Legacy effects of long-term nitrogen fertilizer application on the fate of nitrogen fertilizer inputs in continuous maize

• Published in: Agriculture, ecosystems & environment Vol. 265; pp. 544 - 555
• Main Authors: Poffenbarger, Hanna J., Sawyer, John E., Barker, Daniel W., Olk, Daniel C., Six, Johan, Castellano, Michael J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2018; Elsevier BV
• Subjects: Agronomy; carbon sequestration; Corn; Crop residues; Crop yield; Cropping systems; Crops; Fertilizer application; Fertilizers; Growing season; Iowa; Nitrogen; Nitrogen budget; nitrogen fertilizers; Nitrogen recovery efficiency; Nitrogen use efficiency; Organic farming; Organic matter; Organic soils; Particulate organic matter; Recovery; soil nutrient dynamics; soil organic carbon; Soil organic matter; Soils; Topsoil; Zea mays; United States > US; Iowa; Soil organic matter; Nitrogen use efficiency; Nitrogen recovery efficiency; Nitrogen budget
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2018.07.005

Mass per area and percentage of applied fertilizer N that was recovered in maize aboveground biomass, the soil profile (0–120 cm), and unrecovered at harvest in 2015. Each location received the empirically-determined agronomic optimum N rate in 2015. Fertilizer N recovery in each pool was averaged across historical N rate treatments. Error bars depict ± one SE. [Display omitted] •Soil N-supplying capacity increased with increasing long-term N fertilizer rate.•Historical N fertilizer rate impacted crop fertilizer N recovery efficiency.•Increasing historical N rate decreased fertilizer N retention in topsoil.•Nitrogen fertilizer budgets differed dramatically by location. Nitrogen fertilizer management can impact soil organic C (SOC) stocks in cereal-based cropping systems by regulating crop residue inputs and decomposition rates. However, the impact of long-term N fertilizer management, and associated changes in SOC quantity and quality, on the fate of N fertilizer inputs is uncertain. Using two 15-year N fertilizer rate experiments on continuous maize (Zea mays L.) in Iowa, which have generated gradients of SOC, we evaluated the legacy effects of N fertilizer inputs on the fate of added N. Across the historical N fertilizer rates, which ranged from 0 to 269 kg N ha−1 yr−1, we applied isotopically-labeled N fertilizer at the empirically-determined site-specific agronomic optimum rate (202 kg N ha−1 at the central location and 269 kg N ha−1 at the southern location) and measured fertilizer recovery in crop and soil pools, and, by difference, environmental losses. Crop fertilizer N recovery efficiency (NREcrop) at physiological maturity averaged 44% and 14% of applied N in central Iowa and southern Iowa, respectively (88 kg N ha−1 and 37 kg N ha−1, respectively). Despite these large differences in NREcrop, the response to historical N rate was remarkably similar across both locations: NREcrop was greatest at low and high historical N rates, and least at the intermediate rates. Decreasing NREcrop from low to intermediate historical N rates corresponded to a decline in early-season fertilizer N recovery in the relatively slow turnover topsoil mineral-associated organic matter pool (0–15 cm), while increasing NREcrop from intermediate to high historical N rates corresponded to an increase in early-season fertilizer N recovery in the relatively fast turnover topsoil particulate organic matter pool and an increase in crop yield potential. Despite the variation in NREcrop along the historical N rate gradient, we did not detect an effect of historical N rate on environmental losses during the growing season, which averaged 34% and 69% of fertilizer N inputs at the central and southern locations, respectively (69 kg N ha−1 and 185 kg N ha−1, respectively). Our results suggest that, while beneficial for SOC storage over the long term, fertilizing at the agronomic optimum N rate can lead to significant environmental N losses.