Effect of variable rate irrigation and nitrogen fertilizer rates on crop productivity and water quality

Under deficit irrigation, nitrogen (N) fertilizer strategies must be carefully adjusted to sustain profitable crop production while minimizing environmental impacts. In Minnesota, however, the combined influence of irrigation and nitrogen (IxN) management on corn yield, evapotranspiration, and nitrate leaching has not been extensively quantified under real-world conditions. Current N recommendations in the state are largely based on either fully irrigated (100% I) or rainfed systems, leaving a gap in guidance for producers adopting deficit irrigation strategies, which are increasingly promoted due to water resource limitations and concerns over groundwater nitrate contamination. This 5-year study was designed to address a key question: Can reductions in irrigation be paired with optimized nitrogen rates to maintain yield while minimizing nitrate leaching? Furthermore, what are the best IxN combinations for balancing economic returns, environmental protection, and system resilience under variable Minnesota weather? Through replicated field trials at two sites (Becker and Westport), this research established foundational, field-tested relationships between yield, ET, water input, nitrogen uptake, and nitrate leaching across a matrix of irrigation and nitrogen rates. Key findings show that full yield potential can be achieved using moderate irrigation (I2, 75% I) combined with nitrogen rates of 210–250 lb/ac (N4–N5). These combinations consistently produced high yields, high water use efficiency, and minimal nitrate loss, demonstrating that more input does not always mean more output.