Effects of Tillage Practices on Soil and Wheat Spectral Reflectances1

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Abstract
The objective of the study, which was located on a Williams loam soil (fine‐loamy, mixed Typic Argiborolls) near Sidney, Mont., was to attempt to discriminate by reflectance determinations among varying degrees of wheat (Triticum aestivumL.) stubble and crop growth covering the soil surface. Spring and winter wheat were seeded no‐till (NT) into standing spring wheat stubble and after one tillage operation on stubble‐mulch fallow and on bare soil. Also included in the study were bare fallow, stubble‐mulch fallow, and chemical fallow. A handheld radiometer With bandpass intervals similar to those of the multispectral scanner aboard Landsat was used to measure radiances from the plots. Reflectances were calculated as the ratio of plot radiance to the radiance from a barium sulfate plate. Reflectance differences among fallow treatments were not consistent throughout the season, and it is questionable whether, with present techniques, we can discern among fallow treatments. Wheat that was seeded NT into standing stubble and wheat that was seeded after one tillage operation could be detected and separated from soil readings as early as wheat seeded on bare fallow. Sparse crop growth during a drought year could not be separated from soil background. The relationship between green leaf dry matter (DM) and IR/Red ratio suggests that reflectance measurements may substitute for manual measurements of green leaf DM.

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