Decomposition of wheat and barley straw treated with urea-sulfuric acid

Wheat straw treated with 0.5 or 1.0 ml/g urea-sulfuric acid (1 : 1 acid in water v/v) and incubated in Protneuf or Woodburn silt loam soils in the laboratory decomposed faster than nontreated straw the first 4-6 weeks but at 12 weeks the nontreated straw had decomposed 25% – 45% more. In a field experiment, urea-sulfuric acid treated straw, removed at 40-day intervals over 160 days, decomposed faster than nontreated straw. The differences were attributed to salt buildup in the laboratory samples, where electrical conductivities up to 17.6 dS/m were observed. In the field, leaching removed the excess salts. Nitrification produced up to 1875 mg NO3-N/kg Portneuf silt loam soil in the laboratory, indicating that nitrifying bacteria were not suppressed by the salt. Total plate counts with no straw were 1.8 x 10^6 microorganisms/g and with urea-sulfuric acid treated straw were 15.7 x 10^6/g soil after 14 days incubation. The respective actinomycete counts were 0.3 x 10^6 and 6.7 x 10^6/g for the no straw and straw-treated soils, respectively. The urea-sulfuric acid treatments suppressed straw decomposition in the laboratory and accelerated straw decomposition in the field