Field experiments were conducted in 1997 and in 1998 to determine the effects of density and time of emergence onEriochloa villosagrowth and seed production inZea mays. E. villosawas transplanted at four densities (3, 9, 27, and 81 plants m−2) to simulate emergence at four Z.maysgrowth stages (VE, V2, V5, and V10). Compared toE. villosaplants that emerged withZ. maysplants, total above-groundE. villosabiomass at maturity of plants grown at 3 plants m−2was reduced by 54, 97, and 99% when emergence was delayed until the V2, V5, and V10 stages ofZ. mays, respectively, in 1997. In 1998, total abovegroundE. villosabiomass at maturity was reduced by 70, 87, and 99% when emergence was delayed until the V2, V5, and V10 stages ofZ. mays, respectively.E. villosaaboveground vegetative biomass per plant at maturity was linearly related to seed production per plant in each year.E. villosaseed production m−2decreased nonlinearly as density decreased and time of emergence was delayed. Based on estimated model parameters, maximum seed production was 57,100 and 12,700 seeds m−2in 1997 and 1998, respectively. Within time of emergence,E. villosadensity did not affect seed mass per seed, however, seed mass of late-emerging cohorts was less than that of early-emerging cohorts. Time of weed emergence relative to the crop was a very important factor in determining biomass and seed production. Results suggest that late-emerging plants may not be very important to long-term management ofE. villosa.
Long-term Variation of Rainfall in the Far East
