Field Modeling Study of Yield Response and Nitrate Leaching with Manure Application and Deficit Irrigation for Maize-Fallow-Wheat Rotation

A two-year field experiment was carried out in Pakistan to assess the impacts of applying 50 Mg ha-1 dairy manure annually, alongside urea, on wheat-fallow-maize rotation. The study focused on irrigation regimes at 100% and 75% of the reference evapotranspiration (ETc). The researchers employed suction lysimeters to collect nitrate-N leachates at a depth of 1.2 meters and utilized HYDRUS-1D to measure daily deep percolation losses.

The results demonstrated that the combination of manure and deficit irrigation yielded significant improvements in crop yield, water use efficiency, and soil health. Specifically, wheat and maize yields were reported at 4.36 and 7.80 Mg/ha, respectively, under manure with deficit irrigation, while water use efficiency reached 1.09 and 1.59 kg/ha/mm.

Notably, these benefits were not observed when full irrigation was used, either with manure or urea applications. In contrast, the absence of manure, regardless of irrigation regime, led to a noticeable decrease in yield.

In terms of environmental impact, the study found that manure with deficit irrigation resulted in an average annual nitrate-N leaching of 17.45 kg/ha, compared to 11.46 and 55.59% increases in leaching losses when urea or manure were applied with full irrigation, respectively. Importantly, neither irrigation regime showed any significant yield improvements when manure was not applied.

Overall, the findings suggest that deficit irrigation paired with manure application offers an optimal balance of yield optimization, reduced nitrate-N leaching risks, and enhanced soil physical properties in semi-arid cereal cropping systems.