Crop rotation is essential for the effective control of soil- and residue-borne diseases of wheat. Without crop rotation these diseases can result in serious yield losses. For example, after three or four years of wheat-after-wheat, common root rot can reduce yields of some wheat cultivars (varieties) by up to 20 percent, and take-all may cause yield losses exceeding 70 per cent. (However, in continuous wheat the take-all level may stabilize after these very high yield losses, at less than 5 percent yield loss. The reason for this is unknown.) A three- or four-year rotation with wheat will greatly reduce the buildup of soil- and residue-borne diseases.
Crop residue effects:
The crop residue cover on direct seeded fields conserves soil moisture and traps snow. Thus seeding depths can be shallower in direct seeded fields. Shallow seeding results in earlier emergence and more vigorous seedlings better able to withstand disease.
When crop residue levels are high, direct seeding can give wheat seedlings a better start. Direct seeding avoids the marked temporary nitrogen deficiency in conventional tillage fields caused by incorporating large amounts of straw into the soil.
Early seeding of wheat into a heavily strawed field might result in more severe frost injury to the crop, but such injury is no more damaging to wheat establishment than sunscald on emerging wheat in tilled soil. Wheat may take one to three more days to emerge on direct seeded fields due to cooler soil conditions in some years.
