Evaluating spectral indices for determining conservation and conventional tillage systems in a vetch-wheat rotation

Conservation tillage (CT) systems, which consist of reduced and no-tillage systems, retain considerable quantities of crop residues on the soil surface. These crop residues perform as a barrier to wind and water to decrease soil erosion and evaporation. The use of remote sensing technology provides fast, objective and effective tool for estimating and measuring any agricultural event. The challenge is to differentiate the tillage systems by the crop residue cover on the soil surface. Spectrally derived normalized difference tillage index (NDTI), Shortwave infrared normalized difference residue index (SINDRI), cellulose absorption index (CAI) and Lignin-cellulose absorption index (LCA) were examined to distinguish their value as remote sensing methods for identifying crop residue cover in conventional and conservation tillage systems. Tillage treatments included conventional tillage (MD: Mouldboard plow+Disk harrow), reduced tillage (CD: Chisel plow+Disk harrow), minimum till (MT: Stubble cultivator), and no-tillage (NT1 and NT2: with standing stubble and standing stubble plus threshing residue, respectively). CAI had a linear relationship with crop residue cover, which the comparative intensity of cellulose and lignin absorption features near 2100 nm can be measure by it. Coefficients of determination (r2) for crop residue cover as a function of CAI and LCA were 0.89 and 0.79 respectively. Absorption specifications near 2.1 and 2.3 µm in the reflectance spectra of crop residues in minimum and no- tillage systems were related to cellulose and lignin. These specifications were not evident in the spectra of conventional tillage system. In this study the best index to use was CAI, which showed complete separation tillage systems, followed by LCA and NDTI. Four tillage intensity classes, corresponding to intensive (<6% residue cover), reduced (10–20% cover) minimum (25–40%) and no-tillage (>60% cover) tillage, were recognized in this study