The effect of nitrogen fertilization on flag leaf and ear photosynthesis and grain yield of spring wheat

In a three-year field experiment the assessment of leaves and ears photosynthesis rate in spring wheat was made using a LI-COR 6400 portable photosynthesis system. The photosynthetic rate of spring wheat was affected by cultivars, nitrogen fertilization and weather conditions. We generally found a negative correlation between the yield of spring wheat and the rate of photosynthesis in flag leaves in phases 39-55 BBCH (the strength of this effect depended on the level of nitrogen fertilization). Strong negative correlation occurred for cv. Bryza in phases: 39-51 BBCH in treatment fertilized with lower dose of nitrogen and in phase 39-41 BBCH for dose 120 kg/ha. There was a significant negative correlation for cv. Tybald only in phase 39-41 BBCH for higher dose of nitrogen and 52-55 BBCH for lower dose. Our studies show that the photosynthetic activity of flag leaves decreased from the booting (39-41 BBCH) to heading stage (52-55 BBCH), and their function was taken over by ears. Contrary to flag leaf, in wheat ears the intensity of photosynthesis correlated positively with grain yield for most of the studied period (52-65 BBCH, with highly significant correlation at 56-57 BBCH and - only for high nitrogen treatments - at 59-61 BBCH; a negative correlation was generally observed at a later phase, i.e. at 65-69 BBCH). Contrary to flag leaf photosynthesis, the intensity of this process in wheat ears (at the heading and flowering stages) seems highly relevant for grain yield. High positive correlation was noted in 56-57 BBCH and 61-65 BBCH. However, the study was done in field conditions and for definitive conclusions observations over a longer period would be desirable.