Analysis of vegetation indices to determine nitrogen application and yield prediction in maize (Zea mays L.) from a standard UAV service

The growing use of commercial unmanned aerial vehicles (UAV) and the need to adjust N fertilization rates in maize (Zea mays L.) currently constitute a key research issue. In this study, different multispectral vegetation indices (green-band and red-band based indices), SPAD and crop height (derived from a multispectral compact camera mounted on a UAV) were analysed to predict grain yield and determine whether an additional sidedress application of N fertilizer was required just before flowering. Seven different inorganic N rates (0, 100, 150, 200, 250, 300, 400 kg·N·ha−1), two different pig slurry manure rates (Ps) (150 or 250 kg·N·ha−1) and four different inorganic-organic N combinations (N100Ps150, N100Ps250, N200Ps150, N200Ps250) were applied to maize experimental plots. The spectral index that best explained final grain yield for the N treatments was the Wide Dynamic Range Vegetation Index (WDRVI). It identified a key threshold above/below 250–300 kg·N·ha−1. WDRVI, NDVI and crop height showed no significant response to extra N application at the economic optimum rate of fertilization (239.8 kg·N·ha−1), for which a grain yield of 16.12 Mg·ha−1 was obtained. This demonstrates their potential as yield predictors at V12 stage. Finally, a ranking of different vegetation indices and crop height is proposed to overcome the uncertainty associated with basing decisions on a single index.This work was funded by the Spanish Ministry of Science and Innovation (Project AGL2012-35122). The authors also would like to thank the IRTA Research Station (Gimenells, Lleida) for allowing the research to take place, the GIS & Remote Sensing Laboratory of the University of Lleida for the facilities to carry out the image processing and analysis, and the University of Lleida for the PhD scholarship of Ángel Maresma

Erratum: Maresma, A., et al. Analysis of Vegetation Indices to Determine Nitrogen Application and Yield Prediction in Maize (Zea mays L.) from a Standard UAV Service. Remote Sens. 2017, 9, 648

After publication of the research paper [1], the authors noticed an error and wish to make the following correction.[...

Improvement of the nitrogen fertilization in irrigated Mediterranean environments

Un dels principals mètodes per incrementar els rendiments del cultius és l'aplicació de fertilitzants, principalment el nitrogen (N). Aplicacions insuficients de N poden provocar importants pèrdues econòmiques per als agricultors, mentre que aplicacions excessives incrementen el risc de contaminació ambiental. La present tesi doctoral pretén contribuir al desenvolupament de sistemes agrícoles més sostenibles mitjançant la millora de l'eficiència del N. Protocols sobre el mostreig de sòls, imatges aèries multiespectrals i estratègies de doble cultiu han estat analitzades per millorar les pràctiques de fertilització nitrogenada. Densitats òptimes de mostreig de sòl de 3.75 i 12.5 mostres/ha es van determinar per a la matèria orgànica (MO) i pel contingut de nitrats, respectivament. En una altre capìtol de la tesis, els índexs de vegetació basats en el verd van ser més precisos que els basats en el vermell per predir el rendiment de gra del blat de moro i la dosi òptima de fertilització en V12. El sistema de doble cultiu anual (ordi-blat de moro) va tenir produccions de 20 Mg de gra/ha i 35 Mg de biomassa/ha, amb aplicacions anuals de 230-240 kg de N/ha dividides entre els dos cultius, mostrant l'alt potencial de rendiment i la seva estabilitat comparativament amb estratègies de monocultiu.Uno de los principales método para incrementar los rendimientos es la aplicación de fertilizantes, principalmente el nitrógeno (N). Aplicaciones insuficientes de N pueden provocar graves pérdidas económicas para los agricultores, mientras que aplicaciones excesivas incrementan el riesgo de contaminación ambiental. La presente tesis doctoral pretende contribuir al desarrollo de sistemas agricolas más sostenibles mediante la mejora de la eficiencia del N. Protocolos de muestreo de suelos, imágenes aéreas multiespectrales y estratégias de doble cultivo anuales han sido analizadas para mejorar las prácticas de fertilización nitrogenada. Densidades óptimas de muestreo de 3.75 y 12.5 muestras/ha se determinaron para materia orgánica (OM) y nitratos, respectivamente. En otro capítulo de la tesis, los indices de vegetación basados en el verde fueron más precisos que los basados en el rojo para predecir el rendimiento de grano del maíz y la dosis óptima de fertilización en V12. El sistema de doble cultivo anual (cebada-maíz) obtuvo producciones de 20 Mg de grano/ha y 35 Mg de biomasa/ha, con aplicaciones anuales de 230-240 kg N/ha divididas entre los dos cultivos, mostrando el alto potencial de rendimiento y su estabilidad cuando se compara con estrategias de monocultivo.One of the main methods for increasing yields is the application of mineral fertilizers, mainly nitrogen (N). Insufficient application of N can have serious economic consequences for the farmer, whereas excessive fertilization increases the risk of environmental pollution. Traditionally, N fertilization of field crops, such as maize, has been adjusted by yield-based N recommendations methods.The present Ph.D. Thesis aims to contribute to the development of more sustainable agricultural systems by improving nitrogen efficiency. Soil sampling protocols, multispectral aerial images and double-annual cropping strategies and methods were analysed to improve the N fertilization practices. Optimum soil sampling densities of 3.75 and 12.5 samples/ha were determined for organic matter (OM) and nitrates, respectively. In other chapter of the Thesis, Green-based vegetation indices (VIs) were more accurate than red-based ones in predicting grain yield and in determining the optimum N rate for maize at V12 stage. Doble-annual cropping systems (barley-maize) yield up to 20 Mg of grain/ha and 35 Mg of biomass/ha, with annual N rates of 230-240 kg N/ha split between both crops, showing high yielding potential and yield stability when compared with mono-cropping strategies