Role of seed reproduction in the population ecology of Sorghum halepense in maize crops.
Abstract
The contribution of seed reproduction to population growth of S. halepense was studied on an 80-ha maize field in Rojas province, Buenos Aires during 1984-87. Seed production in dense patches was very high (8080±4300 whole seeds/m2) and 90% of the total seed yield was produced during Dec. and early Jan. Shedding of seed began 30 days after panicle emergence. Daily seed shedding in dense patches ranged from 75 to 100/m during most of the summer. After an initial rise in Jan., seed density on the soil surface decreased about 5-fold during the summer months. Seed losses from the soil surface varied between 3 and 15%/day during the crop cycle, and betwen 20 and 50%/day during the fallow period. Loss of seed was substantially reduced by seed burial and completely prevented if seeds were covered with 5 mm plastic mesh. Seedlings emerged the month after sowing maize. Av. seedling suvival was 25%, between-row cultivation being the main cause of mortality. The average fecundity of seed plants was 41 seeds/plant; 40% of the established plants produced seeds. A simple model indicated that the potential for multiplication during the plant phase is about 4 seeds per seedling per year. However, when losses during the seed phase were incorporated in the model, the multiplication rate of a population reproducing solely by seeds is substantially lower than one. It is inferred that reproduction by seeds would not maintain the population under continuous maize.