Small-Scale Variation in Nitrogen Use Efficiency Parameters in Winter Wheat as Affected by N Fertilization and Tillage Intensity

Limited information exists on how tillage and nitrogen (N) fertilization affects small-scale variation in nitrogen use efficiency (NUE) and crop performance. In a two-year field study under temperate conditions, we investigated how tillage (NT, no-tillage; CT, conventional tillage) and N fertilization affected the small-scale variation in NUE and winter wheat performance (grain yield, G w ; grain protein concentration, GPC). A randomized complete block design with three replications was used. Within each tillage plot (12 × 35 m 2 ), N rates (0, 50, 100, 150, 200, 250 kg N ha −1 ) were completely randomized within each of four groups of microplots (1.5 × 1.5 m 2 ). Early-season soil mineral N (N min ) was also monitored in both years. At rates < 150 kg N ha −1 , NT was not competitive with CT in terms of G w and NUE. G w and aboveground plant N were not correlated with N min prior to application of N fertilizer. NT usually led to larger spatial heterogeneity of N min , G w , and NUE. The small-scale variability of G w , GPC, NUE, and N supply decreased with increasing N fertilization rates under both tillage systems. Significant increases in G w and GPC were observed with increasing N rates, whereas NUE decreased slightly with increasing N rates in both NT and CT. The overall moderate spatial variation in N min , G w , and NUE did not justify site-specific N fertilization in these small fields, with the exception of the stony within-plot positions, which were not responsive to rates of N > 50 kg N ha −1 .