In a semiarid Mediterranean site in central Spain, field experiments were conducted on a Calcic Haploxeralf (noncalcic brown soil), which had been managed with three crop rotations and two tillage systems (no-tillage and conventional tillage) since 1987. The crop rotations consisted of barley→vetch, barley→sunflower, and a barley monoculture. The study took place in two growing seasons (1992–1994) to assess the effects of management practices on the weed seedbank. During this period, spring weed control was not carried out in winter crops. In the no-tillage system, there was a significant increase in the number of seeds of different weed species: anacyclus, common purslane, corn poppy, knotted hedge-parsley, mouse-ear cress, spring whitlowgrass, tumble pigweed, venus-comb, and Veronica triphyllos. Conversely, the presence of prostrate knotweed and wild radish was highest in plots under conventional tillage. These results suggest large differences in the weed seedbank as a consequence of different soil conditions among tillage systems, but also the necessity of spring weed control when a no-tillage system is used. With regard to crop rotations, the number of seeds of knotted hedge-parsley, mouse-ear cress, and spring whitlowgrass was greater in the plots under the barley→vetch rotation. Common lambsquarters dominated in the plots under the barley→sunflower rotation, whereas venus-comb was the most frequent weed in the barley monoculture. Larger and more diverse weed populations developed in the barley→vetch rotation rather than in the barley→sunflower rotation or the barley monoculture.

Field studies were conducted over 3 yr to investigate the effect of chemicals on field beans density and weed control. Predominant weed species were common lambsquarters, fumitory, henbit, corn poppy, prostrate knotweed, and wild mustard. All herbicide treatments except linuron injured field beans. Mean field beans survival at harvest was 78% in alachlor and 84% in alachlor containing treatments. Only 5% survived atrazine at 1.9 kg ai ha−1. Ethalfluralin, pendimethalin, simazine, terbutylazine plus terbutryn, and trifluralin treatments produced plant survival values of 56, 82, 86, 74, and 71%, respectively. Chemical control of the main weed species overshadowed the detrimental effect on field beans density, and thus most herbicide treatments except alachlor resulted in increased dry beans yield. The best overall results occurred with linuron, simazine, terbuthylazine plus terbutryn, and pendimethalin which increased dry beans yields 76, 63, 56, and 40%, respectively, over the control plots. Common lambsquarters was the dominant weed, and prostrate knotweed and corn poppy were the most difficult and the easiest species to control, respectively.

Clods of three sizes (1.5-, 3.3-, and 5.3-cm diameter) and two hardnesses [soft (0.3 MPa) and hard (2.2 MPa)] were made by incorporating seed from one of the five following weed species: corn poppy (Papaver rhoeas L. # PAPRH), shepherdspurse [Capsella bursa-pastoris (L.) Medic. # CAPBP], smooth crabgrass Digitaria ischaemum (Schreb.) Muehlenb. # DIGIS], common lambsquarters (Chenopodium album L. # CHEAL), and Canada thistle [Cirsium arvense (L.) Scop. # CIRAR], listed by increasing seed size. Under conditions of this experiment, higher germination occurred with larger seed. The higher germination was connected with fewer dormant seed remaining in the clods. Germination significantly decreased (13%) in the larger soft and hard clods with the smaller seed sizes (less germination associated with more dormant seed remaining in the clod). Germination of the two larger seed decreased (23%) only in the larger soft clods but was less significant with both small seed. Non-emerged seedlings increased with larger clods and was most significant with the three large seed in the hard clods and absent with the three large seed in the soft ones. On the average, 70% of the germinated seed emerged. Differences in germination as well as in nonemerged seedlings caused decreased emergence on larger clods. Clod influence in germination and emergence was explained by the volumes of the clod layers involved, and in some comparable aspects corresponded with volumes (depths) of soil layers.