Minimum and delayed conservation tillage for wheat-fallow farming

Maintaining crop residue, clods, and roughness on the soil surface during summer fallow is critical for wind erosion control in the low-precipitation (< 300 mm annual) dryland wheat (Triticum aestivum L.) production region of the inland Pacific Northwest, USA. Conventional farming practices are intensive, involving eight or more tillage operations during the fallow cycle. My objective was to evaluate fallow conservation tillage management systems for soil water storage, residue retention, surface and subsurface soil cloddiness, surface roughness, wheat stand establishment, and grain yield during 6 yr at Lind, WA. The soil is a Shano silt loam (coarse-silty, mixed, superactive, mesic Xeric Haplocambids). Treatments were (i) conventional (tillage), (ii) minimum (herbicides and tillage), and (iii) delayed minimum (herbicides and delayed tillage). Averaged over years, precipitation storage efficiency in the soil was 51, 54, and 57% over winter, and 24, 26, and 26% at the end of the fallow cycle, for conventional tillage (CT), minimum tillage (MT), and delayed minimum tillage (DMT), respectively. Surface residue and surface clod mass were consistently reduced by 45% or more in CT compared with MT and DMT. There were no differences among treatments in seed-zone water content at time of sowing in September nor in grain yield in any year or when averaged across years. Results show that the longterm practice of minimum and delayed minimum tillage during fallow significantly increased surface residue and clod retention for erosion control with no adverse agronomic affects compared with conventional tillage.