Effect of iron-chelated humic acid on maize growth, yield and iron biofortification in calcareous soil

Abstract

Abstract In alkaline calcareous soils, iron (Fe) deficiency is common and can restrict crop production and the nutritional quality of grain due to reduced Fe solubility and plant availability under high pH and CaCO 3 . Chelation of Fe sources such as iron sulfate (FeSO 4 ) and iron chloride (FeCl 2 ) with humic acid (HA) helps to improve Fe availability in soil via formation of stable HA-Fe complexes; however, its efficiency in alkaline calcareous soils remains poorly explored. In this regard a field experiment was conducted where Fe-chelated HA was investigated for its potential to enhance soil Fe availability, maize productivity, and Fe biofortification in grain. The study was conducted in the kharif season 2023 under a factorial randomized complete block design with three replications. Four Fe and HA treatments [sole FeSO 4 , untreated HA, HA chelated with FeSO 4 (HA-FeSO 4 ), and HA chelated with FeCl 2 (HA-FeCl 2 )] were evaluated through three application strategies (AS): seed priming with a 0.5% solution, foliar application (0.5% solution), and soil application at 10 kg ha − 1 .Results demonstrated that, HA-FeSO 4 produced the highest values for AB-DTPA extractable Fe (7.42 mg kg − 1 ), grain Fe (79 mg kg − 1 ), biological yield (11,990 kg ha − 1 ), grain yield (4867.5 kg ha − 1 ), and stover yield (7789.7 kg ha − 1 ) compared to other Fe sources. Among AS, soil application gave the highest soil mineral N (27.8 mg kg −1 ) and total N (0.577 g kg − 1 ). HA-FeSO 4 combined with soil application (Fe sources x As) resulted in optimum stem total N (3.49 g kg − 1 ), leaves total N (4.48 g kg − 1 ) and grain total N (23.23 g kg − 1 ). From these findings, it was concluded that Fe amendments with proper AS can stabilize Fe in plant-available forms, improve nutrient uptake, maize production, and grain nutrition. Thus, soil-applied HA-FeSO 4 is a promising and effective strategy for promoting soil fertility and maize performance in alkaline calcareous soils and could be investigated further in multi-season trials to evaluate its long-term agronomic and economic feasibility.