Although awareness of the importance of micronutrients for plant, animal and human health has spread considerably around the world in the past few years, deficiencies remain all too prevalent. There are eight principal micronutrients that are essential to plant growth and health: manganese (Mn), boron (B), copper (Cu), iron (Fe), chlorine (Cl), cobalt (Co), molybdenum (Mo) and zinc (Zn). Although they are only present in very small quantities, they are all necessary. They occur in crops all over the world, but certain species or varieties are more sensitive to deficiencies than others, and this is proving a potentially limiting factor in making further gains in global food security. Thus, maize can be highly sensitive to Zn deficiency, sunflowers to B, and wheat to Cu. Table 1 shows the susceptibility of certain major food crops to six key micronutrient deficiencies.
Even crops with a relatively low susceptibility to a particular micronutrient can become deficient when its available concentration is very low. (New Ag International, June 2006, p56.) Thus, in the Middle East, there is widespread Zn deficiency in wheat, even though this crop is considered to be relatively tolerant to Zn deficiency.
Soil factors can cause micronutrient deficiencies in crops. These include:
* Cultivating poor sandy soils with low micronutrient contents.
* High soil pH levels can have a negative effect on micronutrient availability.
* High salt content can adversely affect micronutrient uptake.
* A high CaC[O.sub.3] content in the soil.
* Failure to add micronutrients to the soil in the wake of intensive cultivation.
Other adverse factors may include an unbalanced application of N fertilizers and antagonisms between micronutrients, in 1990, the FAO studied micronutrient deficiencies in Finland and 14 developing countries. The overall frequency of micronutrient deficiencies ranged from Zn (49%), B (24%), Mo (15%), Cu (14%), Mn (10%) and Fe (3%). In Mexico, it was found that B and Zn deficiencies were the most common, affecting about 50% of the sites evaluated. In Egypt, significant micronutrient deficiencies were found in all major crops, as shown in Table 2. (Micronutrients in Soils and their Role in Plant, Animal and Human Health, Mohamed M. El-Fouly, Fertilizer Technology Department, National Research Centre, Cairo. Paper presented at AFA Annual Conference, February 2006.)
Zinc deficiency appears to be the most widely occurring micronutrient deficiency in the world, being most evident in maize, rice, beans, cotton, coffee, citrus, apples and wheat. The problem is most acute in areas with strongly leached tropical, sandy, calcareous, alkaline and flooded soils. Areas with severe Zn deficiencies include the entire Middle East, India, much of South East Asia, Western and Eastern Australia, Mexico and eastern Brazil. In India and …