Liquid N and S Fertilizer Solutions Effects on the Mass, Chemical, and Shear Strength Properties of Winter Wheat (Triticum aestivum) Residue

Abstract

Abstract. To improve stand establishment in high crop residue situations, the utility of fertilizer to stimulate microbial decomposition of residue has been debated. Field experiments assessed winter wheat () straw decomposition under different fertilizer rates and application timings at three sites in western Kansas following wheat harvest in 2011 and 2012. Treatments included urea ammonium nitrate (UAN) applied at rates of 0, 22.4, 44.8, or 67.2 kg N ha-1 and ammonium thiosulfate (ATS) applied at rates of 16.8 or 33.6 kg S ha-1. Residue was collected and characterized for physical and chemical parameters. A double shear box apparatus instrumented with a load cell measured the energy required to cut wheat straw. Photomicrography and image analysis software were used to measure the cross-sectional area of each individual wheat straw after shearing, and these data were used to calculate shear stress and specific energy parameters. Total C and N contents were measured for bulk wheat straw samples from each plot. Some differences among treatments or timing of application were observed for each of the measured parameters. However, the results were inconsistent, and few sampling periods had significant differences in wheat straw decomposition indicators as compared to the no-fertilizer control. For example, fertilizer rate and timing of application during summer 2012 and fall 2013 at the Hays site had impacts on wheat straw shear stress at the break point. Across site years, earlier (fall) fertilizer application generally resulted in lower remaining residue mass as compared to spring application. However, there were no differences when compared to the no-fertilizer control. Multivariate and linear regressions suggested that N content and C:N ratio could explain the results observed with respect to treatment effects on winter wheat residue decomposition. Keywords: Liquid fertilizer, Residue decomposition, Shear stress, Specific energy.