Evaluation of Fallow Methods Study: No-till, Reduced Tillage, & Traditional Fallow.

Water storage in the fallow year is a critical component of wheat-fallow production systems used in the Columbia Plateau region of Oregon, Washington and Idaho. Soil moisture is the yield limiting factor in low to intermediate rainfall zones, and timely stand establishment depends on being able to seed into stored seed-zone moisture. Three years of research compared water storage in four fallow systems: chemical fallow (CF), reduced tillage fallow (RTF) using an undercutter followed by herbicides, reduced tillage fallow using an undercutter followed by rodding (UR) and traditional  tillage fallow (TF) in an intermediate rainfall (12-14 inch) zone. The study examined seed-zone moisture conditions and overall impact to soil moisture storage. Measurements of crop residue levels were taken following planting. Yield data was collected. Three years of soil water data showed CF averaged less water in the top 0.3 m and more at 1.2 to 1.5 m than the other three treatments.  Total water in the 1.5 m profile showed no significant differences. Seed-zone moisture data demonstrated differences in gravimetric water content between 0.05 and 0.10 m depths that varied from year to year. The differences were smaller and less statistically significant when the sampling depths were corrected for bulk density. Crop residue levels were found to be significantly different with CF being the highest, followed by RTF and TF. Yield data has been collected for two years on TF, CF, and RTF. The TF treatment had a significantly higher yield than CF and RTF. There were not significant differences in yield between CF and RTF. In summary, amount of soil moisture and its placement in the profile appeared to be the most critical factor. RTF and CF provided higher surface residue levels, but yields were reduced under these systems. Yield advantage was due to earlier stand establishment under TF.