SPECIALITY FERTILIZERS

A balanced supply of essential plant nutrients is critical for successful crop production. Traditionally, farmers use a combination of conventional fertilizers such as urea for nitrogen, DAP (diammonium phosphate) or MAP (monoammonium phosphate) for phosphate, MOP(muriate of potash, i.e. KCl), SOP (sulphate of potash, i.e. K2SO4) for potash or compound fertilizers such as NPK’s for all three nutrients to grow their crops

During the crop season, however, nutrients can be lost to the groundwater, to the air and into the soil’s organic matter as a result of biological and physical activity in the soil.

These losses means that farmers don’t always fully benefit from the application of their fertilizers. Generally less than 50% of applied nitrogen, 20% of the phosphate and 10% of sulphur reaches the in crop in the first year of application.

The fertilizer Industry knows this and it has been the task of fertilizer industry agronomists to develop specialty fertilizers to avoid or reduce such nutrient losses for higher nutrient efficiency.

Current Market for Specialty Fertilizers:

In 1995/96, total worldwide consumption of controlled-release fertilizers was estimated to be 562,000 mt. The number increased to 700,000 mt in 1999, to 850,000 mt in 2001 and to about 1 million mt in 2005.

About two thirds of the controlled-release fertilizers are consumed in USA largely in Florida, California, Arizona and the Pacific Norwest where the high value of the horticultural crops, golf turf, nurseries and greenhouses justifies the additional costs of these fertilizers. Only 8-10% of such fertilizers are being used for high-value cash crops such as vegetables and fruits and almost none for commodity crops such as wheat, corn, soybeans and rice.

The main limitation of the use of these fertilizers in large hectare commodity crops has been the high cost of the coatings.

Currently, China has a capacity to produce about 500,000 mt controlled-release fertilizers for agricultural crops, although the actual production is well below the production capacity. It is estimated that China produces about 150-200,000 mt each year. of various types of controlled-released fertilizers. This represents only 1% of the total amount of fertilizers consumed in China.

What Are Specialty Fertilizers?

Specialty fertilizers can be classified into three general categories as:

1. Slow-release fertilizers where release rates are difficult to predict
2. Controlled-release fertilizers where release rates are predictable
3. Fertilizers associated with inhibitors of enzymatic processes

All three of these technologies have the potential to increase efficiency of the nutrients applied, generally resulting in higher crop yields.

1. Slow release fertilizers

The majority of slow -release fertilizers are materials with either sulphur or synthetic plastic coatings on the granular surface. The commonly used coated fertilizers are:

Sulphur-coated ureas (SCU). Sulphur-coated urea has long been popular and economical for incorporation and top-dressing of soils for high cash value specialty crops. The release rate is controlled primarily by the thickness of the coating and surrounding temperature. The sulphur in the coating is often an advantage because it lowers the pH of the medium.

SCU’s have two disadvantages:

1. The thickness of the sulphur coating means less fertilizer nutrient is delivered per tonne of product. eg. Urea is 45-0-0, i.e. it is 45% urea by weight. SCU is 35-0-0, i.e. it is 35% urea. The difference is the weight of the sulphur coating.
2. It is difficult to predict the release rate so these fertilizers have generally been used in the ornamental and turf market, i.e. for flowers and grasses father than for commodity crops such as wheat and corn.

2. Controlled Release (CR) Fertilizers

CR fertilizers use sophisticated polymer coating technologies to carefully manipulate nutrient release characteristics to meet the specific nutrient uptake needs of each crop. CR fertilizers can thus be “designer” fertilizers targeted to the specific crop and the particular climatic conditions. A golf course in Florida needs nutrients faster than one in the Rocky Mountains of Alberta simply because of its warmer temperature and longer day length.

To initiate release from polymer-coated materials, moisture must first diffuse through the coating and solubilize the fertilizer inside. Temperature is the key factor in the nutrient release from all of these products.

The key benefit of CR over Slow release fertilizers is the predictability of their nutrient release curve and thus these have the most potential for large hectare crops. Another key benefit is the thinness of the coating resulting in much higher nutrient content per tonne of fertilizer product.

Advantages of slow and controlled-release fertilizers

In the Northern Hemisphere, we plant the seeds in the cool, wet spring. The plant growths slowly over the next three to four months requiring different nutrients at different times during their growth period until the fall harvest.

Spring applied nitrogen fertilizers can be 100% available to the plant within weeks of planting but, of course, the plant is too young to take advantage. This exposes the nitrogen fertilizers to losses setting the stage for a lower plant yield and environmental contamination.

Slow release fertilizers are a great advantage over conventional soluble fertilizers because they can offer a complete nutritional package for a season or longer. Release rates vary from weeks to years depending upon the types of fertilizers and the environment where the crop grows.

• The planned release of nutrient from controlled release fertilizers better coincides with plant needs, minimizes nutrient losses and improves fertilizer use efficiency.
• Fertilizers need only be applied once at seeding instead of split applications over the growing season. This reduces labour, fuel and equipment costs plus reduces compaction of the soil.
• Seedling toxicity which is caused through high ionic concentrations resulting from the quick dissolution of conventional fertilizers is reduced.
• Larger fertilizer applications rates are possible because of the reduced toxicity and lower salt content.
• Evaporation losses of ammonia are reduced thus minimizing greenhouse gas problems.

3. Nitrification and Urease Inhibitors

Nitrification inhibitors are compounds that delay bacterial oxidation of the ammonium-ion (NH4) and nitrite (NO2) by depressing over a certain period of time the activities of Nitrosomonas and Nitrobacter bacteria in the soil. Nitrosomans oxidies ammonia to nitrite while Nitrobacter completes the oxidation of nitrite to nitrate (NO3) which is highly mobile in soils and the most available to the growing plant. The objective of using nitrification inhibitors is, therefore, to control leaching of nitrate by keeping nitrogen in the ammonia form longer, to prevent denitrification of nitrate-N and to increase the efficiency of nitrogen applied.

Urease inhibitors prevent or depress over a certain period of time the transformation of amide-N in urea to ammonium hydroxide and ammonium. They do so by slowing down the rate at which urea hydrolyzes in the soil, thus avoiding or reducing volatilization losses of ammonia to the air (as well as further leaching losses of nitrate).

They increase the efficiency of urea and nitrogen fertilizers containing urea (e.g. Urea ammonium nitrate solution UAN). Urease inhibitors thus inhibit for a certain period of time the enzymatic hydrolysis of urea, which depends on the enzyme urease.

Commercial urease Inhibitiors such as N-ServeTM were first commercialized by Dow Chemical in the mid-1990s but their use is not wide spread.

Advantages of nitrification inhibitors and urease inhibitors:

• Nitrification inhibitors through inhibition of nitrification of ammonia significantly reduce leaching losses of nitrogen and movement of nitrate into water supplies, while maintaining N availability to crops
• They also reduce emissions of N2O and NOx
• Nitrification inhibitors - indirectly - improve the mobilization and the uptake of phosphate in the rhizosphere
• Urease inhibitors may reduce ammonia volatilization losses particularly from top-dressed agricultural fields as well as under reduced tillage when urea is used as a source of nitrogen
• Urease inhibitors furthermore reduce seedling damage when seed-placed levels of urea/urea containing fertilizers are too high.

Future Outlook for Specialty Fertilizers in China

In China, the government and research institutions as well as the fertilizer industry are making tremendous efforts in the research and development of controlled-released fertilizer and other specialty products.

The consumption of controlled-released fertilizers and other specialty products in China is growing by 8-10% each year. The steady increase is driven partially by farmers’ desire to improve nutrient utilization efficiency and partially by the government initiatives to protect the environment quality.

The potential for increased use of controlled-released fertilizers and other specialty products is tremendous considering the advantages of:

• Labour and time saving because fertilizers need to be applied only once
• Increased nutrient recovery resulting in a higher Return on Investment for applying fertilizers
• Improved yields, and
• Reduced negative environmental impacts

However it is important to keep these fertilizers in perspective. The one million tonne of such fertilizers consumed in China represents less than 1% of the total fertilizer market in China.

Where in the western world, the high cost of labour is a key factor in the use of such fertilizers, in contract, China uses its low cost of labour as a competitive advantage.

Further, good specialty fertilizers cost considerably more than normal fertilizers. For Chinese farmers to adopt such fertilizers on a broad scale will require a significant economic benefit in the eyes of the farmer rather than in the eyes of the national planning organizations.