Abstract

ABSTRACT There is little understanding about ecological interference of weeds in direct-seeded rice. To get estimates of economic thresholds of two weeds in direct seeded rice, two-year field trials were conducted at research area of College of Agriculture, University of Sargodha, Punjab-Pakistan. Treatments included 0, 22, 44, 66 and 88 plants m-2 densities of each of Echinochloa colona and Digera arvensis laid out in randomized complete block design. Augmented densities of E. colona (0, 22, 44, 66 and 88 weed plants m-2) enhanced its plant dry biomass up to 348 and 353%; and relative competitive index maximally to 80 and 77% in years 2015 and 2016, respectively. While the corresponding increases in plant dry weight and relative competitive index of D. arvensis were 367 and 360% and 79 and 82%. The enhancement in N (up to 258 & 257 %), P (up to 220 & 232%) and K (up to 293 & 301%) uptake in years 2015 and 2016, respectively were made by E. Colona whereas the corresponding increases in N, P and K assimilation by D. arvensis were as far as 265 & 257%, 238 & 233% and 305 & 298%, respectively. The declines in growth and yield of rice were observed in response to growing number of both the weeds. Rice grain yield losses ranged between 9.8 to 80% and 28 to 80% by E. Colona and D. arvensis. The economic thresholds of false amaranth and jungle rice were estimated to be 1.6-1.4 plants m-2 and 2.2-2.6 plants m-2, respectively.

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