Implications of Inorganic Fertilization of Irrigated Corn on Soil Properties: Lessons Learned after 50 Years

Inorganic fertilizers are widely used for crop production, but their long‐term impacts on soil organic carbon (SOC) pools and soil physical attributes are not fully understood. We studied how half a century of N application at 0, 45, 90, 134, 179, and 224 kg ha −1 and P application at 0, 20, and 40 kg ha −1 (since 1992) affected SOC pools and soil structural and hydraulic parameters in irrigated continuous corn ( Zea mays L.) under conventional till on an Aridic Haplustoll in the central Great Plains. Application of 45, 90, 134, 179, and 224 kg N ha −1 increased the SOC pool by 4.6, 6.8, 7.6, 7.9, and 9.7 Mg ha −1 , respectively, relative to nonfertilized plots in the 0‐ to 45‐cm depth. Application of 20 kg P ha −1 increased the SOC pool by 2.9 Mg ha −1 in the 0‐ to 30‐cm depth. The highest N rate increased the SOC pool by 195 kg ha −1 yr −1 . The C gains may be, however, offset by the C hidden costs of N fertilization. Application of >45 kg N ha −1 reduced the proportion of soil macroaggregates (>0.25 mm) in the 7.5‐ to 30‐cm depth. Fertilization did not affect hydraulic properties, but application of ≥90 kg N ha −1 slightly increased aggregate water repellency. An increase in SOC concentration did not increase the mean weight diameter of wet aggregates ( r = 0.1; P > 0.10), but it slightly increased aggregate water repellency ( r = 0.5; P < 0.005). Overall, long‐term inorganic fertilization to irrigated corn can increase SOC pool, but it may reduce soil structural stability.