedling root and shoot length) were measured at 6, 10, 15, and 21 days after sowing (DAS) on 12 seedlings 48,66 . Seedling emergence percentage was calculated at 21 days after sowing based on the number of seedlings that emerged above the surface of floodwater following the below formula 1 .…”

“…Physiological traits including non-structural carbohydrates (starch and soluble sugars), α-amylase activity, concentrations of ascorbate and total phenolic compound, ROS scavenging activity, and lipid peroxidation were www.nature.com/scientificreports www.nature.com/scientificreports/ analyzed 1,12,48 . The methods and techniques used to measure the physiological traits are all well established and widely used, and they are just briefly described here with reference to relevant papers for more details.…”

Performance of Pre- and Post-emergence herbicides in strip tillage Non-puddled transplanted Aman rice

“…Butachlor fb orthosulfamuron fb butachlor + propanil also provided similar number of panicles m -2 and pyrazosulfuron-ethyl fb orthosulfamuron fb 2,4-D amine gave similar number of filled grains panicle -1 with weed-free control. This might be happened for ensuring better weed control by those treatment that leads to reduced crop-weed competition and facilitated the uptake of more nutrients resulted healthier rice plants with more tillers and panicles (Ahmed and Chauhan, 2014;Awan et al, 2014). 'fb' = 'followed by', 'aceto + bensul' = 'acetochlor + bensulfuron methyl', 'orthosul' = 'orthosulfamuron', 'buta + prop' = 'butachlor + propanil', '2,4-D' = '2,4-D amine', 'CV' = co-efficient of variance…”