Radiative and Conductive Transport of Heat through Flail-Chopped Corn Residue

We know of no experiments on thermal radiation (3–100 µm) and sensible heat transfer in crop residues, although data are needed to model the energy balance of conservation tillage systems. The objective of this study was to develop methods for measuring the transmittance of thermal radiation in crop residues and the thermal conductance of the residue, and then to use the measurements to test a model of radiation and sensible heat flow in a crop residue. The extinction coefficient for thermal radiation through uniformly distributed, flail-chopped corn (Zea mays L.) residue was measured as 1.57, which is more than 50% greater than that expected for black, randomly distributed, horizontal residue pieces (1.0). We believe the larger extinction coefficient resulted because the residue pieces were distributed more nearly uniformly than randomly. This indicates the need to measure extinction coefficients for different kinds of residue, since the residue pieces usually are not spread randomly. The total heat flux densities (radiation plus sensible heat) through residues with areal densities of 0.95 and 0.48 kg m⁻² were measured under thermally stable and unstable conditions. Buoyancy-driven convection was suppressed in the residue. The calculated sensible heat conductivity of flail-chopped corn residue was only 2% greater than still air. Even with 0.95 kg m⁻² of residue and a large extinction coefficient, thermal radiation contributed over 60% of the total heat flow. Modeled total heat flows ranged from 0.91 to 1.15 times measured flows. We believe the disagreement between measured and modeled values resulted from differences in radiation transfer caused by small differences in residue element packing. Research supported by the College of Agric. and Life Sci., Hatch Formula funds (Project 142-2888), and USDA Specific Cooperative Agreement 58-5759-5-3.