Crop husbandry for weed management

B. Frick, E. Johnson - Scott Research Farm

Problem

What is crop husbandry? How is it important for weed management?

Background

One of the most effective weed management tools is good crop husbandry. A strong and competitive crop offers less opportunity for weeds. All crop management techniques that contribute to good growth can be considered weed management tools. Crops can compete well with weeds if they establish quickly and uniformly, are vigorous, and well nourished. Agronomic recommendations are often assembled from results obtained in virtually weed free experimental plots. A combination of sowing time, crop genotype, crop planting arrangement, crop density and fertilizer input that's optimal under weed free circumstances is not necessarily optimal in weedy fields. Moreover, desirable husbandry practices can contribute considerably to weed control at very little extra cost.

Two primary principles of crop husbandry relate to weed management:

• vary farm practice to avoid having weeds adapt to it
• whenever possible, give advantage to the crop, not the weed.

Varying farm practice prevents weeds that prosper in one system from gaining too strong an advantage. Many factors can be varied to ‘confuse’ the weeds. These include:

• extensive and varied crop rotations
• alternating timing of operations such as seeding and harvest
• varying tillage amount and timing
• modifying soil fertility through green manures, livestock manures and other soil amendments, and using crops that deplete nutrients to a greater or lesser extent.

Slight alterations of existing practices are often enough to change their relative advantage. For instance, on-row packing, rather than packing the entire field may give an advantage to the crop relative to most of the weeds. Banding liquid manures near the crop row, rather than across rows may mean a relatively greater share of them goes to the crop.

Seeding rates and patterns can also have an effect on how well a crop competes. High seeding rates and narrow row spacing decrease the distance between crop plants, and the canopy closes sooner. This reduces weed seedling germination, and gives the crop an edge in early competition. The disadvantages are increased seed costs, and lessfeasible inter-row cultivation.

High seeding rates are especially helpful on weedy land. On weedfree land, high seeding rates offer no advantages over recommended seeding rates. Green feed and silage crops can be seeded at higher rates to increase crop competition and feed quality. Increased seeding rates should also be used if either postseeding or postemergence tillage is planned. This will help compensate for any damage caused by in-crop tillage. An increase of 25% above normal is often recommended. High seeding rates may be advantageous in a dry year if seedlings more effectively cover the soil and reduce evaporation from the soil surface. If there is enough moisture, high seeding rates will speed maturity (two to three days), and result in shorter plants with fewer tillers. Under certain environmental conditions, higher seeding rates may increase disease incidence or may result in higher lodging losses.

In one Saskatchewan study, increasing peas' seeding rate reduced weed numbers; high pea populations competed well with weeds. In another study at Scott, barley yielded the most at narrow row spacing and increased seeding rate.

Weed biomass was reduced by both narrower row spacing and increased seeding rate. Narrow row spacing allows crops to fill the available space more completely, leaving less space for weeds. Cross-seeding is another alternative that needs no machinery modification, but has much the same effect.

Conclusions

Good crop husbandry is an effective weed management system. Two primary principles of crop husbandry relate to weed management:

• vary farm practice to avoid having weeds adapt to it
• whenever possible, give the advantage to the crop, not the weed.

Practices recommended for weed-free conditions may need to be altered for weedy conditions. High seeding rates, and close planting patterns leave less opportunity for weeds.

Acknowledgements

Funding provided by the Canada-Saskatchewan Agri-Food Innovation Fund

Originally published in Research Report 2002, Canada-Saskatchewan Agri-Food Innovation Fund