Apparent fertilizer N recovery and the relationship between grain yield and grain protein concentration of different winter wheat varieties in a long-term field trial

A high recovery of applied fertilizer nitrogen (N) is required to minimize the environmental impact and to achieve high grain protein concentrations (GPC). Based on a long-term field trial (1976-2018) with winter wheat in northern Germany with 64 N fertilizer treatments differing in amount (0-360 kg N ha(-1)) and distribution, the effects of N fertilizer amount and variety on the apparent fertilizer N recovery (AFR) of three application dates were determined. In addition, the relationship between grain yield (GY) and GPC was analyzed. Apparent fertilizer N recovery was lowest for N applied at the beginning of spring growth (N1), but highest if applied at ear emergence (N3). It decreased with increasing N amounts. Newer varieties, cvs. Tommi and Julius (released in 2002 or 2008), achieved higher AFR than those released in 1993 and earlier (cvs. Diplomat, Kanzler, Orestis, Ritmo), especially that of late-season N due to both increased GY and GPC. When estimating the correlation between GY and GPC and the effect of N3 on it, the amount of N fertilization applied before ear emergence (sum of N applied at the beginning of spring growth (N1) and N applied at the beginning of stem elongation (N2)) has to be taken into account, because N1 + N2 affects the source size of N which can remobilized and translocated into the grain. For the older varieties, a negative linear correlation between GY and GPC was found; however, in the treatments with N1 + N2 = 120, 160 and 200 kg N ha(-1), the newer varieties responded differently with firstly a decrease in grain protein concentration with increasing grain yield, but then achieving a plateau, namely GPC remained stable with rising GY. Probably, this was due to a more pronounced post-anthesis N uptake.