STEM SOLIDNESS AND LITTER QUALITY IMPACTS ON RESIDUE DECOMPOSITION AND RESIDUE COVER IN DRYLAND WINTER WHEAT

Abstract

Solid-stem wheat varieties have been widely adopted across the Great Plains as a management strategy for wheat stem sawfly (Cephus cinctus, Norton), yet their consequences for post-harvest residue decomposition and soil cover persistence remain poorly understood. This study evaluated whether stem solidness influences residue decomposition and residue cover persistence across a gradient of eight winter wheat varieties ranging from hollow to semi-solid, using a 134-day laboratory incubation, a 229-day field litterbag experiment, and residue cover monitoring across three site-years under dryland winter wheat production in Colorado. Neither laboratory-measured nor commercial solidness ratings significantly predicted decomposition responses in either study. Instead, fiber fractions, particularly amylase treated neutral detergent fiber (aNDF), acid detergent fiber (ADF), and hemicellulose, along with nitrogen (N) availability, indicated by total N and C:N ratio, were the dominant predictors of cumulative C mineralized, decay rate, final C remaining, and final mass remaining across both studies. In the litterbag study, variety-level differences in residue persistence were driven primarily by differences in early mass loss rather than overall decay rates. The relative ranking of varieties was consistent across the incubation and litterbag environments despite large differences in overall decomposition rate, suggesting that residue chemical composition is a robust driver of decomposition dynamics independent of environmental setting. Lignin-based indices were comparatively weak predictors, as was expected with the early decomposition stage captured here, where decomposition did not exceed the threshold at which lignin typically becomes the dominant control on decay rate. Residue cover across three site-years showed high stem solidness plots (solidness ratings 16,19) maintained significantly greater cover than medium solidness plots (solidness 10). Together, these findings indicate that fiber content and N availability are more reliable predictors of residue decomposition outcomes in dryland wheat systems than stem solidness, and that growers selecting solid-stem varieties for sawfly resistance need not expect large or consistent residue cover impacts from that selection.