A team from the Department of Agronomy at the University of Córdoba (UCO) in Spain has demonstrated, through field tests carried out during eight agricultural seasons, that foliar application with fertiliser increases the concentration of zinc in wheat, more than if it is applied to the soil.
Micronutrient deficiencies pose health problems for a third of the world's population.
Worldwide, zinc deficits are more problematic in rural areas of developing countries, where diets are largely limited to vegetable products grown in soils suffering from low nutrient availability.
Biofortification, the process of bolstering the nutritional value of crops by increasing the concentration of vitamins and minerals in them, has arisen as a remedy for this problem.
Research by UCO
In the search for solutions, a unit within the Department of Agronomy at the University of Cordoba (DAUCO), headed by the researcher Antonio R. Sanchez Rodríguez, has spent eight years searching for the best biofortification strategy in terms of applying zinc to wheat grown in calcareous soils in southern Spain.
Between 2012 and 2019, the team tested different methods to biofortify wheat in 11 field trials in zinc-deficient soils.
The effects of applying different doses of fertiliser to the soil (up to 10kg/ha) were evaluated, in addition to the results of applying different doses of zinc by spraying the plant at various stages of the wheat's growth.
Results of foliar application
While application to the soil was not very effective, foliar application, or feeding, was shown to be a very efficient strategy to increase the zinc content in plants, "augmenting the concentration in grains up to 50%", according to the researchers.
Foliar application was shown to be much more effective, because with just one tenth of the product (1.28kg/ha), better results were obtained than when applied to the soil.
Taking into account the variety of wheat, this direct application to plants was more effective after the start of growth or during flowering.
It indicates that nourishing the plant itself, and not the soil, was an effective way to tackle the problem of zinc deficits in calcareous soils in the short-term.
In addition, if at some point wheat was purchased based on its nutritional content, growers could see increases in their profits.
Zinc-deficit areas
This solution "is very valuable for places where there is no other source of zinc in diets, although it would entail adding another task to wheat cultivation, or combining it with the application of other phytosanitary treatments", noted Sanchez.
On this project the team also looked for a soil indicator that would help predict the response of durum wheat to zinc fertilisation, in terms of its yields.
However, they found that conditions in the field make it very difficult to verify this, and that a simple indicator cannot predict this response.
While at the laboratory level some indicators could be defined, researchers said that in the field this task is difficult, since it is highly dependent on factors such as precipitation, and would require many more years of study.
