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

12.2. Plant health
Fertilizer use at excessive rates has
deleterious effects on crop growth. Examples are
the lodging of cereals and the low sugar content
of sugar beet resulting from excess quantities of
nitrogen, nutritional disorders involving trace
elements such as zinc due to excessive phosphate
fertilizer and lime; impeded seed germination
and seedling injury from too much soluble
fertilizer salt adjacent to the seed row; the
acidifying action of nitrogen fertilizer on soil, and
increased incidence of plant and pest attacks with
excessive nitrogen fertilizer. If the nitrogen
application leads to acidification of the soil, it can
induce aluminum and manganese toxicity if
compensating lime is not applied.
As regards crop diseases, the most important
impact of nitrogen is on vigour and plant growth.
These two factors have an important impact on
plant susceptibility to many diseases. Vigorous
plants with rapid growth are generally more
sensitive to obligate parasites and some
pathogens are specifically more aggressive
towards vigorous plants. However, most of the
necrotic pathogens attack less vigorous plants
with nitrogen deficiency. Balanced fertilization
provides excellent protection. The time of
application of fertilizers is important. A wrong
timing may induce substantial growth of foliar
parts of plants and maintain high humidity
conditions in the crop canopy which are
favorable to disease development.
Phosphorus application seems to favour plant
protection against diseases, either by correcting a
deficiency in soil phosphorus, and thereby
inducing a better growth of the plant, or by
speeding up the maturation process, disfavoring
some pathogens like downy mildew that effects
the young tissues.
Potash can increase the efficiency of use of
other nutrients by plants, particularly of N. Potash
has a beneficial effect on the quality of a wide
range of crops, especially in terms of improved
protein quantity and quality. Potash can decrease
the incidence of plant diseases and reduce abiotic
stresses, particularly cold stress. The element may
have a direct action on pathogen penetration,
lesion size and on inoculum density. An indirect
effect of potassium on disease development is to
stimulate the healing process (interaction with the
scar parasites), to increase the resistance to cold,
and also to delay the maturity and senescence of
fruits. There is no known pollution or health
hazard due to the use of potash fertilizers in
agriculture. However, the application of
potassium chloride to chloride-sensitive crops
should be avoided, as should its use on certain
saline soils.
Calcium may have an effect on the cell wall of
plants by making them more resistant to
pathogen penetration. A deficiency in calcium
increases the sensitivity of plants to many fungi.

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Mineral Fertilizer Use and the Environment