Optimizing the fertilizer N rates at different irrigation levels for optimum yield of wheat and corn at reduced nitrate leaching losses

Optimizing fertilizer nitrogen rates and irrigation levels is crucial for maximizing crop yield while minimizing nitrate-nitrogen (NO3-N) leaching losses, all without incurring financial losses. A study conducted at the University of Agriculture Faisalabad, Pakistan, aimed to explore the effects of rational irrigation and nitrogen management on wheat and maize crop yields and NO3-N leaching losses over two years, focusing on wheat-fallow-corn seasons.

To collect leachates, suction lysimeters were installed, and soil water balance was calculated using the HYDRUS-1D model. Three irrigation and nitrogen levels (I1, I2, I3 for irrigation, and N1, N2, N3 for nitrogen) were tested for wheat and maize crops. These levels included 325/400/475 mm and 100/130/160 kg ha-1 for wheat, and 375/525/675 mm and 220/270/320 kg ha-1 for maize.

The findings revealed that increasing irrigation and nitrogen levels significantly enhanced the growth and yield of both crops during both seasons. The highest grain yields were observed under the I3N3 treatment for wheat (4.0 t ha-1) and maize (7.8 t ha-1). However, the I2N3 treatment, despite its lower nitrogen and irrigation levels, did not show a statistically significant difference in yield but significantly reduced NO3-N leaching losses by 28.6% (23.8 kg ha-1) and provided the highest financial benefits of 780$.

Irrigation water-use efficiency (WUEi) also rose by 12% in wheat and 20% in maize under the I2 treatment compared to the I3 level. Furthermore, the I2N3 treatment yielded the highest value cost ratio (1.64 and 2.04 for wheat and maize, respectively), outperforming other treatments. Based on the comprehensive analysis, the I2N3 treatment is recommended for sustainable yields and minimal environmental risks in the wheat-maize cropping system.

Additionally, the study noted that the rainy fallow period contributed 14.0-31.5% to the total NO3-N leaching losses. Further research is needed to minimize NO3-N leaching losses, particularly during the rainy fallow period, by early maize sowing and increasing fertilizer efficiency (such as coating) under flood irrigation systems to attain sustainable productivity and environmental security goals.