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 Nitrogen timing


Nitrogen has a vast role to play within plants, it is a part of the chlorophyll molecule and therefore necessary for chlorophyll synthesis, which in turn is required in photosynthesis. A process where the plant uses the sunlight and carbohydrates to produce the energy required for all essential functions such as growth and nutrient uptake. Furthermore as nitrogen is an essential part of the production of amino acids which form proteins, therefore nitrogen is accountable for the quality of the end product, which in majority of our systems is grain protein.

Nitrogen is often taken up by the plant in the  form of nitrate (NO-3) and/ or ammonium (NH+4), retained stubbles and organic matter contain nitrogen  however it must first be broken down by microbes and fungi into a form readily accessible by the plant, this will use other nutrients such as carbon (BCG).

Without adequate and timely nitrogen application the plant cannot synthase enough chlorophyll molecules to maintain healthy plant development. Crop struggling to obtain nitrogen either from the soil or fertiliser can often be stunted, spindly stems, pale green leaves with yellow tips; however the younger leaves will remain healthy due to the mobility of nitrogen.

Spreading the application and amount nitrogen is a cost effective way to maximize the yield and quality of the grain. However there are so many limiting factors to consider when applying nitrogen, what form will you use as well as rates and timing. Westech Ag in conjunction with the BCG has completed trials throughout the Wimmera and Mallee in regards to nitrogen application and timing, this work has determined that applying nitrogen at sowing only has a benefit when the soil N reserve is less than 40kg/ha. However in cereals it is advisable to sow with the seed 20kg/ha of nitrogen in a starter fertilizer such as granulock blend to get the crop out if the ground ready for in crop spreading . Furthermore spreading fertilizer throughout the season permits us to assess the seasonal outlook. This allows you to hold off spreading UREA or spraying UAN and dissolved UREA if the weather outlook is unfavorable.

To encourage tiller growth and stimulate larger head development it is best to apply nitrogen at growth stage 25 ( tillering), later application of nitrogen around growth stage 37-39 will potentially have a yield response and will increase the grain protein concentration although this is dependent of a good finish to the season. Later applications of 40kg/ha nitrogen as a foliar spray at growth stage 75 (milky dough) can potentially lift the protein concentration by 0.75-1% (HGCA, 2009), however this application may not be viable as costs might outweigh the benefit of increasing protein be less than one percent. To be successful in applying nitrogen, either granular UREA, UAN or dissolved UREA, a follow up rainfall event is required to incorporate the nitrogen into the soil root zone before it is volatilised to the atmosphere.  

Overall nitrogen fertilization is an important part of crop development, without adequate nitrogen the crop suffers yield and quality. To maximize the yield potential it is imperative that the nitrogen depending on the form (Urea, UAN or dissolved UREA) should be applied at tillering. To improve on quality a late application at flag leaf could increase protein up to 0.7% and yield up to 0.2t/ha. Nitrogen management is important to the cropping system and should be used depending on seasonal conditions if you are unsure consult your Westech AG agronomist.


The influence of nitrogen timing on yield and ear numbers, Birchip Victoria (Southern Farming Systems/Birchip Cropping Group 2007)



Topcrop zaddock cereal growth scale.