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Enriched fertiliser to fight zinc deficiency

Work is underway to improve the nutritional content of staple crops to tackle malnutrition (© Neil Palmer (CIAT))
Work is underway to improve the nutritional content of staple crops to tackle malnutrition
© Neil Palmer (CIAT)

'Hidden hunger' - the lack of essential micronutrients in the diet, such as iron (Fe), zinc (Zn) and Vitamin A - is a growing global concern, and a major cause of child mortality and mental impairment. Every year, an estimated 400,000 children, predominantly in Asia, die from zinc deficiency alone, nearly as many as die from malaria. Symptoms include diarrhoea, poor growth, and weaker resistance to infections such as pneumonia. But increasing micronutrient concentrations in grain through the use of specially enhanced fertilisers could be a fast and cost-effective way to improve nutritional health among cereal-dependent communities.

Currently, nearly 50 per cent of global cereal production takes place on land with inadequate levels of soil-available zinc, reducing crop yields as well as contributing to poor child health and high mortality rates. In the past, little research attention has been given to enrichment of cereals grains, but biofortification of staple crops with target micronutrients (zinc, iron and Vitamin A) is now a key focus for the Consultative Group on International Agricultural Research (CGIAR), through its HarvestPlus programme.

Adding zinc oxide (ZnO) or zinc sulphate (ZnSO4) to a standard (NPK) fertiliser, for example, boosts grain yields in rice and wheat, with ZnSO4 also significantly enhancing Zn concentration in the grain. Increasing micronutrient levels in the soil, through enriched fertilisers, is recommended as the quickest and most locally-appropriate way to enhance Zn uptake by plants and people, simultaneously improving crop yields and dietary Zn levels.

Zinc-enrichment in Asia

Adding zinc to a standard fertiliser, boosts grain yields in rice and wheat, and enhances zinc concentration in the grain (© FAO/Ahmed Ouoba)
Adding zinc to a standard fertiliser, boosts grain yields in rice and wheat, and enhances zinc concentration in the grain
© FAO/Ahmed Ouoba

In Central Anatolia, Turkey, use of Zn-enriched soil and foliar fertilisers has been carried out since the mid-1990s. Farmers using the enriched fertilisers have more than doubled the Zn concentration in their grain, and generated significant increases in plant growth and grain yield, worth an estimated US$100 million per year. In India, use of Zn-enriched urea (ZEU) has been found to boost grain yield in rice and wheat, and to offer a 60 per cent increase in Zn concentration. Other non-dietary benefits from high Zn concentration in grain include: better seed viability and vigour, allowing for a reduced seeding rate; improved stand establishment in marginal lands; and greater tolerance to environmental stresses during early growth stages.

For resource poor families, consumption of sufficient micronutrients is often compromised by high food prices, with Zn deficiency in locally-grown grain compounding the problem. In this situation, use of Zn-enriched fertiliser could be very cost effective: applying 2-3 kg/ha has been found to bring an increase in yields worth double the value of the fertiliser applied. In addition, soil-applied zinc sulphate remains effective for two to three years, bringing residual benefits for later crops. In Pakistan's wheat-rice system, for example, applying ZnSO4 in wheat crops has significantly increased grain yields in subsequent rice crops. Virtually no toxicity is documented in Zn-treated soils, but periodic soil monitoring is recommended, in order to prevent over-dosing and damage to the environment.

International recognition

Biofortification of staple crops with target micronutrients is now a key focus for the CGIAR (© Neil Palmer (CIAT))
Biofortification of staple crops with target micronutrients is now a key focus for the CGIAR
© Neil Palmer (CIAT)

The successful use of Zn-enriched fertiliser in Turkey has been highly praised by the International Fertiliser Industry Association, which in 2005 recognised lead Turkish researcher, Dr Ismail Çakmak with its International Crop Nutrition Award. An IFA press release notes, "The Anatolia initiative is one of the world's first examples of using agricultural practices to address public health problems as well as improved crop production, and its success provides a model for countless other nations. More soils throughout the world lack zinc than any other micronutrient. About 50 per cent of the world population suffers from iron and zinc deficiencies, which can be addressed through this cost-effective method."

While increasing Zn concentration in grain through fertilisers has clear benefits for crop yields and human diets, the progeny of such grain do not maintain these high Zn levels in either foliage or seed. Crop gene pools exhibit a wide variation, both in terms of micronutrient content and the availability of those nutrients for absorption by the body. Achieving permanent, plant-based improvement in Zn concentration is possible, but demands a long term breeding programme, as is being pursued by HarvestPlus. In the meantime, policymakers should prioritise the adoption of Zn-enriched fertilisers, as well as complementary strategies such as food fortification.

Written by: Hafeez ur Rehman

Date published: May 2011

 

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