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

Citation

Wu, W., Ma, B.L., Fan, J.J., Sun, M., Yi, Y., Guo, W.S., Voldeng, H.D. (2019). Management of nitrogen fertilization to balance reducing lodging risk and increasing yield and protein content in spring wheat. Field Crops Research, [online] 241 http://dx.doi.org/10.1016/j.fcr.2019.107584

Plain language summary

In wheat, continuing improvement in grain yield and quality to meet the swelling market demand of increasing populations for human consumption remains a top priority. Wheat yield and grain protein are dependent on genetic background, environmental condition and crop management practices, such as nitrogen (N) fertilizer management, irrigation regime, sowing date, planting density and tillage practices. Among these strategies, the method of applying N fertilizer is generally the most effective input for increasing yield and grain protein (%) in wheat production. Excessive N applications have considerably decreased N use efficiency and led to severe environmental contamination because of substantial N loss, such as N leaching, volatilization and denitrification. Therefore, efficient N fertilizer management is important for developing a sustainable strategy for improving grain yield and quality while generating less environmental harm. Under high–yielding conditions, however, crop lodging risk is often increased to reduce grain yield and quality conversely. The motivation to promote grain yield makes crop lodging a common problem, which is perhaps underestimated, and constantly increasing as yield increases, under favorable weather conditions, such as in present humid environment of eastern Canada. Lodging significantly suppresses photosynthetic ability, carbohydrate transportation, and nutrient and water movement within the plant. Crop lodging is generally categorized as stem lodging and root lodging. Root lodging is caused by the failure of the root–soil anchorage system or the displacement of the roots within the soil that is related to the inferior coronal root bending strength, small diameter of the root–soil cone and poor soil shear strength; whereas stem lodging is mostly related to the mechanical characteristics of basal internodes. Additionally, the stem and root lodging in response to N fertilizer management may be dissimilar and the underlying mechanisms should be differentiated.

The objectives of this study were to (1) clarify the trade–off between grain yield and lodging resistance, and assess whether it is possible to manage lodging risk without a yield penalty, through optimizing N fertilizer strategy; (2) distinguish whether the spring wheat has more risk of stem or root lodging; and (3) determine the relationships between canopy reflectance (normalized difference vegetation index - NDVI reading) and lodging susceptibility. A field experiment was conducted for two years to address the objectives.

We found that a moderate N rate of 100 kg ha–1 could fully express yield potential, and further increases in N rate beyond 150 kg ha–1 did not obtain any yield gains and may even reduce the crop profitability. In this study, we demonstrated a lack of consistent benefit of split–N over preplant only N application on yield, but positive effects on grain protein (%) and lodging resistance. Taken together, the split–N treatment (50 kg ha-1 at preplant plus 50 kg ha-1 at jointing stage) can be recommended for spring wheat production in eastern Canada, due to its relative high grain protein (%) and strong lodging resistance but without a decreasing yield. Under the specific conditions tested, root lodging was more prevalent than stem lodging, as evidenced by the smaller safety factor (SF) for roots compared with SF for stems, and the observed deformation of root–soil cores, but without any buckling or bending point of the stem when lodging actually occurred. Although stem lodging was not as prevalent as root lodging, improving both types of lodging resistance is likely to be required to obtain further yield improvements without increasing the frequency of lodging. The results of a positive correlation between NDVI mapping data and the lodging susceptibility indicated the applicability of using the NDVI indicator to guide N fertilizer strategies to mitigate the lodging risk, which deserves further study.

Abstract

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.

Publication date

2019-09-01

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