Eco-Friendly Iron-Humic Nanofertilizers Synthesis for the Prevention of Iron Chlorosis in Soybean (Glycine max) Grown in Calcareous Soil

Abstract

Iron deficiency is a frequent problem for many crops, particularly in calcareous soils and iron humates are commonly applied in the Mediterranean basin in spite of their lesser efficiency than iron synthetic chelates. Development and application of new fertilizers using nanotechnology are one of the potentially effective options of enhancing the iron humates, according to the sustainable agriculture. Particle size, pH, and kinetics constrain the iron humate efficiency. Thus, it is relevant to understand the iron humate mechanism in the plant–soil system linking their particle size, characterization and iron distribution in plant and soil using 57 Fe as a tracer tool. Three hybrid nanomaterials (F, S, and M) were synthesized as iron-humic nanofertilizers ( 57 Fe-NFs) from leonardite potassium humate and 57 Fe used in the form of 57 Fe(NO 3 ) 3 or 57 Fe 2 (SO 4 ) 3 . They were characterized using Mössbauer spectroscopy, X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), transmission electron microscopy (TEM) and tested for iron availability in a calcareous soil pot experiment carried out under growth chamber conditions. Three doses (35, 75, and 150 μmol pot -1 ) of each iron-humic material were applied to soybean iron deficient plants and their iron nutrition contributions were compared to 57 FeEDDHA and leonardite potassium humate as control treatments. Ferrihydrite was detected as the main structure of all three 57 Fe-NFs and the plants tested with iron-humic compounds exhibited continuous long-term statistically reproducible iron uptake and showed high shoot fresh weight. Moreover, the 57 Fe from the humic nanofertilizers remained available in soil and was detected in soybean pods. The Fe-NFs offers a natural, low cost and environmental option to the traditional iron fertilization in calcareous soils.

Recent Developments in the Application of Nanomaterials in Agroecosystems

“…These types of fertilizers can also be prepared by the encapsulation of nutrients within the nanomaterials [31][32][33]. Nano-fertilizers can improve the yield and quality of crops with increased nutrient usage efficiency, while lessening the production cost and thereby resulting in a sustainable agriculture [34][35][36][37][38]. The use of pesticide is a common practice in agriculture and several studies have been carried out for the advancement of effective pesticides [39][40][41][42].…”

Application of Nanotechnology Solutions in Plants Fertilization

“…The plants fertilized with the leonardite humates accumulated slightly higher fresh weight than those fertilized with the iron chelate, the humic substances generally increase the shoot and root growth by 15-25% and the accumulation of total iron in pods for soybean plants reaches 50 mg/kg under conditions of sufficient nourishment [41]. The applied nanoparticles of Fe 57 were capable to supply the Fe 57 deficiency in plant and it was transported from root to shoot and reaches the pods, this iron humate was prepared taking into account its maximum complexing capacity in order to avoid the iron flocculation in calcareous conditions [41]. As a remark, in the context of sustainable agriculture, the Fe-nanoparticles can be considered as a part of novel technology in line with the politics of precision and sustainable agriculture.…”

“…However, the effect of an organic shell around nano-Fe made these nanoparticles more compatible for entering and translocation in the plant [40]. Another direction to suppress iron deficiency common in human diet is to use iron fertilizers based on humic substances extracted from lignites, such as leordine, it is stated [41] that this kind of fertilizer is more ecofriendly than synthetic iron chelates as discussed above, but they are less efficient in suppressing iron chlorosis. Low concentrations of superparamagnetic Fe-nanoparticles increased significantly the chlorophyll contents in sub-apical leaves of soybeans under hydroponic conditions.…”

Which Traits of Humic Substances Are Investigated to Improve Their Agronomical Value?

“…This conformational change is likely to tune the plant Fe nutrition and HS ability to penetrate plant roots [ 43 ]. Owing to these reasons, artificial Fe was even added to coal HSs to boost plant stimulation and Fe nutrition in alkaline soils [ 44 ]. Therefore, inherent metallic substances beneficial for plant nutrition should be assessed to differentiate coal-derived HSs from other types of HS.…”