Th ere is a very large range of micronutrient fertiliser products in the world but their distribution and aff ordability varies with geographical regions. In South Asia, for example, improvements in crop yields are being achieved by the incorporation of micronutrients in new fertiliser blends using traditional technology. In developed countries, research over the past two decades has led to the diversifi cation of foliar fertiliser products and speciality fertiliser formulations for specifi c crops. New products are being considered for overcoming micronutrient disorders in aerobic rice and for reducing deleterious impacts of fertilisers in the environment.
Zinc defi ciency continues to impair grain production in South Asia (Chapters 1 and 4). Presently, the best option to deliver Zn to fi eld crops is to incorporate Zn with the macronutrient fertilisers available in the region. Accordingly, the fertiliser industry is exploring marketing zincated urea (Shivay et al., 2008). A new technique for coating urea with ZnO was recently developed by Suri (2005).
Th e development of suspension concentrates, based on sparingly soluble inorganic micronutrient sources (Moran, 2006), is the single most signifi cant advance in technology to occur in recent times, and it has resulted in a wide range of improved products for growers. Research continues into developing products that combine nutrients with agrichemicals, and also new surfactants and dispersants for improved fl occulation and performance of products on leaf surface.
Iron defi ciency remains the most diffi cult and expensive micronutrient defi ciency to control (Fernández and Ebert, 2005), and the incidence of defi ciency is increasing in rice production in particular. Th e use of organic materials is being tested to determine if the effi cacy of current Fe products can be improved for aerobic rice (Pal et al., 2008) and other crops. New chelated-Fe products are also being evaluated (Lucena et al., 2008). Since EDTA has low biodegradability and persists in the environment, new biodegradable chelating agents are desirable. One that is showing some promise is imidodisuccinic acid (Lucena et al., 2008).
Runoff resulting from the deployment of highly water-soluble fertilisers can reduce the environmental quality of waterways. Some governments are legislating to phase- out the use of some traditional fertilisers, including highly water-soluble phosphatic fertilisers. Gillman and Noble (2005) propose supplying nutrients on hydrotalcite and bentonite platforms for these situations. In the future, there is likely to be greater research eff ort into the development of alternative fertilisers with less environmental impact.
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In conclusion, although a diverse array of micronutrient fertilisers is manufactured around the world, micronutrient disorders remain problematic for many growers. Whilst there remains a need to target fertiliser development for Fe defi ciency in alkaline and calcareous soils, and to develop longer lasting forms of B fertiliser, greater emphasis is required to share existing knowledge and products with growers (Chapter 4, 5, 6, 7).
Distribution of micronutrient products to small farmers
Th e adoption of micronutrient fertilisers by farmers has varied markedly among diff erent countries. In Turkey, for example, within the space of 12 years, Zn fertiliser use has increased from zero to 350,000 tonnes annually. Th e rapid expansion in use of Zn followed several years of comprehensive research, which demonstrated large increases in yield from Zn fertiliser use, particularly in the main cereal, wheat. However, in China, despite a nationwide soil study, which demonstrated widespread problems with low microutritent levels, backed up by extensive fi eld experiments showing crop yield increases, more than 20 years later the incidence of low micronutrient levels appeared to be unchanged (Jin et al., 2006).
Many other cases can be cited, particularly in developing countries where clear evidence of the existence of micronutrient defi ciencies and crop responses with high benefi t:cost ratios from micronutrient fertiliser use, are not matched by widespread adoption. Questions need to be asked about the causes for failure to successfully extend the technology to farmers, and failure of the market to develop and supply products that would seem to have benefi cial eff ects on crop production.
Small farms require small amounts of micronutrient fertilisers and, hence, there is a need to market products that meet their needs. In South Asia, for example, a small farmer may manage less than 1 ha, and if growing a pulse crop on half of the fi elds, she/he would need a few hundred grams of Mo fertiliser to correct Mo defi ciency. Small farmers are unlikely to buy extra Mo and store it for use over a few years. Unless Mo is available in the market in quantities comparable to what the farmer needs, they are unlikely to purchase Mo.
Developments in micronutrient products and research include:
• production of pelletized slow-release B from calcinated colemanite (Flores et al., 2006);
• combining humic acid with B sources into a granulated product;
• incorporation of a wider range of Zn complexes or chelates into macronutrient fertilisers;
• encapsulation of water-soluble micronutrients in hydrogels and other smart polymeric materials;
• incorporation of micronutrients into polymeric phosphates (Ray et al., 1997; Bandyopadhyay et al., 2008);
• incorporation of micronutrients into fl uid fertilisers for alkaline and calcareous soils; and
One strategy being explored to overcome this problem in Bangladesh is to apply even smaller amounts on the seed, to further decrease the cost of fertiliser. However, the problem of supplying small quantities in the market, when needed by farmers, remains. If only 10-15 g Mo/ha is required, how can this be packaged and distributed in a profi table manner for those involved in the market chain, while still being aff ordable to a small farmer? When the real costs of packaging and distribution of small amounts of micronutrient fertiliser are calculated, the benefi t:cost ratios estimated from experimental data are probably over-optimistic, and this may explain the market failure.
Th is suggests that new application, packaging and distribution strategies are needed for the reliable supply of micronutrient fertilisers into markets where there is clearly market failure, despite evidence for demand and of a substantial yield benefi t. Enrichment of N, NPK or P fertilisers with micronutrient fertilisers is used in many countries. Th is results in more expensive NPK fertiliser, but reduces other costs of distribution and supply. It also reduces the risk to consumers of buying spurious Zn fertiliser products in unregulated markets (Shivay et al., 2008). Firstly, fewer products need to be handled in the market and this makes it easier for local traders to have product in stock when needed. Secondly, it reduces the complexity for small growers using micronutrients. It cuts out the need for mixing and application of small amounts of micronutrient fertiliser.
When the NPK or P fertiliser is enriched at the correct level, alleviation of micronutrient defi ciency is assured. However, it is important for advisers and traders to be aware of the likely poor results when NPK fertiliser, without micronutrient enrichment, is inadvertently supplied in the market. Th e strategy to use enriched NPK fertiliser will result in limited residual benefi t in following crops because the amounts supplied are generally smaller than with application of micronutrients alone. Hence, the micronutrient defi ciency is treated only in the crop that is fertilised, and repeated additions will be needed. On the other hand, accumulation of excess, leading to toxic levels in the soil, is minimal when micronutrient-enriched fertiliser is used.