Optimizing nitrogen fertilizer input using fallow season precipitation for dryland winter wheat

Area of Science:

• Agricultural Science
• Agronomy
• Soil Science

Background:

• Precipitation variability is a primary driver of yield fluctuations in rainfed agriculture on the Loess Plateau.
• Overfertilization with nitrogen (N) presents significant economic and environmental challenges.
• Optimizing N management in relation to fallow season precipitation is critical for improving crop water use efficiency (WUE) and yield in dryland farming systems.

Purpose of the Study:

• To establish reference ranges for wheat cultivation year types based on historical precipitation data.
• To determine optimal nitrogen (N) application rates for maximizing wheat yield and WUE under varying precipitation conditions.
• To investigate the relationship between precipitation frequency (PF) and wheat yield in a rainfed system.

Main Methods:

• Analysis of 37 years of fallow season precipitation data to define dry, normal, and wet years.
• An 8-year field experiment employing a randomized block design with seven N rates (0–240 kg N ha⁻¹).
• Non-linear regression analysis to assess the correlation between yield, precipitation frequency, and N input.

Main Results:

• Defined precipitation ranges: dry (<220.7 mm), normal (220.7–346.2 mm), and wet (>346.2 mm).
• Optimal N rates varied by year type: 150 kg ha⁻¹ (dry), 150–180 kg ha⁻¹ (normal), and 210 kg ha⁻¹ (wet).
• Yield and WUE were maximized by increasing spike number per hectare through optimized N input; a 1% increase in PF to total precipitation ratio yielded 46 kg ha⁻¹ more.

Conclusions:

• Adjusting nitrogen fertilizer application based on seasonal rainfall variations is crucial for enhancing wheat yield and WUE in rainfed farming systems.
• The study provides a framework for optimizing N management in dryland agriculture, mitigating risks associated with rainfall variability.
• Understanding the impact of "drought at sowing" versus "drought in growing season" is vital for effective N management strategies.