Reflectances from Four Wheat Residue Cover Densities as Influenced by Three Soil Backgrounds

Abstract It is important to know quantity of crop residue on the soil surface to maintain or to improve soil physical and chemical properties and to assess the soil's susceptibility to erosion. Our objective was to use remote sensing techniques to examine the potential for remotely differentiating among wheat residue quantities and bare soils. We used three soils of the northern Great Plains (Williams loam fineloamy, mixed Typic Argiboroll, Vanda Clay fine‐silty, mixed calcareous, frigid Ustic Torriorthents, and Lambert silt loam finesilty, mixed calcareous, frigid Typic Ustorthents) that had either dry or wet surfaces and 0, 33, 66, and 100% wheat residue covering the soil surfaces. A portable spectroradiometer, and a hand‐held four‐band radiometer were used to measure spectral response and an infrared thermometer to measure surface temperatures. The infrared thermometer results allowed for differentiation among wet and dry surfaces and among residue quantities when the soil background was wet. Temperature differences between wet and dry surfaces became smaller as residue quantities increased and were near the same at 100% cover. Data obtained from the two radiometers were similar. Based on the type of measurements made in our study and indices calculated, the conclusions are that remotely sensed temperatures may be useful to assess surface soil residue covers when all soil backgrounds are wet. Linear combinations of n spectral bands in n‐dimensional space were calculated to form spectral indices, referred to as n‐space indices. The first n‐space index probably holds the best promise for developing any type of relationship to determine amount of residue cover on an otherwise bare soil surface, albeit, it appears from the data that the usefulness of such a relationship would be limited to soils that are naturally dark colored or that are darkened by the effect of water.