Abstract
Tillers production is the earliest yield component in wheat and contribute significantly to final grain yield. To assess this concept, field study was conducted during 2003-04 and 2004-05 at Malankandher Research Farm, NWFP Agricultural University Peshawar. The experiment was conducted using randomized complete block design with split-plot arrangement. Seed rates of wheat at 100, 120, 140 and 160 kg ha-1 were assigned to main plots while Holy thistle (Silybum marianum) densities at 0, 3, 6, 9, 12, 15 and 18 m-2 were assigned to sub-plots. Regression analyses of the data showed that at seed rate 100, 120 and 140 kg ha-1 , the tillers m-2 decreased linearly with the increase in Silybum density while seed rate at 160 kg ha-1 was affected quadratically. Overall, seed rate at 120 kg ha-1 gave maximum tillers. At lower seed rates, interspecific and at higher seed rates intraspecific competition decreased tillers. However, the magnitude of tillers reduction was seed rate and year dependent; greater reduction at lower seed rates rather than at higher seed rate. Similarly the magnitude of tillers reduction was greater during 2004-05 as compared to 2003-04. This year’s difference could be attributed to the higher rainfall and low temperature during 2004-05 that favoured the growth of S. marianum and thus proved more harmful to the wheat as compared to 2003-04. Thus it can be concluded from the results that seed rate as well as environmental conditions play an important role in manipulating the crop-weed competition and tillers in wheat.
