Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

9.3.1. Slow release fertilizers
Controlled release nitrogen fertilizers have
agronomic advantages, especially in tropical
regions, and in regions with light-textured soils
and under heavy rainfall or irrigation, where N
losses are particularly large. However, to date the
cost of slow-release fertilizers has limited their
use to high value crops such as vegetables.
The use of controlled release nitrogen
fertilizers on field crops is most advanced in
Japan, on rice, whose production is heavily
subsidized. The amount of fertilizer required by
rice is commonly applied in 3 to 4 applications.
This is labour intensive and in order to reduce
the number of applications, coated slow-release
fertilizer have been studied. Experimental results
so far have indicated that a single application of
the whole amount of coated fertilizers in a basal
application gives yields comparable to those with
traditional split applications. Also the efficiency of
nitrogen use could be improved by 10% to 20%
due mostly to an increase of about 16% in the
plant uptake of N.

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Mineral Fertilizer Use and the Environment
9.3.2. Nitrification and urease
inhibitors
Environmental restrictions in certain developed
countries may encourage more farmers to use
nitrogen or urease inhibitors in association with
nitrogen fertilizers in areas where it is essential to
reduce losses for environmental reasons. The
application of urea (or a urea/ammonium nitrate
solution, UAN) amended with a urease inhibitor
would generally permit a substantial reduction in
nitrogen losses to the atmosphere, and
consequently also in the application rates, without
affecting growth and yield of fertilized crops.
The future, and in particular the wider use of
slow or controlled release fertilizers, and
nitrification and urease inhibitors primarily
depends on the development of new, effective,
low-price and non-toxic products. Even if
promising new products were developed, due to
lengthy, time-consuming tests and data collection
for registration purposes, the introduction to the
market would take several years. It should also be
taken into account that giving advice to farmers
on how to use them correctly would be very
expensive.
The whole question of controlled release
fertilizers, nitrification and urease inhibitors, is
dealt with by in detail by M.E. Trenkel (1998).