Agronomy Journal • Volume 109, Issue 5 • 2017 1 M aize is the second most important crop globally in terms of cultivation area and revenue, and it is therefore important to understand in detail how this crop responds to production inputs (Desjardins, 2014). Nitrogen is the most intensively studied fertilizer component because it is essential for plant growth and has a major impact on yield (Cardwell, 1982). Optimal N inputs translate directly into profts for maize farmers (Pikul et al., 2005) whereas insuf- fcient N leads to poor yields, poor human nutrition, and soil degradation (Sánchez and Swaminathan, 2005). Nitrogen fertilization represents ~20% of overall maize pro- duction costs in high-yielding areas under sprinkler irrigation (Lloveras and Cabases, 2014). However, excess N applications lead to environmental contamination due to N volatilization, runof, and leaching. Nitrates are one of the most common forms of groundwater contamination in Europe. To reduce nitrate pollution, the Nitrates Directive 91/676/CEE limits the amount of N that can be applied to agricultural land in European vulnerable zones (European Union, 1991). Maize crops show variable responses to the application of N fertilizer due to di ferences in genotype, soil characteristics, and climate in diferent regions and seasons (Hanway, 1962; Karlen et al., 1987; Cerrato and Blackmer, 1990; Berenguer et al., 2009). Most crops incorporate less than 50% of N inputs (Fageria and Baligar, 2005) so the improvement of N utiliza- tion is an important agronomic, economic, and environmental goal (Zhang et al., 2015). Tis is facilitated by the assessment of long-term responses to N in di ferent maize agricultural systems, particularly by investigating N availability and NUE to optimize the GY. Te NUE is usually defned as the ratio of N in the harvested product to the amount of N supplied as fertilizer (Quemada and Gabriel, 2016) or the ratio of GY to the amount of available soil N (Moll et al., 1982; López-Bellido et al., 2005). Te NUE afects many of the recently proposed/ defned Sustainable Development Goals (SDGs) for the post- 2015 era, recently accepted by 193 countries of the United Nations General Assembly (SDSN, 2015). Improving the NUE of crops is one of the most efective means of increasing produc- tivity and proftability while reducing environmental damage (Cassman et al., 2003; Davidson et al., 2015). Long-Term Effects of Mineral Nitrogen Fertilizer on Irrigated Maize and Soil Properties E. Martínez,* A. Maresma, A. Biau, S. Cela, P. Berenguer, F. Santiveri, A. Michelena, and J. Lloveras Published in Agron. J. 109:1–11 (2017) doi:10.2134/agronj2017.01.0020 Copyright © 2017 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved AbstrAct Nitrogen is a key determinant of growth and grain yield (GY) in maize (Zea mays L.) and is therefore economically and environ- mentally important. We investigated the performance of maize crops in a 12-yr experiment (2002–2007, 2010–2015) under sprinkler irrigation in a petrocalcic calcixerept soil in northeast- ern Spain, with controlled mineral N application rates (0, 100, 150, 200, 250, 300, and 400 kg N ha –1 yr –1 ). Te application rate afected maize GY, biomass, N uptake, SPAD units, soil N levels, N efciencies, and soil organic carbon (SOC). Aver- age maximum GY’s (~15 Mg ha –1 ) required 203 kg N ha –1 of available N (defned as initial soil NO 3 – plus N fertilizer) in the 0- to 30-cm horizon, confrming the importance of the soil N content. Nitrate levels in the 0- to 30-cm horizon for maximum yields achieved a R 2 value in the plateau ftting model similar to the 0- to 60- and 0- to 90-cm horizons. Te GY’s increased at a rate of 192 kg ha –1 yr –1 , suggesting a combination of genetic improvement in the hybrids and also an improvement in agro- nomic management. Te 200 kg N ha –1 fertilizer treatment achieved almost the highest GY’s (~14 Mg ha –1 ) with simulta- neous high nitrogen use efciency (NUE) (0.83 kg kg –1 ). Min- eral N fertilization also increased the stock of SOC in the 0- to 30-cm horizon. Univ. de Lleida, Agrotecnio, Av. Rovira Roure, 191, 25198, Lleida, Spain. Received 12 Jan. 2017. Accepted 14 Apr. 2017. *Corresponding author (elias.martinez@pvcf.udl.cat). Abbreviations: ANE, agronomic nitrogen efciency; ANR, apparent nitrogen recovery fraction; CNC, critical nitrogen concentration; GY, grain yield; NUE, nitrogen use efciency; PPNT, pre-planting nitrogen content; PSNT, pre-side dressing nitrogen content; SOC, soil organic carbon. core Ideas • Grain yield, biomass, N uptake, SPAD units, soil N levels and N efciciencies were afected by the N application rate. • Maximum grain yields required 203 kg N ha –1 of available N in the 0- to 30-cm layer soil. • Sampling to a depth of 0 to 30 cm provided similar correlations than sampling to 0 to 60 and 0 to 90 cm. • Mineral N fertilization increased soil organic C stock. Agronomy, soIls & EnvIronmEntAl QuAlIty Published online June 30, 2017