Tillage Mulch Depth Effects during Fallow on Wheat Production and Wind Erosion Control Factors

Blowing dust from summer fallow is a major soil loss and air quality concern in winter wheat (Triricum aesrivum L.) production areas of the inland Pacific Northwest (PNW). The objective of our 3-yr onfarm study in a 286-mm precipitation zone in eastern Washington was to determine the effects of tillage mulch depth during fallow on surface soil roughness, residue retention, seed-zone water storage, wheat establishment, and grain yield. Soil is a Ritzville silt loam (coarse-silty, mixed, mesic Calcidic Haploxeroll). Mulch depth combinations were created by primary spring tillage with noninversion implements at 100or 160-mm depths, and with subsequent rodweedings at 50or 100-mm depths. Tillage mulch depth during fallow did not affect seedling emergence after two wet fallow cycles, but wheat spike density was consistently greatest in deep-tilled plots. In a dry fallow cycle, when dry soil extended beneath the rodweeder or secondary tillage layer, deep tillage increased stand establishment from 30 to 62 seedlings m-l, grain yield from 4.4 to 5.3 Mg ha-', and residue production from 5.7 to 8.4 Mg ha-l compared with shallow tillage. Surface soil clods >SO-mm diameter, desirable for wind erosion control, increased with tillage mulch depth from 14 to 21 Mg ha-' in 1994, and from 22 to 37 Mg ha-' in 1995. A drawback to deep tillage mulches was the need to reduce tractor speed during planting. Surface residue retention was not affected by tillage mulch depth. Results show that surface clod structure and roughness during fallow can be maintained to protect the soil from erosion, mostly benefiting wheat production po-