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Dep. of Crop and Soil Sciences
Dep. of Crop and Soil Sciences/Inst. of Ecology, Univ. of Georgia, Athens, GA 30602
*Corresponding author (mquemada{at}uga.cc.uga.edu).
ABSTRACT
Winter annual cover crops, widely used in no-till systems, can be an important source of N for the subsequent crop. Because many factors affect net N mineralization from cover crop residues, computer models can be powerful tools to predict it. The CERES models, which are some of the most widespread models for simulating the whole crop-soil system, have a common submodel (CERES-N) that describes N transformations. The objectives of this study were to determine decay rate constants under nonlimiting conditions for the carbohydrates and cellulose pools (CARB and CELL) of CERES-N for residues that decompose on the soil surface, and to test if two modifications to CERES-N could improve the simulation of N mineralization. The two modifications were to: (i) allow the user to vary the relative size of the residue pools (CARB, CELL, and lignin), and (ii) allow stems and leaves to decompose separately, having a common point of interaction through the inorganic N pool. Results of a 6-mo laboratory incubation experiment with four cover crop residues were used to adjust rate constants and test the effect of model modifications. The decay rates obtained were 0.14 and 0.0034 d–1 for CARB and CELL, respectively. Allowing the user to vary the relative size of residue pools greatly improved the simulation of net N mineralized (root mean square error of the model decreased from 1.0 to 0.28 g m–2), whereas modeling the separate decomposition of leaves and stems only caused a slight improvement in the prediction of net N mineralized.
Received for publication July 29, 1994.
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