SEED BANK CHARACTERIZATION AND EMERGENCE OF A WEED COMMUNITY IN A MOLDBOARD PLOW SYSTEM

Field experiments were conducted in 1992 and 1993 to characterize the weed seed bank, to determine the influence of moldboard plowing and se condary soil disturbance on the emergence pattern of weeds, and to mea sure weed seed bank depletion by emergence in a long-term moldboard pl ow corn cropping system. Viable seeds of common lambsquarters, redroot pigweed, and each of 10 other species accounted for about 85, about 9 , and less than 1%, respectively, of the total weed species in the see d bank. A negative binomial distribution described che spacial distrib ution of viable seeds of 10 species, but not of common lambsquarters o r of redroot pigweed. Decreased density of seeds among species was ass ociated with increased aggregation. Secondary soil disturbance increas ed the rate and magnitude of common lambsquarters emergence in 1992 bu t did not influence emergence in 1993. Secondary soil disturbance did not influence the magnitude and rate of emergence of redroot pigweed o r velvetleaf. Whereas cumulative growing degree days from April throug h July were similar between years, the amount of rainfall was about 50 % less in 1992 than in 1993. Secondary soil disturbance may have incre ased common lambsquarters emergence by increasing the availability of soil moisture and improving conditions for seed germination during the dry year. Even though seed bank depletion by seedling emergence was r elatively low for all species, secondary soil disturbance increased se ed bank depletion of common lambsquarters and redroot: pigweed about 7 - and 3-fold, respectively, in 1992. Seasonal variation in the amount of rainfall may have influenced the effect of soil disturbance on emer gence and seed bank depletion of common lambsquarters, which is the mo st abundant species in the weed community.