Sustainable controlled-release urea placement depth reduces lodging risk and enhances spring maize productivity

Deep placement of controlled-release urea is an effective fertiliser management strategy for improving the maize productivity, but it is not clear whether and how controlled-release urea depth affects the stem and root lodging of spring maize. Two consecutive years of field experiments were conducted to elucidate stem and root lodging properties and their relationship between grain yield and lodging behaviours under various controlled-release urea placement depths. Results depicted that compared to broadcast nitrogen treatment (D0), deep controlled-release urea significantly decreased the stem lodging rate by 34.7-80.4%, which contributed to improving the mechanical characteristics of the internode by optimising the internode diameter and dry matter in the third basal internode as well as higher lignin content. In addition, due to a greater and deeper root system (root dry weight, root surface area, root length and root width) as well as larger angle, diameter, and tension of aerial root that significantly decreased root lodging rate (37.0-88.4%). Furthermore, deep placement of controlled-release urea significantly increased the 100-grain weight, grain number and harvested index by constructing a deeper and larger root system, which significantly improved maize grain yield by 14.2-38.5%, and the nitrogen use efficiency increased by 4.8-10.7%. The highest grain yield, nitrogen use efficiency and lowest lodging rate occurred in controlled-release urea placement depths of 15 cm. Hence, our study suggests that controlled-release urea placement depths of 15 cm were an efficient nitrogen fertiliser management strategy to improve crop productivity as well as lodging resistance in spring maize.