OBTAINING MODELS FOR ALFALFA, SORGHUM, AND WHEAT RESIDUE DECOMPOSITION

Crop residues provide an economical means for controlling wind and water erosion in addition to being a valuable source of plant nutrients. As residues decompose they lose nutrients, mass and the ability to protect the soil surface from erosive forces. The research was designed to evaluate rates of residue decomposition of sorghum, wheat and alfalfa on the soil surface and buried, in five soil moisture regimes. Moisture was applied to soil by line source irrigation and bags containing crop residues were retrieved and analyzed across time. Thus, observations were repeated in both space and time . Wieder and Lang (1982) reported that mass-loss over time was modeled well by the negative exponential. Because residue can be divided into fast (labile) and slow (recalcitrant) decomposing fractions, the double exponential is suggested. Assuming the ratio of labile to recalcitrant is constant for. a crop regardless of soil moisture, and whether on the surface or buried, it would be sufficient for each crop to fit a set of simultaneous non-linear functions with three parameters, a constant A (proportion labile) over all equations with different k1,\u27s (labile fraction decomposition rates) and k 2\u27s (recalcitrant decomposition rates) for soil moisture levels and whether buried or unburied . For alfalfa the results were consistent with the above theory. For wheat and sorghum data holding A constant over all environments resulted in k\u27 s \u3e 0. Convergence of the estimations process could not be obtained when forcing k\u27s ≤ 0. The single exponential provided a satisfactory model of decomposition, but without the advantage of separating the residues into labile and recalcitrant fractions. The inability to obtain estimates using the double exponential apparently resulted from an insufficient observation period. The recalcitrant fraction of the surface residues of these crops had not disappeared after more than a year