Optimizing plant density and nitrogen application to manipulate tiller growth and increase grain yield and...

The growth of wheat tillers and plant nitrogen-use efficiency (NUE) will gradually deteriorate in response to high plant density and over-application of N. Therefore, in this study, a 2-year field study was conducted with three levels of plant densities (75 ×10⁴plants ha^-1, D1; 300 ×10⁴plants ha^-1, D2; 525 ×10⁴plants ha^-1, D3) and three levels of N application rates (120 kg N ha^-1, N1; 240 kg N ha^-1, N2; 360 kg N ha^-1, N3) to determine how to optimize plant density and N application to regulate tiller growth and to assess the contribution of such measures to enhancing grain yield (GY) and NUE. The results indicated that an increase in plant density significantly increased the number of superior tillers and the number of spikes per m²(SN), resulting in a higher GY and higher partial factor productivity of applied N (PFP_N). However, there was no significant difference in GY and PFP_N between plant densities D2 and D3. Increasing the N application rate significantly increased the vascular bundle number (NVB) and area (AVB), however, excess N application (N3) did not significantly improve these parameters. N application significantly increased GY, whereas there was a significant decrease in PFP_N in response to an increase in N application rate. The two years results suggested that increasing the plant density (from 75 ×10⁴plants ha^-1to 336 ×10⁴plants ha^-1) in conjunction with the application of 290 kg N ha^-1N will maximize GY, and also increase PFP_N(39.7 kg kg^-1), compared with the application of 360 kg N ha^-1N. Therefore, an appropriate combination of increased planting density with reduced N application could regulate tiller number and favor the superior tiller group, to produce wheat populations with enhanced yield and NUE.