Remote sensing of biomass and yield of winter wheat under different nitrogen supplies

Vegetation indices derived from reflectance data are related to canopy vari ables such as aboveground biomass, leaf area index (LAY), and the fraction of intercepted photosynthetically active radiation (fIPAR). However, under N stress the relationships between vegetation indices (VI) and these canopy variables might be confounded due to plant chlorosis. We studied the relat ionships between reflectance-based VI and canopy variables (aboveground bio mass, LAP canopy chlorophyll A content [LAI X Chi A], and fIPAR) for a whea t (Triticum aestivum L.) crop growing under different N supplies. Nitrogen fertilization promoted significant increases in radiation interception (pla nt growth) and, to a lesser extent, in radiation use efficiency (RUE). The VI vs. LAI relationships varied significantly among treatments, rendering t he VP-based equations unreliable to estimate LAP under contrasting N condit ions. However, a single relationship emerged when LAI X Chi A was considere d. Moreover, VP were robust indicators of fIPAR by green canopy components independently of N treatment and phenology. Aboveground biomass was poorly correlated with gain yield, whereas cumulative VP simple radio (SR) was a g ood predictor of grain yield, probably because cumulative SR closely tracke d the duration and intensity of the canopy photosynthetic capacity.