Comparing Common Hyperspectral Vegetation Indices for Their Ability to Estimate Seasonal Nitrogen and Other Variables in Winter Wheat Across a Growing Season

Abstract Field spectroscopy was used to assess the nitrogen status and monitor crop growth and production of wheat (Triticum aestivum L, cv. Chara) under a range of nitrogen fertilizer treatments and two irrigation levels (rainfed and irrigated) throughout the growing season. The association between a range of commonly used vegetation indices for the detection of green biomass, nitrogen or chlorophyll concentration, and measured crop characteristics (nitrogen concentration, total nitrogen accumulated, dry weight, wet weight, relative foliar cover and moisture content) was determined for six moments in the growing season. At about 95–144 days after sowing, a strong correlation (r2 between 0.7 and 0.99, p<0.01) existed between vegetation indices and wheat biomass, relative foliar cover and total nitrogen load per square meter. However this association did not hold when multiple sample dates were combined. Changes in total biomass and/or foliar cover strongly affected the association between vegetation measures and the vegetation indices, making between-date comparisons difficult.