Estimation of economic threshold level of alligator weed (Alternanthera philoxeroides (Mart.) Griseb.) to Tackle Grain quality and yield Losses in Rice

Alligator weed (Alternanthera philoxeroides) is the most troublesome invasive weed in transplanted rice ecosystems worldwide. A two-year field study was conducted to estimate economic threshold levels and the season long competitive effect of six alligator weed densities (0, 2, 4, 8, 16, and 32 plants m(-2)) on yield and quality traits of transplanted rice. A gradual linear incline in dry weight of alligator weed was observed with an increase in its density from 2 to 32 plants m(-2). Maximum N (15.93-18.26kg ha(-1)), P (15.10-16.46kg ha(-1)) and K (16.34-17.81kg ha(-1)) uptake by alligator weed was recorded at its density of 32 plants m(-2). More micronutrient loss to the tune of 6.53, 47.92, 19.99, and 38.42mg kg(-1) for Cu, Fe, Zn, and Mn, respectively was observed at the same density. Increasing density of alligator weed caused more losses in paddy yield (up to 21.37-23.78%), amylose and rice grain protein contents. According to a nonlinear hyperbolic regression model, maximum paddy yield loss of rice at asymptotic value of alligator weed density was 38.8% during 2011 and 42.4% during 2012. Economic threshold value of alligator weed was estimated 1.5 and 1.3 plants per m(2) during 2011 and 2012, respectively.