Abstract:The aim of this study was to develop a time-specific and time-critical method to overcome the limitations of traditional field sampling methods for variable rate fertilization.Farmers,agricultural managers and grain processing enterprises are interested in measuring and assessing soil and crop status in order to apply optimum amount of fertilizers.Field experiments were conducted during 2005-2006 at the Xiaotangshan Precision Agriculture Experimental Base,Changping District,Beijing(40°18′29″ N to 40°18′32″ N,116°44′02″ E to 116°44′22″ E).SPAD readings of winter wheat in the variable-rate plots were measured at Feek 5 growth stage in 2005,in order to decide the additional N rate to apply.The uniform rate fertilizer management was chosen as the CK.The SPAD readings of the first and second fully expanded leaf collected at different growth stages were compared between variable-rate treatment and CK,and the results showed that variable rate treatment could provide adequate nitrogen for winter wheat.The grain yield and protein content were measured among the CK and variable rate fertilizer treatments.Geostatistical analysis(ArcGIS10.0) was carried out to examine within-field spatial variability and the contour maps of yield and grain content.It indicated that variable rate treatments reduced the spatial variability of wheat yield and grain protein content.