Characterization of Cereal Crop Residue in Conservation Farming Systems.

Residue management is a major concern for growers who wish to practice minimum- or no-tillage farming in the dryland farming region of the Pacific Northwest.  In higher rainfall zones, abundant cereal residue inhibits no-till seeding on steeply sloping land; conversely in lower rainfall zones too little residue may exist to conserve precious soil moisture or to combat wind erosion.  Residue from cereal crops and cultivars varies in fiber and nutrient content, and thus in decomposition potential.  The objective of this research was to characterize the winter wheat and spring barley cultivars currently grown in the region, as well as some experimental cultivars, for their fiber and nutrient content.  Using traditional wet-chemistry and combustion methods, we found that cultivars varied in their neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), ash (AIA), carbon (C), and nitrogen (N) content, and thus hemicellulose and cellulose content.  Acid detergent lignin was highest in spring barley residue, followed by hard winter wheat and soft white winter wheat.  Soft white winter wheat had higher hemicellulose and cellulose than hard winter wheat and spring barley.  Spring barley residue NDF, ADF and ADL were lower in areas of lower annual precipitation.  Winter wheat residue did not follow that same trend for NDF, ADF or ADL.  Straw from lower rainfall zones had the lowest AIA.  Near-infrared spectroscopy (NIRS) shows promise as a method to reduce the time, labor, and chemicals needed to characterize residue through traditional methods.  NIRS was able to accurately predict NDF and ADF of wheat and barley residue (R² > 0.90), and was moderately successful in predicting ADL content (R² = 0.81).  Information on differences in straw decomposition among wheat and barley cultivars will assist growers in selecting cultivars for reduced tillage systems.