This is demonstrated by the higher yields achieved with the certified seed sources. How you prepare your seedbed can affect crop and weed growth. Ensuring that the crop seed is placed in an ideal growing environment, and the weeds are not, is another way to give your crop the edge. On-row packing leaves the soil in the row firm, but loose in between the rows. Zero-tillage systems leave crop residue in between the rows, which shades the soil and keeps it cool.
Fewer weeds germinate under zero-tillage because of the reduction in soil disturbance.
Certain crop varieties can be more competitive than others. Semi-dwarf wheat varieties are generally less competitive than regular varieties. Taller varieties close their crop canopies more completely than shorter types, which helps shade out weeds. This is also true of pea varieties. You may still need to spray the taller varieties, but your weed control will be better because of the added crop competition.