Abstract
Currently, fertilization with synthetic chelates is the most effective agricultural practice to prevent iron (Fe) deficiencies in crops, especially in calcareous soils. Because these compounds are not biodegradable, they are persistent in the environment, and so, there is the risk of metal leaching from the soils. Thus, new, more environment-friendly efficient solutions are needed to solve iron-deficiency-induced chlorosis (IDIC) in crops grown in calcareous soils. Therefore, the central aim of this work was to prepare new freeze-dried Fe products, using a biotechnological-based process, from two siderophores bacterial (Azotobacter vinelandii and Bacillus subtilis) cultures (which previously evidenced high Fe complexation ability at pH 9) and test their capacity for amending IDIC of soybean grown in calcareous soils. Results have shown that A. vinelandii iron fertilizer was more stable and interacted less with calcareous soils and its components than B. subtilis one. This behavior was noticeable in pot experiments where chlorotic soybean plants were treated with both fertilizer products. Plants treated with A. vinelandii fertilizer responded more significantly than those treated with B. subtilis one, when evaluated by their growth (20% more dry mass than negative control) and chlorophyll development (30% higher chlorophyll index than negative control) and in most parameters similar to the positive control, ethylenediamine-di(o-hydroxyphenylacetic acid). On average, Fe content was also higher in A. vinelandii-treated plants than on B. subtilis-treated ones. Results suggest that this new siderophore-based formulation product, prepared from A. vinelandii culture, can be regarded as a possible viable alternative for replacing the current nongreen Fe-chelating fertilizers and may envisage a sustainable and environment-friendly mending IDIC of soybean plants grown in calcareous soils.
Highlights
Iron (Fe) deficiency-induced chlorosis (IDIC) is a yield-limiting factor in an extensive range of crops worldwide (Hansen et al, 2006; Briat et al, 2015), especially severe in calcareous soils
The results found for the soil and plant analyzer development (SPAD) of stage 2 leaves along the 21 days after the treatment (Figure 3) are comparable to the SPAD data obtained by Martins et al (2018) and Ferreira et al (2019c) when synthetic siderophores [Fe(III)-azotochelin] or analogs thereof [Fe(III)-N,N′-dihydroxyN,N′diisopropylhexanediamide] chelates were tested as Fe sources to cucumber plants in hydroponic conditions and soybean (G. max) in calcareous soils, respectively
The effectiveness of B. subtilis ISS was comparable to the one registered for the negative control
Summary
Iron (Fe) deficiency-induced chlorosis (IDIC) is a yield-limiting factor in an extensive range of crops worldwide (Hansen et al, 2006; Briat et al, 2015), especially severe in calcareous soils. In the specific case of soybean culture, the incidence of Fe deficiency is increasing and potentially affects nearly two million hectares (Hansen et al, 2006). Commonly found in soil, due to its low solubility and dissolution kinetics, Fe availability for plants is very limited, especially in aerated alkaline and calcareous soils (Mengel, 1994; Shenker and Chen, 2005). Many crop yields are negatively affected and impaired by low Fe bioavailability in soils (Martins et al, 2017)
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