When to apply fertilisers to plants - Soil Essentials: Managing Your Farm's Primary Asset - page 94

• From the soil test, work out which nutrients are needed to raise levels in the
soil to an acceptable range for the crop or pasture in question.
• Apply the fertiliser according to the plants' needs, and to best effect by correct
timing and using the most appropriate application method. For example,
phosphorus can be rapidly tied up in the soil so ideally it should be applied
when the plants need it most and are able to access it. This may mean split
applications in an ideal situation. Potassium is readily leached, and if applied at
heavy rates in one application, plants will take up more than they really need,
and any excess may be lost by leaching.
• Remember, the nutrient present in the soil in the lowest amount relative to
plant needs will limit plant growth. If this is the case, money spent on other
fertilisers will be wasted as the plants are unable to make full use of them. To
maximise the benefit of applied fertilisers, some fertilisers may be best applied
in split applications. This can be achieved by using foliar fertilisers, which are
sprayed directly onto the plants leaves and are rapidly absorbed. As there are
no soil losses with this method of application, less fertiliser is needed.
Alternatively, granular fertilisers can be applied in split applications, but
wastage must be expected, as losses may occur before the fertiliser is absorbed
by the plant roots.
How to apply split applications
Foliar fertilisers
Boom spray onto short crops or pastures.
Apply with a mister to taller crops or pastures.
Apply by aircraft.
Apply to spray-irrigated crops in the irrigation water.
Granular fertilisers
Apply with a fertiliser spreader.
Apply by aircraft.
Timing of applications
The following tables list the best times to apply fertilisers.
Depending on farm resources, the timing of applications may involve
compromising the ideal timing due to practical realities.