ARTICLE Guar gum based hydrogel as controlled micronutrient delivery system: Mechanism and kinetics of boron release for agricultural applications Nandkishore Thombare 1 | Sumit Mishra 2 | Reshma Shinde 3 | M. Z. Siddiqui 1 | Usha Jha 2 1 Processing and Product Development Division, ICAR-Indian Institute of Natural Resins and Gums, Ranchi, India 2 Department of Chemistry, Birla Institute of Technology, Ranchi, India 3 ICAR—RECR Farming system Research Centre for Hill and Plateau Region, Ranchi, India Correspondence Nandkishore Thombare, Processing and Product Development Division, ICAR-Indian Institute of Natural Resins and Gums, Namkum, Ranchi 834010, India. Email: nandkishore.icar@gmail.com Funding information Indian Council of Agricultural Research Abstract A boron loaded super-absorbent hydrogel (BLSAH) was developed through in situ incorporation of boron (B) in a guar gum-based hydrogel and characterized with FTIR, thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and swelling studies, showing maximum absorption up to 356 g/g. The release pattern of B from the BLSAH and its kinetics was studied in water as well as soil. The B release pattern of the BLSAH was also compared with the commercial B fertilizer, boronated single super phosphate (bSSP). The BLSAH, following the Fickian mechanism, released 38% B, as compared with 51% of the bSSP, during the incubation period of 30 days in soil. The half-life period for the BLSAH (96.25 days) in soil was almost triple that of the bSSP's half-life (33.32 days), which is indicative of the slow and controlled release of B from the BLSAH. Thus, owing to its sustained nutrient release ability, the syn- thesized BLSAH exhibited wide potential for applications in agriculture sector. KEYWORDS acidic soils, agriculture, boron, guar gum, superabsorbent hydrogel 1 | INTRODUCTION Boron (B) is one of the essential micronutrients, required for normal growth, development, yield and quality of crops. [1,2] It also plays a vital role in essential metabolic processes in plants, including structural and functional integrity of the cell wall and membranes, cell division and elongation, lignification, sugar transport, nitrogen and carbohydrate metabolism, ribose nucleic acid (RNA) metabolism, respiration, indole acetic acid (IAA) metabolism, phenol metabolism, pollen germination and fertilization, transport of potassium (K), stomata opening, drought tolerance, and so on. [3–5] B deficiency is one of the major constraints to crop production, limiting nutrient use efficiency and crop yield, [6] and has been reported in more than 80 countries and for 132 crops over the last 60 years. [7] B deficiency results in considerable reduction of yield in annual cereal, legume/pulse, oilseed and perennial crops. [5,8] B deficiency is widespread in highly leached acid soils rich in alu- minum (Al) and iron (Fe) oxides, alkaline/calcareous soils, and light or coarse-textured soils in many countries and has been realized as the second most important micronutrient constraint in crops after that of the zinc on global scale. [6,9] The critical limit for boron's minimum requirements and toxicity for crops is narrower than any other nutri- ent element, [5,10] hence plants can experience both B deficiency and B toxicity in a single growing season. [11] B deficiency often creates disturbances in the growth of plants, including undersized and cracked fruits and leaf fall. [12] Worldwide, around 30% of the arable soils are acidic. [13] In acidic soils of high rainfall area, due to extensive leaching of clay minerals, the proportion of Al and Fe oxides increases and this results in fixation of soluble form of B, especially, H 2 BO 3 - , leading to B deficiency. [14,15] Thus, it appears to be an important area of research to tackle the challenge of managing B nutrition in agriculture, especially in such problematic soils. Received: 9 November 2020 Revised: 6 January 2021 Accepted: 6 January 2021 DOI: 10.1002/bip.23418 Biopolymers. 2021;e23418. wileyonlinelibrary.com/journal/bip © 2021 Wiley Periodicals LLC 1 of 10 https://doi.org/10.1002/bip.23418