Cover crop and irrigation impacts on weeds and maize yield

Winter cover crops (CC) may facilitate weed management by inhibiting weed
seed germination and seedling emergence and suppressing weed growth within
the cash crop. In southern New Mexico, with scarce winter precipitation
and limited irrigation water, producing sufficient CC biomass for
effective weed suppression while conserving water resources is
challenging. This study assessed the water requirement to produce a CC
with enough biomass for weed suppression benefits during cash crop growth
at two locations in New Mexico. Three winter CC species, barley, Austrian
winter pea and mustard, grown singly and in a three‐way mix, under three
differential irrigation treatments (one, two or three irrigations after
emergence) were evaluated for their weed‐suppressive potential. Maize was
planted as a cash crop four weeks after winter CC termination. Number of
irrigations had no effect on the CC and weed biomass production. All CCs
had lower weed density prior to maize planting compared with fallow.
Barley and the three‐way mix reduced weed density by 56–96% and 68–95%,
respectively. All CC treatments had lower weed biomass at the end of
critical period for weed control in maize compared with fallow. Weed
biomass at maize harvest did not differ between treatments. The maize
yield was consistently higher in conventionally managed, weed‐free
subplots, than in unsprayed weedy subplots, suggesting that CCs did not
suppress weeds throughout the maize growing season. Except for barley, CCs
did not cause reductions in maize yield compared with fallow. Overall, the
study suggested that with adequate winter precipitation, weed‐suppressive
winter cover crop stands can be produced with just one irrigation at
seeding and one supplemental irrigation, making them a viable option in
water‐limited agroecosystems.