Evaluation of Physical Strength of Wheat Straw Under Different Fertilizer Treatments and Rates.

Application of nitrogen (N) fertilizer as urea ammonium nitrate (UAN) and N plus sulfur (S) fertilizer as ammonium thiosulfate (ATS) in a mist on crop residue to stimulate microbial activity and subsequent decomposition of the residue is often debated, particularly for its potential to solve stand establishment issues in high residue situations. We conducted wheat straw decomposition field experiments under different fertilizer rates and combinations at three locations in western Kansas following wheat harvest in 2011 and 2012. Liquid fertilizer was applied to the residue with a flat fan spray tip onto 37.2 square meter plots. Treatments were applied in November 2011 or February 2012 for the first experiment period and November 2012 or February 2013 for the second experiment period. Wheat straw was collected in July 2012 for the first experiment period and June and October 2013 for the second experiment period to determine residue mass and physical strength parameters. A double shear box apparatus instrumented with a load measured the shear stress required to cut wheat straw. Twenty-five wheat straws from each plot were tested. Photomicrography and SigmaScan software were used to measure the cross-sectional area of wheat straw after shearing. Total C and N were also analyzed. Results showed the fertilizer rate and timing of application during summer 2012 and October 2013 at the Hays site had impacts on wheat straw shear stress at break point. Earlier fertilizer application generally resulted in lower remaining aboveground biomass. Significant results were measured three times during the first two sampling period. Liquid fertilizers decreased wheat straw physical strength and lowered C content relative to the no-fertilizer control, thus indicating the possibility of potential benefits of liquid fertilizers to speed decomposition in heavy residue situations.