Improving upon the interrow hoed cereal system: the effects of crop density and row spacing on intrarow weeds and crop parameters in spring barley

Automated guidance systems have advanced precise interrow hoeing in narrowly spaced cereals.
Compared with other direct mechanical strategies, hoeing provides superior weed control
and improved yields. However, weeds in the uncultivated intrarow zone may survive and compete
intensely with the crop, causing yield loss. Therefore, improved intrarow weed management
strategies in hoed cereals must be investigated. In spring barley (Hordeum vulgare L.), the
effect of crop density was assessed at four levels (200, 300, 400, and 500 plants m−2); interrow
spacing at two levels (15 and 20 cm), relevant to the abilities of current automated equipment to
hoe between narrowly spaced rows; and weed management treatment at three levels (no additional
controls, herbicide, and preemergence tine harrowing). All treatments received interrow
hoeing, and a surrogate weed (white mustard, Sinapis alba L.) was sown and monitored
throughout experiments. The manipulation of crop density was a reliable method for suppressing
the growth of intrarow weeds. As barley density increased from the target 200 to
500 plants m−2, percent reduction in intrarow surrogate and ambient weed biomass (g m−2)
increased from 49% to 82% and 53% to 99%, respectively. Increasing crop density caused a
decrease in grain bulk density (kg hl−1) both years, and grain protein (%) and 1,000-kernel
weight (g) in one year; whether these changes constitute a loss in grain quality depends upon
end use. While row spacing had no effect on intrarow weeds, crop yields were 7% to 8% lower at
20 cm compared with 15 cm, incentivizing narrow row sowing. Barley yields were unaffected by
increasing crop density, and the effect of preemergence tine harrowing was inconsistent. In one
year, harrowing reduced surrogate and ambient weed biomass and increased barley yield; however,
in another year, ambient weed biomass increased, and harrowing did not affect yield or
surrogate weed biomass.