Abstract: A field plot experiment was conducted to measure the canopy spectral r eflectance and aboveground fresh biomass of four spring wheat varieties (Dingxi 24, Longchun 8139, Gaoyuan 602 and Dingxi 38) at their different growth stages a nd under different planting densities. The variations of the aboveground fresh b iomass with growth stages as well as the correlations of the aboveground fresh b iomass with canopy reflective spectrum and first derivative spectrum were analyz ed, and based on these, hyperspectral remote sensing estimation models for sprin g wheat aboveground fresh biomass were established, with the characteristic band s and their combinations strongly correlated with the aboveground fresh biomass as the variables. The tests with experimental data showed that models y=3 9498 ln F780+70596 and y=51299 D71910174 had the h ighest estimation level, with the root mean square error, relative error, and co rrelation coefficient between estimated and measured values being 02173, 104 5% and 0854, and 02188, 996%, and 0853, respectively. These two models c ould be used as the best models for the estimation of spring wheat aboveground f resh biomass on Longzhong Loess Plateau.

Key words: N₂O, Emission factor, Agricultural field, Precipitation