A, The ESTIMATION OF ECONOMIC THRESHOLDS OF JUNGLE RICE (ECHINOCHLOA COLONA L.) AND FALSE AMARANTH (DIGERA ARVENSIS FORSSK.) IN DIRECT SEEDED RICE

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.