Nitrogen fertilization for wheat following soybean and interfering factors on spectral reflectance readings
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Nitrogen fertilization for wheat following soybean and interfering factors on spectral reflectance readings Claudio Kapp‑Junior1 · Alaine Margarete Guimarães2 · Eduardo Fávero Caires2 Received: 9 July 2020 / Accepted: 28 September 2020 © Springer Nature Switzerland AG 2020
Abstract A field experiment examined the wheat response following soybean due to urea-N fertilization at sowing (0, 20, 40, and 60 kg N ha−1) and top dressing (0, 30, 60, and 90 kg N ha−1). Normalized difference vegetation index (NDVI) measurements using a GreenSeeker active sensor were taken at different growth stages, at various sensor heights above the canopy, and at different times of day. Both the shoot dry matter yield and the grain yield were not affected by N fertilization at sowing and increased with increasing N rates at top dressing. A maximum economic yield was obtained at 55 kg N ha−1 in top dressing, causing a 33% increase in grain yield and an economic return of US$ 189.50 ha−1. Differences in NDVI were found before and after top-dressing N fertilization, indicating that GreenSeeker was efficient in monitoring wheat N nutrition. NDVI varied depending on the measurement distance, stabilizing from 0.30 to 1.20 m above the canopy. Because of the influence of incident radiation, higher NDVI values were obtained at the beginning and end of the day. The results suggest that for the wheat cultivar Quartzo following soybean under minimum soil disturbance, while there is no need to apply N at sowing, an important increase in grain yield can be obtained with top-dressing N fertilization. In addition, to improve the accuracy in developing N fertilizer recommendation models using GreenSeeker, a consistent protocol for spectral reflectance readings, mainly regarding the time of day, is required. Keywords Remote sensing · GreenSeeker · Timing of sensing · Measurement distance · NDVI
1 Introduction Wheat is grown in nearly every region of the world and represents a main source of food and income for millions of farmers. Wheat-based foods are critical for food security and nutritional security worldwide. The main world producers of wheat are the European Union, China, India, Russia, and the USA (USDA 2019). Although Brazilian wheat production is only around 6.0 million Mg, wheat is the main winter crop grown following soybean in southern Brazil. Wheat has a high nitrogen (N) requirement, and most of the N is required over a short period, during an exponential growth phase [25]. Usually, the soil supplies a certain
amount of N that depends on the soil organic matter mineralization, but this is not enough to provide all the needs of the plant and additional N fertilization is required to achieve highest yields [5]. An advantage under the soybean–wheat system is the contribution of the previous legume to reduce the need of N fertilizer application, since higher rates of decomposition and mineralization of N can be recycled and recovered by the crop in succession due mainly to the lower residue C/N ratio (about 20:1). Anyway, fertilizer N use is
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