Differences in grain yield responses to planting density in twin and narrow row cultivation between early and late maize cultivars

We investigated how two planting patterns, twin row (TR) and narrow row (NR), affected maize grain yield compared with conventional row (CR) cultivation at five different planting densities, ranging from 7 to 12 plants/m 2 , over 2 years using early and late cultivars. For all the planting patterns, the relationship between grain yield and planting density could be fit using the quadratic curve Y  =  a ( X − b ) 2  +  c at the <1% level of significance, where a represents grain yield response to planting density, and c represents the maximum yield. Regardless of the cultivar’s maturation period, the magnitude of a was smaller for TR than for NR and CR. Although the late cultivar had a higher c value than the early cultivar, the a value and annual difference were larger. For the early and late cultivars, TR at 10.8 and 9.9 plants/m 2 , respectively, easily achieved stable high grain yields. The large magnitude of the grain yield response to planting density for the late cultivar was caused by the large decrease in the number of grains per ear and the harvest index at an above optimum planting density. This large decrease and instability in yield‐related traits resulted from a high maximum leaf area index, the frequent mutual shading of leaf blades and the large differences between the years.