Physiological constraints to realizing maize grain yield recovery with silking-stage nitrogen fertilizer applications

Understanding the physiological factors which allow or constrain maize (Zea mays L.) recovery from vegetative N stress when N fertilizer is added near flowering is important for N management decisions. To study the capacity of maize to recover from vegetative N stress, we conducted a two-year experiment comparing seven hybrids (released between 1946 and 2015) and five N treatments - a 0 N control (0_0) and four treatments which received a total of 220 kg N ha−1 applied either 100% at V4 (220_0), 100% at R1 (0_220), 75% at V4 and 25% at R1 (165_55), or 25% at V4 and 75% at R1 (55_165). These N treatments created a range of N deficiencies at flowering. There was no indication that yield response to the timing of N application had changed over the past 70 years of hybrid improvement. Compared to 220_0, grain yield was significantly lowered by the delayed application of 0_220 (relative yield of 89%) but not by the split applications of 55_165 or 165_55 (relative yields of 93 and 100%, respectively), although both 0_220 and 55_165 were under N stress at R1, as indicated by the N Nutrition Index. The reasons for the lower grain yield in 0_220, but not 55_165, appeared to be 1) low vegetative-stage N accumulation which could not be compensated for by increased post-silking N uptake, 2) lack of recovery of leaf N status following the R1 N application, and 3) significantly reduced biomass accumulation during the vegetative growth. These findings provide a better understanding of the ability of maize to recover from moderate early-season N stress and will aid agronomists in making management decisions regarding the timing of N fertilizer applications.