Eficiencia de la fertilizacion nitrogenada en sorgo con la tecnica isotopica 15N, en un vertisol con drenaje subsuperficial | Efficiency of nitrogen fertilization in sorghum using the 15N isotope technique in a vertisol with surface drainage

Soil nitrogen is the most limiting nutrient element for crop development. Knowing how it is absorbed by the plant when fertilizers are applied permits the assessment of its efficiency. In this study, the efficiency of nitrogen fertilization was evaluated in irrigated sorghum [Sorghum bicolor (L.) Moench], under three surface drainage spacing distances (EDS), (10, 20, and 40 m). At sowing (S) and floral differentiation (DF) 120 kg ha(-1) of nitrogen was applied. The 15N isotope technique was used in stem, leaves and grain sampled at floral differentiation (DF) and physiological maturity (MF). On average, biomass absorbed 83.1 and 88.7 kg ha(-1) of total N when it was applied at S and DF, respectively (171.8 kg ha(-1) for the entire cycle), justifying the fractioning of the total dose of N to favor increased use of fertilizer by the plant. Soil nitrogen absorbed by the crop surpassed absorbed fertilizer in plants at the three EDS and fertilized on both application dates. The yield of nitrogen from the fertilizer and the fertilizer nitrogen recovery efficiency (ERFN) in the biomass, and its components stem and leaves, were significantly higher when the nitrogen fertilizer was applied at sowing for the three EDS. ERFN in the grain was 88.8% when the fertilizer was applied during the stage of floral differentiation, relative to the total biomass for the period ADF-MF. It can be concluded from the assessment of ERFN in stem, leaves and grain in the three EDS and the two EA studied that nitrogen compounds are transferred from vegetative organs (leaves and stem) and stored in the grain after the stage of floral differentiation. Since this work was done during the drought season, the EDS did not induce marked differences in the soil water content and, therefore, they did not have a clear influence on the cultivation response to the fertilizer application.