Tillering and nitrogen economy of low-density maize crops

For the maize (Zea mays L.) crop, tillering is promoted in resource-abundant seasons (e.g., rainfalls, nutrient availability) at low plant densities. For this crop husbandry, farmers rarely use nitrogen (N) fertilization. Particularly, the impact of tillering on N economy processes and the effects of N availability on grain yield generation of tillered maize crops have yet to be studied. (i) To compare the evolution of biomass and N uptake for tillered and de-tillered (manually removed) maize crops, and (ii) to evaluate the impact of tillers on nitrogen internal efficiency for biomass (NIEB), grain yield (NIEG), harvest index (HI) and N harvest index (NHI). Two irrigated field experiments in different cropping seasons (2017–2018 and 2018–2019) with a tillering-prone maize hybrid were conducted in Buenos Aires, Argentina. Treatments were a combination of plant density [3 levels, 4 pl m−2 = D4; 2 pl m−2 = D2, including an additional tiller removal treatment during the whole tillering window at D2, D2(-T)] and two soil N availabilities [unfertilized= 60 kg N ha−1 of native soil N (N-) and fertilized= 220 kg N ha−1 of native soil + applied N (N+)]. Biomass accumulation, N uptake, HI, NHI, grain N concentration (GrainN%), NIEB and NIEG were analyzed at the shoot (main shoot and tillers) and crop levels. At D2 with N+, tillered crops had greater biomass and N uptake than non-tillered crops but did not compensate for the density reduction compared to D4. NIEB of tillers was similar to that of main shoots, but HI, NIEG and NHI of tillers were lower than those of main shoots. A negative relationship between crop NIEG and GrainN% was sustained for main shoots, but not for tillers due to the low and variable HI of these secondary shoots. In low-density maize management scenarios, tillers increase resource capture in resource-abundant seasons, generating greater crop biomass through a sustained NIEB. However, an intrinsic lower HI of tillers (and NIEG) versus main shoots decreases NIEG of tillered crops. Knowledge gaps regarding the impact of tillers on N economy of maize crops were answered for the first time. New issues arise: to compare the N dilution curves for main shoots and tillers and to quantify post-flowering N uptake of tillers and N remobilization from tillers to main shoots.