Nitrogen absorption-redistribution and physiological consequences of urea applied on the wheat leaves

Abstract

Nitrogen is one of the nutrients that most limits plant biomass production, presenting an important function in the photosynthesis process. In order to increase the agricultural crops yield, high N-fertilizer rates are used. The N-fertilizer use efficiency (NUE) by plants is low, in the wheat and sugarcane crops is ~33 and 25%, respectively. The low NUE is explained by the N immobilization in the soil. The N-fertilizer immobilized in the soil will be mineralized, and can be lost by leaching, reaching the watercourses and the groundwater, and by denitrification, emitting nitrous oxide. To solve these environmental problems, public policies are being established to ration the N-fertilizer use. An alternative to this current scenario is the leaf nitrogen fertilization use that provides a decrease in the N-fertilizer rates and increases the NUE by the plant, according to the preliminary results of the FAPESP 2017/25489-3 project. To better understand the higher NUE, it is important to evaluate the physiological plant responses, as well as to evaluate the substrates use that can increase the N assimilation (e.g. sucrose and glutamate) applied to the leaves and that act in the absorption process (e.g. silicon) and urea crystallization (e.g. Propylene glycol). Physiological evaluations include the leaf gas exchange parameters quantification, ammonium and urea accumulation, amino acids synthesis, glutamine synthetase and urease activity, leaf scorching and chlorophyll content. The silicon distribution in the leaf will also be evaluated. These assessments will be carried out under the supervision of Dr Jan K. Schjoerring, University of Copenhagen. The results will help to develop urea solutions for foliar fertilization allowing to reduce the N-fertilizer rates in wheat and sugarcane crops, reducing N losses to the environmental. (AU)