Effect of nitrogen topdressing on planting density response of grain yield in maize with different planting pattern cultivation

We investigated the maize grain yield in response to nitrogen topdressing at different planting densities and planting patterns (twin row, TR; narrow row, NR; and conventional row, CR) over 3 years using early-maturing cultivars. The P8025 grain yield was higher with a nitrogen topdressing of 6 g/m(2) (N6) than without a nitrogen topdressing (N0) at all planting densities in 2017, 2018, and 2019. The difference between the nitrogen topdressing treatments was largest at a planting density close to 10 plants per square meter, which resulted in the highest grain yield in the N0 plot. The rank order for the grain yields among planting patterns was TR >= NR > CR in the three analyzed years. Changes in grain yield associated with planting densities followed significant negative quadratic regression curves for all planting patterns. In both the N0 and N6 plots, the grain yield response to planting density was more stable for TR cultivation than for CR and NR cultivation. The rank order for the nitrogen use efficiency (NUE) among planting patterns was TR >= NR >= CR. The differences in the NUE among planting patterns were higher at higher planting densities. The high NUE observed for TR and NR cultivation was due to the high topdressed nitrogen absorption rate (Nab) at a planting density less than 8.9 plants per square meter as well as the efficiency of the grain yield increase resulting from absorbed nitrogen (Ngy) at a planting density greater than 10.3 plants per square meter. The higher NUE for TR cultivation than for NR cultivation at 12.1 plants per square meter was because of a difference in Ngy and was unrelated to Nab. These results suggest that the improvement of planting pattern (TR, NR) can enhance the effect of topdressed nitrogen on grain yield in maize due to the increase of Nab or Ngy according to the planting density.