Keywords: Controlled release fertilizers, Slow release fertilizers, Nutrient use efficiency, Environmentally friendly fertilizers..

Anticipated benefits from slow release and controlled release fertilizers (SRFs/CRFs) are addressed through two main processes:

a) nutrient availability in the plant-soil system as affected by the interaction/competition between: plant roots, soil micro-organisms, chemical reactions and pathways for loss; and
b) matching nutrient release with plant demand.

The various aspects of fertilisation and environmental hazards associated with SRFs/CRFs and factors affecting nutrient use efficiency (NUE) are discussed in the light of these controlling processes.

Controlled and slow release fertilizers (CRFs and SRFs) in practical use are based either on slow decomposing/degrading organic-N compounds or on physically protected soluble fertilizers (matrix or coated forms). The release in case of the organic-N compounds is mainly due to microbial degradation and in some cases due to chemical decomposition. Thus it strongly depends on many soil factors such as: moisture content, wetting and drying, bio-activity, pH, and temperature. As a result, the release from such fertilizers is in many cases regarded as “slow”, rather than controlled due to its less predicted nature. Among the physically protected CRFs the granular fertilizers coated with organic polymers or resins offer good control over the release and can be tailor made to match the temporal nutrient demands of plants and required nutrient composition. The term “Controlled Release” is critically examined in the light of the agronomic and environmental implications of using the different CRFs or SRFs. Attention is given to relations between preparation methods, release mechanisms and the pattern and duration of release under field conditions. Emphasis is put on factors that improve nutrient use efficiency (NUE) and those that offer a much more environmentally friendly use of plant nutrients. Measures needed to further exploit the advantages offered by the CRFs and to increase their use in practice are analyzed and discussed.

Prof. Avi Shaviv, Water-Soil-Environment, Faculty of Agricultural Engineering, Technion-IIT, Haifa, Israel

36 pages, 108 refs.