Organic agriculture enhances zinc concentrations in edible crop parts: A meta-analysis

Abstract

Context

Zinc (Zn) and iron (Fe) are essential micronutrients for humans, and their deficiencies lead to widespread malnutrition and other related health problems. Organic agriculture is often promoted for its potential to enhance soil health and environmental sustainability, but its effects on Zn and Fe concentrations in crops have remained inconsistent.

Objective

This meta-analysis aimed to compare Zn and Fe concentrations, and also evaluated crop yield, between organic and conventional agriculture systems. It also sought to identify environmental and agronomic factors that influence these outcomes.

Methods

A total of 322 paired data points from 54 peer-reviewed publications on cereals, legumes, and vegetables were analyzed. The natural logarithm of the response ratio (lnRR) was employed as the effect size for Zn and Fe concentrations in edible crop parts and crop yield. The influences of crop type, soil properties (soil texture, soil organic carbon, soil pH) and climate factors (climate region, annual mean air temperature, annual precipitation) on the effect sizes were assessed using a mixed-effects model.

Results and conclusions

Zinc concentrations in organically grown crops were 14.2 % (95 % CI: 9.7 – 19.0 %, p < 0.001) higher than those under conventional agriculture, with the effectiveness being more evident in vegetables. This increase corresponded to an average of 4.3 mg kg^-1 higher Zn concentrations across crop types. Iron concentrations did not show an overall difference between the two systems, only under wet conditions (annual precipitation > 850 mm) where organically grown crops had 14.5 % (95 % CI: 3.57 – 26.66 %, p < 0.001) higher Fe concentration than conventionally grown crops. Despite these effects on micronutrients, organic agriculture was associated with a 24.7 % (95 % CI: −31.2 to −17.6 %, p < 0.001) reduction in crop yield, especially for cereals grown in arid regions. These findings underscore a critical trade-off between nutritional micronutrient concentration and crop productivity.

Significance

This is the first meta-analysis comparing organic and conventional agriculture regarding their impacts on micronutrient availability in crops. The findings highlight the need for integrated agronomic strategies that optimize nutrient quality while maintaining productivity. Bioavailability was not assessed in the present study but is highlighted as an urgent research priority when examining how organic systems influence micronutrient bioavailability for human consumption.