No exact figures are available for the production or use of manure in the country. Unofficial sources put the production of cattle and poultry manure at 31 million tonnes. It is estimated that about 30 percent of this amount is burnt as fuel by farmers who cannot afford other types of fuel. Out of the remaining 70 percent, part is just disposed of and the benefit of the nutrient and organic content is lost.
Currently some private companies are producing biofertilizers and compost. The municipal corporations of major cities too are involved in the production of compost and vermi-compost. There is no record of their production and sales.
In the context of increasing the yields of food crops by promoting balanced nutrient application, the production and application of biological fertilizers have been encouraged during the last four years. Three main private companies now produce biofertilizers. The main types of biofertilizers produced include: Thiobacillus (sulphur-oxidizing bacteria) along with zinc, Granulated Phosphate Solubilizing Bacteria and Azotobacter (a free living nitrogen fixer).
There are, however, distribution and marketing problems, especially in view of the limited shelf life of these materials. For example, one producer of Azotobacter inoculums produced two million one-kg packages of the material in three months, but unfortunately the company ran into problems of timely distribution and application. Another producer reports that more than 30 percent of its Azotobacter packages are still in the storage facilities of the company in Kerman.
Micronutrient deficiencies are a widespread health hazard, especially with regard to iron, vitamin A and zinc, particularly in developing countries.
The World Health Organization (WHO) announced in 1996 that the molar ratio of phytic acid to zinc (PA/Zn) should not exceed 25, otherwise the absorption through the digestive system of minerals, including zinc, contained in our diet, especially bread, becomes problematic. Three investigations on the level of body zinc among the young population in Iran indicate a serious problem of zinc deficiency. Research results indicate that a balanced application of nutrients (phosphate rates based on soil tests) and zinc sulphate on wheat fields lowers the PA/Zn ratio in the wheat grain and consequently improve the rates of absorption of minerals through the digestive system. Increasing the levels of grain phosphorus cause an increase in the phytic acid content. In general, unbalanced fertilization (high levels of phosphorus and low rates of zinc) increases the PA/Zn ratio while the application of zinc sulphate increases the concentration of zinc in the grain and decreases the level of phytic acid.
Investigations on the effect of zinc application on various wheat varieties have shown that, in addition to reducing the concentrations of phytic acid in the wheat grain, improved yields have been obtained.
To improve crop yield in the cultivated areas, gypsiferous soils must be supplied with sufficient micronutrients, particularly zinc. Among other options, utilization of mycorrhiza fungi or symbiotic bacteria, which do not need organic matter to survive, can be used to increase the amount of available P in such problem soils.
