THE ROLE OF ADDING HUMIC ACID AND IRON ON AVAILABILITY OF IRON AND MACRONUTRIENT (NPK) IN A CALCAREOUS SOIL PLANTED WITH WHEAT (TRITICUM AESTIVUM L.)

A pot experiment was conducted using calcareous soil with a loamy texture to investigate the role of humic acid in availability of iron and macronutrients (NPK) in soil.Six levels of humic acid were added: 0, 5, 10, 20, 30, and 40 kg ha-1 Wheat (Triticum aestivum L.) variety Abaa 99 was planted, iron was added at a rate of 11 kg Fe ha-1.NPK fertilizers were applied according to recommended fertilization practices.The experiment was designed in a completely randomized design (CRD) with three replications, and irrigation was performed with Tigris River water after 35% of the available water was depleted.Rresults showed that addition of iron fertilizer increased iron availability in soil.An increase in the availabile iron concentration in soil was also observed due to application of humic acid with NPK fertilizers and iron fertilizer.Addition of humic acid with iron fertilizer alone resulted in higher iron availability.Adding humic acid with NPK fertilizers significantly increased concentration of these elements in the soilbile Availabile nitrogen concentrations in soil significantly increased with the addition of humic acid, ranging from 50 to 97 mg Nkg-1 across the different treatments.A significant increase in availabile phosphorus concentrations was observed with addition of humic acid to all treatments, with values ranging between 38.66 and 68.15 mg Pkg-1.Addition of humic acid with iron fertilizer led to an increase in phosphorus availability in soil, with a positive correlation to the quantity of humic acid applied, ranging from 30.17 to 50.20 mg P kg-1.Addition of humic acid resulted in a