2ND-DERIVATIVE SPECTRA FOR ESTIMATING CROP RESIDUE COVER

Estimating crop residue is important for soil conservation and tillage management, and such estimates are used in determining conservation c ompliance with the U.S. Food Security Act of 1985. This study was cond ucted to (i)examine the relationship between derivative spectra of ref lectance and oat (Avena sativa L.) residue covers and (ii) determine i f the relation can be used to estimate oat residue cover from ground-b ased reflectance measurements, using broad-band (MMR) and high-spectra l-resolution (SE590) instruments. A simple spectral model was proposed to interpret the interaction of solar radiation and crop residue with different soil backgrounds. A spectral derivative technique was appli ed to the field-measured reflectance data to minimize the soil backgro und noise and extract information about crop residue. SE590 wavelength at 402 nm and MMR Band 1 (450-520 rum) were the most sensitive. The s econd-derivative value, defined as the derivative spectral index, stro ngly correlated (r2 greater-than-or-equal-to 0.85) with oat residue co ver using SE590 and MMR data. Four empirical regression equations were developed from the relationship between the derivative spectral index and the oat residue cover from four different data sets. Our results suggest that derivative spectral indices can be useful for estimating fresh oat residue in a disked field. The broad-band data also can be u sed to calculate the derivative spectral index for detecting oat resid ue.