Residue Type and Placement Effects on Decomposition: Field Study and Model Evaluation

Abstract

Decomposition of corn (Zea mays L.), soybean (Glycine max [L.] Merr.), wheat (Triticum aestivum L.), grain sorghum (Sorghum bicolor [L.] Moench), and cotton (Gossypium hirsutum L.) residues and dead roots was studied under field conditions at the Midwest Claypan Experimental Farm located near Kingdom City, Missouri. Residues in fiberglass bags were placed on the soil surface and 0.15 m above and below the surface of a Mexico silt loam (Udollic Ochraqualf). Root bags were also buried 0.15 m below the surface. Samples were collected 11 times during the two-year study. Mass losses in one year for above-surface, surface, buried residue, and dead root were 41, 66, 78, and 65%, respectively, for corn; 37, 66, 79, and 51% for soybean; 17, 36, 69, and 64% for wheat; 45, 66, 80, and 76% for grain sorghum; and 40, 58, 76, and 46% for cotton. Decomposition was relatively slow during the second year of the study because of the previous loss of easily decomposed compounds. Decomposition data were used to evaluate a theoretically derived residue decay model. Relationships between predicted and measured mass loss were linear with r2 values > 0.93.