Crop residue position and interference with wheat seedling development

Unweathered crop residues can produce growth-inhibiting substances, stimulate pathogen growth, and immobilize nutrients. The location of seed relative to residue may be an important factor in the early health of a crop. This greenhouse study simulated sowing conditions possible under annual dryland winter wheat (Triticum aestivum L.) production to evaluate the likelihood of inhibitory effects. We placed newly harvested, unweathered winter wheat residue on the soil surface, mixed with the seed, immediately above the seed, or 3 cm below the seed. Treatments using a plastic residue substitute and treatments using pasteurized soil and residue provided comparisons to the natural soil and wheat residue. Residue mixed with or placed above the seed caused a temporary delay in emergence. Since this occurred with both wheat and plastic residue, the delay is explained by the physical impedance of coleoptile growth. Wheat residue 3 cm below the seed reduced the height and rate of wheat plant development, indicating a biological inhibitory effect of the wheat residue. This reduction in height and development rate at 20 days after planting did not occur when the soil and residue were pasteurized. We conclude that winter wheat seedling growth can be inhibited if roots encounter unweathered residues.