Evaluation of acidifying nitrogen fertilizers in avocado trees with iron deficiency symptoms

Abstract

The control of iron chlorosis by synthetic Fe chelates is costly, and their application can have adverse environmental impacts. We investigated the effectiveness of alternative strategies to prevent Fe chlorosis in avocado based on different acidifying nitrogen fertilizers. The experiment was conducted on a commercial orchard of avocado cv. Hass cultivated in a calcareous soil. The application of (NH 4 ) 2 SO 4 was highly effective at reducing the soil pH and, when applied with a nitrification inhibitor, at increasing the leaf chlorophyll concentration in trees. Fertilization with urea was also effective at increasing leaf chlorophyll, but only when applied without a nitrification inhibitor. However, the acidifying effect of urea on the soil was significantly lower than (NH 4 ) 2 SO 4 . The different N sources also modified the concentration of N-NO 3 -, N-NH 4 + and total N within the leaves, but did not influence the length of the shoots or the leaf gaseous exchange. These results suggest that the fertilization strategy based on (NH 4 ) 2 SO 4 + DMPP or urea can be an effective and sustainable alternative to counteract Fe chlorosis symptoms in avocado trees. Our results provide evidence of the effectiveness of agronomic strategies, alternative to synthetic Fe chelates, for preventing Fe deficiency in avocado.

Evaluation of FE-heme Applications or Intercropping for Preventing Iron Deficiency in Blueberry

“…Strategy I plants, corresponding to dicots like blueberry and non-graminaceous monocots, uptake Fe from the soil as Fe 2+ . In alkaline and sub-alkaline soils, Fe 2+ is commonly oxidized to the less soluble Fe 3+ (Golshahi et al 2018;Granja and Covarrubias 2018). In this case, Fe deficiencytolerant strategy I species are able to extrude protons into the rhizosphere by root plasma-membrane ATPase enzyme activity, lowering the pH of the soil solution and increasing the solubility of Fe 3+ , and/or increasing the root ferric-chelate reductase (FCR) enzyme activity to reduce Fe 3+ to Fe 2+ (Granja and Covarrubias 2018).…”

“…In alkaline and sub-alkaline soils, Fe 2+ is commonly oxidized to the less soluble Fe 3+ (Golshahi et al 2018;Granja and Covarrubias 2018). In this case, Fe deficiencytolerant strategy I species are able to extrude protons into the rhizosphere by root plasma-membrane ATPase enzyme activity, lowering the pH of the soil solution and increasing the solubility of Fe 3+ , and/or increasing the root ferric-chelate reductase (FCR) enzyme activity to reduce Fe 3+ to Fe 2+ (Granja and Covarrubias 2018). In addition, Fe deficiencytolerant genotypes react to Fe scarcity by increasing the concentration of some organic acids (mainly citric and malic acid) in root cell and xylem sap (Covarrubias and Rombolà 2015;Covarrubias et al 2016) and the root exudation of phenolic compounds in Arabidopsis thaliana (Fourcroy et al 2015).…”

“…On the other hand, the prevention/cure of Fe chlorosis with Fe chelates is a widespread agronomical practice in orchards (Bastani et al 2018). Nevertheless, such an approach involves high costs and environmental and health risks (Granja and Covarrubias 2018). Iron chelates are expensive (representing 60% of total fertilization costs in orchards located in calcareous soils) and, therefore, their use is economically justified only for extremely high-value crops (Granja and Covarrubias 2018).…”

“…Nevertheless, such an approach involves high costs and environmental and health risks (Granja and Covarrubias 2018). Iron chelates are expensive (representing 60% of total fertilization costs in orchards located in calcareous soils) and, therefore, their use is economically justified only for extremely high-value crops (Granja and Covarrubias 2018). In addition, Fe chelates require repeated applications and, due to their high stability and solubility, increase the risk of metal leaching and chelating agents in the deep soil layers and in the water table (Granja and Covarrubias 2018).…”

Nano iron (Fe) complex is an effective source of Fe for tobacco plants grown under low Fe supply

“…In aerobic soil, the majority of Fe is converted to the oxidised ferric form, which is extremely immobile in soil, leading to Fe deficiency in plants. In addition, soil pH in the range of 7.4-8.5 causes low solubility and slow dissolution kinetics of Fe-bearing minerals (Granja and Covarrubias, 2018). Also elevated bicarbonate concentrations, typical of calcareous soils, reduce the Fe acquisition by plants.…”