Wheat Residue Loss for Chemical and Stubble‐mulch Fallow

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Abstract
Surface placement of wheat (Triticum aestivum L.) residue can be an effective practical method for erosion control in the semiarid Plains. Therefore, a study was conducted to determine the effect of chemical and stubble‐mulch fallow on residue orientation and decomposition, N and P concentrations, C/N ratios, and to compare straw weight per unit length and stalk population of standing winter wheat residue on chemical fallow plots to that of spring wheat. the study was conducted on a Williams loam (fine‐loamy, mixed Typic Argiborolls) in eastern Montana. Chemical fallow plots were sprayed four times, whereas stubble‐mulch fallow plots were tilled with sweeps, followed by three additional tillage operations with a rod weeder to control weeds. Residue samples were collected and analyzed periodically during 426‐d (14 months) winter wheat fallow and 638‐d (21 months) spring wheat fallow periods. Quantities of winter and spring wheat surface residue on stubble mulch plots decreased 70% from May through July of the year following harvest, while on chemical fallow plots, standing residue decreased and flat residue increased at constant rates. Chemical fallow plots had three times more surface residue for erosion control after 426‐ and 638‐d of fallow than stubble‐mulch fallow plots. About 27 and 8% of the initial winter and spring wheat total residue, respectively, were standing at the end of fallow on chemically fallowed plots. Nitrogen concentration was about 1.3 times greater, and P concentration two times greater for flat residue, than for standing residue.