New nitrogen advice has recently been published in
the Teagasc `Green Book' (Major and Micro Nutrient
Advice for Productive Agricultural Crops), writes
Mark Plunkett, soil and plant nutrition specialist,
Teagasc, Johnstown Castle, Wexford
Nitrogen (N) is the key driver of grain yield in cereal production
and is akin to diesel fuel to a tractor engine. Fuel consumption
is more easily measured in a diesel engine and, once you service
your tractor on a regular basis, diesel fuel is used very efficiently.
On the other hand, it can be quite difficult to accurately determine
crops' optimum N for yield at the start of the growing season due
to such factors as soil N release, soil fertility (pH, phosphorus
[P] and potassium [K]), weather conditions (wet/dry) at time of
application and subsequent crop N uptake.
N rates for cereals are based on supplying the difference between
total crop N requirements and the soil N supply. It can be quite
difficult to determine the soil N supply, and such factors as
previous cropping/over-winter rainfall will influence how much
N is supplied from soil reserves. Rainfall levels for January in
many areas are above normal levels so adjustments to final N
applications may be required for 2018 crops. The soil N index
system is used to give an indication of soil N supply (see Table 1).
For example, on a continuous cereal rotation the soil N supply is N
index 1, which reflects a very low soil N supply. Where break crop
such as beans/peas/oilseeds/beet etc. is included in the rotation,
the soil N index is classed as soil N index 2, which indicates that
the soil supplies a proportion of the crop's N requirements during
the growing season.
Table 1: Soil N index for tillage crops.
Soil N Index
Beet, potatoes, kale, oilseed rape,
pea, beans, short-term leys
Swedes grazed in situ
Taking the soil N index in account is the first step to determining
the crop's N requirement in conjunction with crop type and yield
potential. This reduces the risk of under or over N supply, which
can reduce both yield and quality.
I will outline and discuss new N advice for the following crops:
winter wheat, winter barley, winter oats and spring feed barley.
Winter wheat has a large N demand due to its high yield potential,
and N rates should be adjusted based on previous crop yield. Table
2 shows recommended N rates for winter wheat at a base yield of
NEW NITROGEN ADVICE FOR CEREAL CROPS
The main function of the first split of N in winter
cereals (especially barley) is to maintain and
encourage tiller production.
Giving life to your crops
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IFI 200x283.indd 1