Continuous Organic and Inorganic Sources of Nutrients Addition Impacts Yield and Fe and Mn Concentrations in Maize and Soil

ABSTRACT

Soil micronutrient deficiency, particularly of iron (Fe) and manganese (Mn), is a major global agricultural challenge adversely affecting crop productivity and human nutrition. With conventional water‐soluble fertilizers having abysmally poor use efficiency, alternate nutrient management options, including use of organic nutrient sources, need to be explored for managing Fe and Mn deficiency in soils and achieving sustainable crop production. The present study was carried out to assess the long‐term (20 years) effect of different nutrient management modules on maize ( Zea mays L.) yield, Fe and Mn uptake, and transformations in Vertisols. The study included 12 treatments comprising various combinations and levels of nitrogen (N), phosphorus (P), and potassium (K) applied through inorganic sources (based on general recommendations and soil test crop response [STCR] equations), organic sources (including Gliricidia sp. loppings, maize residues, farmyard manure [FYM], poultry manure, and urban compost), and through an integrated approach combining both organic and inorganic inputs. The combined application of FYM at 5 Mg ha ⁻¹ along with 75% NPK based on STCR resulted in the highest maize yield (6.33 Mg grain ha ⁻¹ , 7.07 Mg stover ha ⁻¹ ) and total uptake of Fe (3901 g ha ⁻¹ ) and Mn (443 g ha ⁻¹ ). Sole or integrated use of inorganic and organic sources of nutrients significantly increased soil organic carbon (5.37–8.94 g kg ⁻¹ ) compared to the control (no addition of nutrient sources) (4.99 g kg ⁻¹ ). The highest DTPA‐Fe concentration (9.56 mg kg ⁻¹ ) was observed under the Gliricidia loppings (2 Mg ha ⁻¹ ) + maize residues (5 Mg ha ⁻¹ ) + poultry manure (1 Mg ha ⁻¹ ) treatment, while the highest DTPA‐Mn content (12.8 mg kg ⁻¹ ) was obtained with partial substitution of STCR‐based NPK using urban compost (5 Mg ha ⁻¹ ). Regression analysis revealed that DTPA‐Fe content explained 24% variability of grain Fe concentration, whereas DTPA‐Mn explained 42% variability of grain Mn concentration. In this soil, there were diminishing returns in grain Fe concentration as soil DTPA‐Fe increased beyond 8.665 mg kg ⁻¹ . Whereas DTPA‐Mn content continued to influence grain Mn concentration in a nearly linear fashion. The available Fe and Mn fractions (water‐soluble and sorbed) were highest under high organic manure application (20 Mg FYM ha ⁻¹ year ⁻¹ ). The residual Fe (~98.3%–98.9%) and Mn (~40.7%–56.7%) fractions comprised the major share of soil Fe and Mn, respectively, under various treatments. Path analysis revealed the dynamic inter‐conversion among soil Fe and Mn fractions to replenish the available pools and maintain Fe and Mn crop uptake. The generated information could be used for devising efficient Fe and Mn management strategies of the maize crop in the study area.