Winter Wheat Performance Following One-time High Rates of Compost and Annual Cover Crop Planting in Wheat-fallow Rotations

Aims: One-time high rates of compost were applied at 15, 30, and 45 Mg ha-1 to improve soil organic matter (SOM) and fertility in dryland organic winter wheat-fallow rotations. Cover crop mixtures (oats and Austrian winter peas) were planted in fallow phases annually to suppress weeds and reduce repetitive tillage used for weed control because the latter breaks down SOM.

Study Design: The experiment was laid-out in a split-plot design with four replications. Fertilizer (compost rates, inorganic fertilizer and no amendment control) and cover crops served as main and sub-plot factors respectively.

Place and Duration of Study: The experiment was conducted at the Sustainable Agriculture Research and Extension Center, University of Wyoming, from September 2015 to August 2018.

Methodology: Soil samples, weed biomass, wheat yield and protein quality data were collected and analyzed over three years.

Results: Results indicated that 45 Mg ha-1 compost increased (P=.05) soil total carbon (TC) and nitrogen (TN) concentrations up to 25 and 19% respectively, in the last two years. Wheat yield was not affected (p>0.05) by compost or cover crops in any growing season but 45 Mg ha-1 compost increased (P=.05) protein quality by 2-9% in the first growing season. Cover crops suppressed weeds while growing in the first growing season but had varying effects on weeds in wheat phases that followed them in rotation. It was noted that soil electrical conductivity levels affected by 45 Mg ha-1 compost was 5 times lower than wheat thresholds; and soil moisture loss by cover crops did not affect wheat yield.

Conclusion: 45 Mg ha-1 compost improves soil fertility and SOM in the short term. However, significant reflection of soil changes in wheat yield may take longer time. Further research is needed to effectively integrate cover crops as a weed control measure in dryland organic wheat-fallow rotations.