Optimizing Agronomic Zinc Biofortification in Carrots

Abstract

Zn deficiency affects over 2 billion people globally, particularly in regions with Zn-deficient soils. Biofortification of staple crops offers a sustainable solution to this challenge. This study investigated Zn application methods (soil vs. foliar), rates (0-6 kg ha^-1), and timings (30, 50, and 70 days after sowing [DAS]) on growth, yield, and Zn accumulation in carrots under greenhouse conditions. Zn application significantly improved plant growth parameters, chlorophyll content, and yield. Chlorophyll content increased by approximately 36% as Zn rates increased from 0 to 6 kg ha^-1. Zn application at 6 kg ha^-1 increased carrot yield by 97.2% compared to the control. Foliar application achieved superior shoot Zn enrichment, with concentrations 51% higher than soil application at the highest rate. Root Zn concentrations showed no significant difference between application methods, suggesting distinct Zn translocation mechanisms between aerial and underground tissues. Early application (30 DAS) was most effective for root Zn accumulation, increasing concentrations by 175% compared to the control. An observed quadratic response to Zn application suggests an optimal threshold (6 kg ha^-1) for maximizing biofortification efficiency while maintaining economic feasibility. Early Zn intervention is essential for sandy soils with rapid nutrient leaching potential, and combined soil-foliar applications effectively address limited nutrient retention capacity. These findings demonstrate that Zn biofortification can simultaneously meet nutritional objectives and improve agricultural productivity in carrots, providing viable strategies for regions with similar soil constraints.

Keywords: Daucus carota L; Zn application methods; Zn biofortification; nutrient accumulation; time of Zn application; tropical agriculture.

FIGURE 1

Plant height (A) and chlorophyll content (B) over time as affected by Zn application rate and method. Effect of Zn fertilization rate on chlorophyll content of pot‐grown carrot (C); effect of timing of Zn fertilization on chlorophyll content of pot‐grown carrot (D). Error bars represent standard errors of the means.

FIGURE 2

Effect of Zn fertilization rate, time and method of application on shoot dry weight (A), root fresh weight (B), root length (C), and yield (D) of pot‐grown carrot. Error bars represent standard errors of the means.

FIGURE 3

Shoot Zn concentration of carrot plants grown in soil‐filled pots. Diagnostic plots were used to verify normality assumptions (A), effect of method (B), rate (C), and time (D) of Zn application. Figure 3C also shows the relationship between Zn application rate and shoot Zn concentration in carrots. The boxplots show the data distribution at each rate, where the horizontal line represents the median, the box represents the interquartile range (IQR), and whiskers extend to 1.5 × IQR. White diamonds indicate means. The red line represents the fitted quadratic regression (y = ax² + bx + c, R² = 0.85, p < 0.001).

FIGURE 4

Shoot Zn concentration of carrot plants grown in soil‐filled pots. Two‐way interactive effects: (A) application rate x method of application, (B) method x time of application, (C) application rate x time of application, and (D) rate × method × time of application. Error bars represent standard errors of the means.

FIGURE 5

Root Zn concentration of carrot plants grown in soil‐filled pots. Diagnostic plots were used to verify normality assumptions (A), the effect of rate (B), and time (C) of Zn application. Figure 5B also shows the relationship between Zn application rate and root Zn concentration in carrots. The boxplots show the data distribution at each rate, where the horizontal line represents the median, the box represents the interquartile range (IQR), and the whiskers extend to 1.5 × IQR. White diamonds indicate means. The red line represents the fitted quadratic regression (y = ax² + bx + c, R² = 0.85, p < 0.001). Figure 5D shows the two‐way interactive effect of application rate x time of application.