Management of nitrogen fertilization to balance reducing lodging risk and increasing yield and protein content in spring wheat

Crop lodging (stem and root lodging) is one of the main constraints limiting grain yield and quality in spring wheat production, especially under high–yielding conditions. Few studies have been conducted to clarify the trade–off between grain yield and lodging resistance, and assess whether it is possible to manage lodging risk without a yield reduction penalty. Developing appropriate nitrogen (N) fertilizer management strategies for driving grain yield/quality while reducing (or at least not increasing) the risk of lodging is needed to achieve this. The risks of stem and root lodging were quantified by “safety factor” (SF) indicator, which represents the number of times a support organ can bear the self–weight moment of the organ that it is supporting. Two varieties with contrasting stature (tall vs. semi–dwarf), were tested under different timing and rates of N application strategies. The advantage of split–N (preplant plus top–dress application at the jointing stage) over equivalent preplant–only N application was not evidenced on yield, but grain protein (%) was improved by up to 7.5% without a yield penalty. The risk of lodging was increased with increasing N rates from zero to the highest N treatment, as indicated by decreasing stem safety factor SFs (–23.7%) and root safety factor SFr (–32.2%) across both years, and increasing visual lodging score (by 7–fold) in 2017. The split–N treatment N50 + 50 (50 kg N ha–1 at preplant plus 50 kg N ha–1 at jointing stage) showed a promising lodging resistance with SFs, SFr and visual lodging scores similar to the zero N treatment. Taken together, the moderate split–N application (N50 + 50) is recommended due to the relative high grain protein (%) and strong lodging resistance while sustaining a promising yield. Spring wheat was more susceptible to root lodging than to stem lodging in the specific conditions of these experiments. Additionally, breeding for and cultivation with cultivars with improved stem strength is likely to be required to counter the escalating lodging risk arising from continued yield increases.