An on combine NIR analyser measures protein, moisture, oil and starch in real time as grains are harvested. By combining protein and yield along with GPS coordinates, a new field map, Protein/Yield Correlation Quadrant Map, is generated that identifies zones where the protein is low, and the yield is low. These zones are where the application of more nitrogen fertiliser will produce a positive yield response.
Water and nitrogen are the two major drivers of yield within cereal crops. Insufficient nitrogen availability and uptake by plants throughout the growing cycle will limit the yield of the crop.
Accurately identifying the zones within a field where yield has been limited by the nitrogen availability, has been the objective of precision agriculture for more than 30 years. Many technologies have been developed to measure the nitrogen content and distribution in soils across the field as well as measuring the effect of water and nitrogen on the biomass production.
These technologies have several limitations in that they do not reliably identify nitrogen limited zones. Now there is a new technology that measures the nitrogen in the seeds in the form of protein. An on combine NIR analyser measures protein, moisture, oil and starch in real time as grains are harvested. By combining protein and yield along with GPS coordinates, a new field map, Protein/Yield Correlation Quadrant Map, is generated that identifies zones where the protein is low, and theyYield is low. These zones are where the application of more nitrogen fertiliser will produce a positive yield response.
This article describes the three technologies that are available for farmers to measure nitrogen in the soil and discusses the application for each technology and the potential benefit offered to farmers.
There are many scientific reports that demonstrate the relationship between nitrogen and yield in cereal crops, i.e., wheat, barley and corn. Nitrogen is required as the seeds sprout and emerge through the soil. If there is not enough nitrogen, then the plant may not develop the full number of tillers which then sets up the yield potential for the crop.
During the stem elongation and leaf development stages, nitrogen is required in photosynthesis to produce the sugars and proteins that eventually make up the plant. Insufficient nitrogen during the biomass production stages will limit the size of the plant and the yield of the fruit that it will produce.
Lastly during the flowering and seed development stages nitrogen is transported from the stem and leaves and used in the development of the final seeds. Insufficient nitrogen may cause the plant to reduce the size and number of heads or cobbs and thus reduce the yield. If there is sufficient nitrogen and water throughout all stage of the plant’s development, then the plant should grow to achieve the full yield potential. If there is excess nitrogen available, then it will result in more protein produced in the seeds.
Measuring nitrogen in the soil, the stems and leave and then in the seeds requires three different technologies.
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By combining protein and yield data collected off the combine harvester a more complete picture of the nitrogen availability and uptake by the plant can be developed. A new map called the Protein/Yield Correlation Quadrant map is generated by correlating the protein and yield across the field. By tagging the GPS coordinates with the protein and yield data, this map identifies four performance zones of where and how much Nitrogen has been used by the crop at various stages of the growth cycle. The plot shows the four zones.
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The zones where the protein is low are where nitrogen has limited the growth of the plant and eventually the seeds. The zones where the protein is high are where there has been sufficient or surplus nitrogen to ensure the full yield potential has been achieved and the protein content optimised.
Research from Australia, UK, Canada and USA shows that for wheat and barley crops, when the protein content of the grains are less than 11.5%, then the crop would have achieved a positive yield response with the addition of more nitrogen fertiliser. By identifying the low protein zones within a field provides a simple and accurate means of generating variable rate nitrogen fertilisation prescriptions that will increase yield and protein across the field.
Case Study: Canadian barley field protein variations
Steve Larocque, Beyond Agriculture, Calgary, Alberta, has used the CropScan 3000H to measure protein in barley. As a leading agronomist, Steve has pointed out that to achieve the correct yield in wheat and barley, then the protein in the seeds should be between 11.5-12.0%. His plot of nitrogen application vs. yield and protein shows that the yield reaches an optimum when the protein is around the 11.5% level.
Steve conducts trials for new fertilisers, insecticides etc. In this field he was trialling an injectable N fertiliser down the middle of the field. The green band down the middle of the Protein Map corresponds to where he applied extra N fertiliser during the flowering and filling stages of the plant development. The map shows that the areas where the Protein Map is Green and Yellow, i.e., > 12%+, correspond to the higher yield areas, Green and Yellow, in the Yield Map. Whereas the low protein areas, Red, of the Protein Map correspond to the low yield areas, Red and Orange, of the Yield Map.
Case Study: Western Australian wheat field response to nitrogen fertiliser
Matt Hill, a farmer from Esperance, WA, conducted strip trials to see how much yield increased with the application of higher rates of Flexi N nitrogen fertiliser. The figure below shows the Protein/Yield Correlation Quadrant Map for a wheat field on his farm. The Red zone that is marked, had previously produced low yield and low protein wheat, and thereby was projected to produce a positive yield response to increased nitrogen fertiliser.
The table shows the Yield and Protein response to increases in the rate of Nitrogen applied across the field. The Yield Vs Nitrogen Application Rate shows that approximately 100 litre of Flexi N fertiliser produces an additional 0.6T/ha and approximately 1% higher protein.
Mr. Hill realised that he had under fertilised this field and the lost yield was approximately 750kg/ha. He estimated that he could increase his revenue by $ 200/ha by increasing the rate of nitrogen fertiliser based on the protein content of the wheat.
50% of wheat fields across Australia under fertilised
According to GRDC data, the average yield of Australian wheat crops is 1.7 t/ha whereas the yield potential should be 3.4t/ha. ABARE data shows that the average protein content of Australian wheat is 9.,5%.
Based on 11.5% protein being the point where the yield is optimised, then approximately 50% of the wheat fields across Australia is under fertilised. By identifying the low protein zones within wheat and barley fields across farms, then the yield has the potential to be increased to 3.2t/ha. This could increase production of wheat and barley in Australia by 25 million per annum tonne with a value of $ 9.3 billion dollars.