Weeds and the soil environment - Ecological Management of Agricultural Weeds - page 226

Figure 5.4 Shoot dry weight ofmaize and Amaranthus retroflexus as influenced by
form ofN fertilizer.Nitrogen was supplied as either calcium nitrate or
ammonium sulfate with a nitrification inhibitor.Individual maize plants were
grown in pots for 23 days before harvest; A.retroflexus was grown at a density of2
plants per pot for 37 days before harvest.(After Teyker,Hoelzer & Liebl,1991.)

a mixture of urea and ammonium nitrate (UAN). Total amounts of N applied
in the different fertilizers were equal, but distinct differences were observed
between treatments in the abundance of various weed species. Galeopsis tetra-
hit , Veronica persica, Thlaspi arvense , and Stellaria media were all relatively abun-
dant in fields fertilized with AS or CAN,but were not detected in fields treated
with UAN. Conversely, Apera spica-venti was observed in 8% of the quadrats

sampled in fields fertilized with AS or CAN, but in 40% of the quadrats from
the area fertilized with UAN. Although most of the weed species were simi-
larly abundant in the AS and CAN treatments, Fallopia convovulus was present
in 79% of the CAN quadrats, but only 41% of the AS quadrats. Total weed
infestation, expressed as the estimated amount of weed cover in the sample
quadrats, was least in the UAN treatment, greatest in the CAN treatment, and
almost as high in the AS treatment.Statistical analyses indicated that the weed
community was influenced both directly by fertilizer treatments and indi-