Field Research & Agronomy

Nitrogen Response and in-season nitrogen decision tools.

Following a pea crop.

This trial was established to investigate the response of wheat to nitrogen (N) application after peas and develop a local N response curve.
Whilst also looking at the value of using N-rich strips and plant tissue testing as decision tools to guide in-season N application.

For full details of this trial contact your local Area Manager, or our Field Research team on research@summitfertz.com.au

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Table 1: Soil Analysis Results

The harvest data showed that there was a statically significant yield response to applied N and there was also a significant difference between replicates.
The highest yield was 5.73t/ha which received the 50% recommendation from the N-gauge treatment at 28kg/ha of N.

The nil N treatment had the lowest yield with 4.35t/ha. On average a yield increase of up to 32% can be achieved by apply N at this site and under this seasons conditions.
The grain quality analysis showed high protein and hectolitre weights, with low screenings.
All treatments had screenings below 5% and hectolitre weights above 74kg/hl and it was protein percentage that determine grading.
Over half had protein percentages exceeding 13% and being graded as H1.
Additionally, there was a trend of increasing protein percentage with increasing application of N.

The N-calculator over predicted the optimal rate for optimising yield and gross margins.
The N-calc application of 20L/ha of UAN as recommended by the in-season nitrogen calculator produced 5.58t/ha yield, whereas the predicted yield was 2.81t/ha.
Increasing the application rate by 50% achieved a decrease in yield by and a 50% decrease of the recommended rate produced an increase in yield.
The protein percentage recommendation was also under predicted.
However, N-calc recommendations did fall at or near the inflection point of the standard N rate response curve indicating that rate recommendations were very close to optimal for yield production.
The N response curves shows a yield benefit to applying N up to around 30kg/ha.

• Scepter wheat had a significant yield response to applied N. The highest recorded yield was 5.73t/ha which received 28kg/ha of N, however the yield response curve showed yield plateauing out at 40N. Grain protein content was high (11.3% - 14.4%) and tended to increase with applied N.
• Tissue testing is a very robust method for making in-season N decision but only shows if a crop is deficient. There is no process for gaining a specific top up application rate to counter act this deficiency.
• The N rich strip is a more reliable and accurate process. The N rate recommendations given did fall close to the inflection point on the N response curve. However, the N-calculator did over predict yield, under predicted protein and it was the 50% of the recommended rate treatment that did optimise yield and gross margins.
• Gross margin calculations had the greatest profit at $1444/ha from applying 28N or 50% of the recommended N-calculator rate. By selecting the most appropriate rate of N an additional $398/ha could be made.
• This trial yielded very high, the 0N treatment on average still went 4.35t/ha. Soil analysis showed that Nitrate (NO3-) level were high in the top 10cm. The recommended rate for applying N after peas under these conditions is 40kg/ha.