Uptake and allocation of nitrogen applied at low rates to soybean leaves

• Published in: Plant and soil 2015-08, Vol.393 (1-2), p.83-94
• Main Authors: Pierozan, Clovis, Jr, Favarin, José Laércio, de Almeida, Rodrigo Estevam Munhoz, Maciel de Oliveira, Silas, Lago, Bruno Cocco, Trivelin, Paulo Cesar Ocheuze
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; climate; Climatic conditions; Crop science; Crop yield; crops; developmental stages; Ecology; Fertilizer application; Fertilizers; foliar application; Glycine max; grain yield; grains; hulls; Leaves; Life Sciences; Nitrogen; Nitrogen content; nitrogen fertilizers; nitrogen fixation; nutrient use efficiency; Nutritional aspects; Plant Physiology; Plant Sciences; Plant-soil relationships; rain; Regular Article; seed yield; Shoots; soil; Soil fertility; Soil Science & Conservation; Soils; Soybean; Soybeans; stable isotopes; stems; Urea; urea nitrogen
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-015-2468-7

BACKGROUND AND AIMS: Foliar nitrogen (N) fertilization of soybean crops is a practice that is being adopted in Brazil because soybean crops require N during the reproductive stages and certain soils have low N availability and reduced biological N fixation (BNF). Thus, low rates of leaf N are being used without scientific evidence for supporting the practice. The aim of this study was to analyze the uptake efficiency and allocation of N provided by foliar applications of low rates of urea-N during the soybean reproductive stage. METHODS: The study was conducted in Taquarituba, Sao Paulo State (SP), Brazil during the 2012/13 and 2013/14 crop seasons. Rates of 0, 650, 1300 and 1950 g N ha⁻¹ applied at the R1 or R3 growth stage were analyzed. Grain yield, N extraction by the grains, shoots (including leaves + stems + pod husks), total plants (grains + shoots), N derived from fertilizer (NDFF), ¹⁵N accumulation in grains or shoots, and fertilizer N-use efficiency by plant (NUE) were measured using ¹⁵N. RESULTS: Foliar application of 1950 g ha⁻¹ of N increased the N content in the shoots by up to 22 kg ha⁻¹. Regardless of the year, the application during R3 yielded the highest NDFF values in the grains that were, on average, 20 % higher than in R1. However, the highest mean values of NDFF and NUE were obtained from the R3 or R1 applications when there was less rainfall. Despite the high NUE (64 %), foliar applications of low rates of N on soybean crops did not increase the seed yield. CONCLUSIONS: Most of the fertilizer N was allocated to the grains, especially when applied at the R3 growth stage. The NUE of the soybean crop ranged from 51 to 72 %, and it was dependent on the phenological stage of the crop and climate conditions during crop growth in addition to the timing of fertilizer application. Foliar application of low rates of N on soybean crops did not increase seed yield.