TILLAGE MULCH DEPTH EFFECTS DURING FALLOW ON WHEAT PRODUCTION AND WIND EROSION CONTROL FACTORS

Blowing dust from summer fellow is a major soil loss and air quality c oncern in winter wheat (Triticum aestivum L.) production areas of the inland Pacific Northwest (PNW). The objective of our 3-yr on-farm stud y in a 286-mm precipitation zone in eastern Washington was to determin e the effects of tillage mulch depth during fallow on surface soil rou ghness, residue retention, seed-zone water storage, wheat establishmen t, and grain yield. Soil is a Ritzville silt lo;un (coarse-silty, mixe d, mesic Calcidic Haploxeroll). Mulch depth combinations were created by primary spring tillage with noninversion implements at 100- or 160- mm depths, and with subsequent rodweedings at 50- or 100-mm depths. Ti llage mulch depth during fallow did not affect seedling emergence afte r two wet fallow cycles, but wheat spike density was consistently grea test in deep-tilled plots. In a dry fallow cycle, when dry soil extend ed beneath the rodweeder or secondary tillage layer, deep tillage incr eased stand establishment from 30 to 62 seedlings m(-2), grain yield f rom 4.4 to 5.3 Mg ha(-1), and residue production from 5.7 to 8.4 Mg ha (-1) compared with shallow tillage. Surface soil clods >50-mm diameter , desirable for wind erosion control, increased with tillage mulch dep th from 14 to 21 Mg ha(-1) in 1994, and from 22 to 37 Mg ha(-1) in 199 5. A drawback to deep tillage mulches was the need to reduce tractor s peed during planting. Surface residue retention was not affected by ti llage mulch depth. Results show that surface clod structure and roughn ess during fallow can be maintained to protect the soil from erosion, mostly benefiting wheat production potential.