LONG-TERM TILLAGE AND CROP-ROTATION EFFECTS ON WINTER-WHEAT PRODUCTION IN NORTHERN IDAHO

Reduced tillage practices designed to control soil loss in the Palouse region of northern Idaho may adversely affect soil physical properties and decrease yields. The objective of this study was to determine the effects of long-term tillage and rotation practices on wheat (Triticum aestivum L.) yields following 10 yr of continuous management. Yields were obtained from 1984 to 1987 on a long-term tillage rotation experiment established in 1974 near Moscow, ID. Tillage treatments included conventional (CONV, moldboard plow), minimum (MIN, chisel), and no-tillage (NT). Crop rotations were a 2-yr winter wheat-spring pea (Pisum sativum L.) (WW-SP) rotation and a 3-yr winter wheat-spring barley (Hordeum vulgare L.)-spring pea (WW-SB-SP) rotation. Yields of the MIN and NT treatments averaged over the 4-yr period were 92 and 78% of the CONV treatment. Differences between yields were significant (P < 0.05). No-till yields were significantly less (P < 0.05) than both the CONV and MIN treatments during all years, whereas MIN and CONV yields were not significantly different during 1986 and 1987. Wheat grown under the WW-SB-SP rotation yielded significantly greater (P < 0.05) than the WW-SP rotation. Profile water extraction and N uptake were reduced in the MIN and NT treatments. The apparent decrease in root function may have resulted from higher surface layer impedance, or possibly, greater root disease pressure under MIN and NT management. Results indicate that winter wheat production under continuous no-till management in the Palouse region may not be feasible without substantial yield reductions. A reduced tillage system that utilizes some limited tillage appears to be a viable management alternative to conventional practices.