Our research focused on the study of the physiological responses of maize hybrids and the evolution of yield as a result of the climatic factors of the production site, as well as basal and top-dressing. We focused on studying the relationship between chlorophyll content measurements (SPAD value) and nitrogen content to determine the amount of N-fertilizer recommended in precision maize cultivation and its timely application, contributing to increasing N-fertilizer efficiency, yield forecasting, and fertilizer application consultancy, as well as to determine maize drought stress by stomatal conductance analysis, which can help develop a cost-effective irrigation plan.

Our experiments were performed at the Experiment Site of the University of Debrecen, on calcareous chernozem soil, in a small plot experiment in 2019, involving Renfor (FAO 320) and Fornad (FAO 420) hybrids. In addition to the treatment without fertilization, the doses of 60 and 120 kg N ha-1 applied as spring basic fertilizer were followed by double top dressing in the V6 and V12 phenophases. The applied amounts were +30 kg N ha-1 in each phase.

As the phenological phases progressed, the stomas of the plants became more and more closed, and their stomatal conductance decreased. Hybrids responded differently to environmental stressors. The Renfor (FAO 320) hybrid had the highest conductance in the V6150 treatment of the V8 phenophase (669 mmol/m2-s). The stomata were more open due to high turgor pressure, i.e. crops could evaporate properly. Crops were in the worst physiological condition in the V14 phenological stage, i.e. at the appearance of the last leaf (224 mmol/m2-s) in the 120 kg N ha-1 basal dose (A120) treatment. Even the value measured in the V10 phenophase showed that the stomas closed due to the self-regulatory system of the plant. After the measurement, it would have been necessary to apply irrigation water. The hybrid Fornad (FAO 420) showed the highest conductivity in the V8 phenophase (630 mmol/m2-s), in the 90 kg N ha-1 treatment (V690), while the lowest (183 mmol/m2-s) in the R1 phenophase, in the 60 kg N ha-1 basal treatment (A60). In this case, the phenological stage V8 would have been appropriate for the application of irrigation water, since the stomata began to close after this point due to the decrease in the water supply. These findings support the conclusion that water stress can be detected early on by measuring the stomatical conductivity.

The chlorophyll SPAD value of maize hybrids was also a good indicator of the decrease in N nutrient uptake between the V12 and R1 phenological stages caused by limited water supply. The N nutrient uptake of the longer maturity hybrid Fornad (FAO 420) was slower than that of the shorter maturity hybrid Renfor (FAO 320).

Basal and top dressing affected the yield of hybrids in different ways. For the longer maturity hybrid Fornad (FAO 420), the early +30 kg N ha-1 top-dressing (V6150; P <0.05) was applied in addition to the 120 kg N ha-1 basal dose (A120), while for the shorter maturity hybrid Renfor (FAO 320), the A120 treatment (P<0.05) resulted in the highest yield. The yield advantage of the Fornad (FAO 420) maize hybrid was significant over the Renfor (FAO 320) maize hybrid in all treatments.

Our results are based on one year of measurement results, i.e. we had to draw cautious conclusions. Scientific research needs to be continued to obtain an even more accurate picture of the physiological responses of maize hybrids to climatic factors.

Keywords: basal and top dressing, SPAD readings, stomatal condunctance, plant stress