Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
low placement of LEPA nozzles) for control of spider mite in corn . However, for shoot
borer spray should reach above ear region
• Insecticide level must specially state that the product can be applied through irrigation
system
Selection of Fertilizers
Effective fertigation requires an understanding of plant growth behavior including nutrient
requirements and rooting patterns, soil chemistry such as solubility and mobility of the nutrients,
fertilizers chemistry (mixing compatibility, precipitation, clogging and corrosion) and water quality
factors including pH, salt and sodium hazards, and toxic ions. The granular and liquid fertilizers
used in fertigation are available in various chemical formulations, solubility and different types of
coatings; therefore selection of fertilizer is an important issue in fertigation Programme. The
selection of granular fertilizer will depend on the nutrient that is applied, fertilizer solubility and
ease of handling.
An essential pre-requisite for the solid fertilizer use in fertigation is its complete dissolution
in the irrigation water. Examples of highly soluble fertilizers appropriate for their use in fertigation
are: ammonium nitrate, potassium chloride, potassium nitrate, urea, ammonium monophosphate
and potassium monophosphate. The solubility of fertilizers depends on the temperature. The
fertilizer solutions stored during the summer form precipitates when the temperatures decrease in
the autumn, due to the diminution of the solubility with low temperatures. Therefore it is
recommended to dilute the solutions stored at the end of the summer. Fertilizer solutions of
smaller degree specially formulated by the manufacturers are used during the winter.
Table 1: Fertilizers solubility and temperatures (g/100 g water) (Wolf et al., 1985).
Temperature KCl K 2 SO 4 KNO 3 NH 4 NO 3 Urea
10°C 31 9 21 158 84
20°C 34 11 31 195 105
30°C 37 13 46 242 133
To ensure the fertilizers selected will not precipitate in irrigation pipe, mix the fertilizer
solution with sample of irrigation water in the same proportions as and when they are mixed in the
irrigation system. If the chemical stays in the solution, then the product is safe to use under
fertigation. Liquid fertilizers offer many intrinsic advantages over granular fertilizers for fertigation.
It is considered as most suitable for of fertigation under micro and sprinkler irrigation. These are
available as fertilizers solutions and suspension, both of which may contain single or multi nutrient
materials.
To avoid damage to the plant roots high fertilizer concentrations, the fertilizer concentration
in irrigation water should not exceed 5%. Although, the susceptibility to root burning from
concentrated fertilizers varies with crops, fertilizers and accompanying irrigation practices,
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