Leaf Scorching following Foliar Fertilization of Wheat with Urea or Urea–Ammonium Nitrate Is Caused by Ammonium Toxicity

Abstract

Foliar fertilization is a potential tool to increase the use-efficiency of nitrogen (N) fertilizers. However, whilst leaf scorching has frequently been reported, the underlying physiological processes are not clear. In the present work, we investigate the intensity of leaf scorching as affected by the balance between ammonium assimilation and accumulation. Leaves were sprayed with urea–ammonium nitrate (UAN) solution without surfactant or applied liquid droplets of urea in different N concentrations with surfactant. UAN solutions without surfactant containing >10% N caused leaf scorching already after 24 h and the severity increased with the N concentration. The same pattern was observed 3 days after the application of urea solutions containing >4% N together with surfactant. The scorching was accompanied by a massive increase in foliar and apoplastic ammonium (NH4+) concentration. Moreover, the activity of glutamine synthetase (GS), most pronouncedly that of the chloroplastic isoform (GS2), decreased a few hours after the application of high N-concentrations. Along with this, the concentration of glutamate—the substrate for GS—decreased. We conclude that leaf scorching is promoted by NH4+ accumulation due to a limitation in N assimilation capacity.

Comparative Efficacy of Foliar Plus Soil Application of Urea versus Conventional Application Methods for Enhanced Growth, Yield, Agronomic Efficiency, and Economic Benefits in Rice

“…The highest number of effective tillers (18.67) was recorded in the T 8 treatment, which was statistically similar to the T 7 , T 6, and T 10 treatments, while the lowest (12.67) was in the T 1 treatment. The results of the present experiment agreed well with the findings of other researchers who concluded that foliar application of urea significantly increased the number of effective tillers hill –1 of BRRI dhan29. − Foliar spraying of 3% urea solution produced a higher number of effective tillers hill –1 than 1% urea spraying . Soil (75%) and foliar (10%) application of urea significantly increased the effective tillers of Binahsail and BRRI dhan46 varieties during the T. aman season .…”

“… 11 − 17 Foliar spraying of 3% urea solution produced a higher number of effective tillers hill –1 than 1% urea spraying. 31 Soil (75%) and foliar (10%) application of urea significantly increased the effective tillers of Binahsail and BRRI dhan46 varieties during the T. aman season. 12 Many studies showed that the soil and foliar application of N increased the number of effective tillers hill –1 in many crops.…”

Optimizing foliar N‐fertilization in sugarcane depends on plant genotype and nitrogen concentration

“…However, it is essential to consider both, environmental conditions (Thorburn et al 2017; Dias and Sentelhas 2018; Castro et al 2019) and the N requirement of the plant (de Oliveira et al 2013; Leite et al 2016; Mariano et al 2016) to promote great NUE and NRP, minimizing nitrogen losses, and supporting sustainable agricultural practices (Zhang et al 2015; Bowles et al 2018). Adjusting the timing of N‐fertilizer application (Lofton and Tubaña 2015; de Castro et al 2022) and employing appropriate application methods (Borges et al 2019) have been found to reduce greenhouse gas (GHG) emissions and improve NUE in sugarcane. However, these actions alone are insufficient as a significant proportion of nitrogen becomes immobilized in the soil (Otto et al 2016; Quassi de Castro et al 2021; Sanches and Otto 2022).…”

“…High concentrations of ammonium and urea, which are components of N-urea fertilizers, have been shown to be toxic to plants in prior studies (Krogmeier et al 1989;Tan et al 1999 in 15 NL of all sugarcane varieties studied (Figure 6). This might leads to a probable increase in the ammonium content, which is the primary product of urea hydrolysis (Witte 2011;Castro et al 2022). The assimilation of ammonium into glutamine and glutamate contributes to the accumulation of protons, leading to abiotic stress in plants (Britto and Kronzucker 2005;Masclaux-Daubresse et al 2010;Hachiya et al 2021).…”

“…Nonetheless, FNf can present negative effects, for example, leaf scorching, if the nutrient rate and application timing are not adequate (Johnson et al 2001; Moore and Botha 2014). Leaf scorching is mainly promoted by ammonium accumulation (Krogmeier et al 1989; Hachiya et al 2021; Castro et al 2022), at rates higher than 20 kg N ha −1 (Sangplung and Rosário 1978).…”