ESTIMATING CROP RESIDUE DECOMPOSITION FROM AIR-TEMPERATURE, INITIAL NITROGEN-CONTENT, AND RESIDUE PLACEMENT

Managing cereal residues to control soil erosion by wind and water requires knowledge of residue decomposition. Four equations were developed to estimate decomposition of cereal residues based on cumulative degree days (CDD) calculated from daily maximum and minimum air temperature. Each is based on the general equation Rr = Ir exp(fN fWk CDD), where Rr = residue remaining, Ir = initial residue, fN is an N coefficient based on initial residue N content, fW is a water coefficient based on a combination of residue and field management, and k is a general decomposition coefficient. Projected decomposition was tested against data for different varieties of soft white and hard red spring and winter wheat (Triticum aestivum L.), durum wheat (T. durum Desf.), spring and winter barley (Hordeum vulgare L.), triticale (x triticosecale Wittm.) corn (Zea mays L.), and soybean [Glycine max (L.) Merr.] from Alaska, Idaho, Indiana, Missouri, Oregon, Texas, and Washington. The mean slope of the line relating observed to projected decomposition for all locations was 1.10 +/- 0.543 with r2 values ranging from 0.76 to 0.99, with most > 0.95.