Effects of basal/topdressing nitrogen ratio on light interception and dry matter transport at different layers of wheat canopy under supplemental irrigation based on soil moisture

Objectives Under water-saving cultivation conditions, the effects of base application ratio of nitrogen on light energy utilization and accumulation, transport and distribution of dry matter in different layers of wheat canopy were studied to provide a basis for rational nitrogen fertilizer management.

Methods The study included five treatments at a nitrogen application rate of 240 kg/hm², with fertilizer ratios of base to topdressing of 0∶10 (N1), 3∶7 (N2), 5∶5 (N3), 7∶3 (N4) and 10∶0 (N5) for the cultivar Jimai 22. Relative soil moisture content was maintained up to 70% of field capacity at the joining and anthesis stages of wheat.

Results Leaf area index at 0, 7 and 14 days after anthesis, photosynthetically active radiation (PAR) capture ratios in upper and middle layers of wheat canopy under the N3 treatment with ratio of base fertilizer to topdressing of 5∶5 were significantly higher than those under other treatments, and penetration through the middle and lower wheat canopy layers was significantly lower than that under other treatments. Compared with the N1, N2, N4 and N5 treatments, PAR conversion and utilization efficiencies of N3 were increased by 13.64%, 8.02%, 8.70% and 14.38%, and 21.17%, 8.50%, 10.67% and 23.88%, respectively. Dry matter assimilation after anthesis, dry matter accumulation at maturity, rates of dry matter translocation and transport from middle-layer vegetative organs to grains before flowering under the N3 were significantly higher than those under other treatments. Compared with the N1, N2, N4 and N5 treatments, dry matter distribution amounts in grains at maturity were increased by 11.37%, 5.68%, 6.03% and 16.25%, respectively. Correlation analysis showed that dry matter transport from middle-layer vegetative organs to grains before flowering was significantly and positively correlated with PAR capture ratio in the middle layer. Dry matter distribution in grains was significantly and positively correlated with PAR capture ratios in the upper, middle and all layers, and significantly and negatively correlated with PAR capture ratio in the lower layer.

Conclusions The treatment with base to topdressing fertilizer ratio of 5:5 significantly enhanced light energy utilization in wheat canopy, promoted dry matter transport from middle-layer vegetative organs to grain before anthesis and accumulation of dry matter after anthesis, and resulted in the highest grain yield. The treatment with base to topdressing fertilizer ratio of 5:5 was the best treatment under the test conditions.