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04.10.2019 - Bodo Hanns (Send email to Bodo Hanns)

The autumn scan of grain and rapeseed

The autumn scan of grain and rapeseed

Many farmers have started with the "autumn scan" in October. They use their YARA N-Sensor® to measure the current N uptake of the winter rape. On basis of the data obtained by this method, they can calculate application maps for the first N dosage in the coming spring. This ensures that the crops are optimally fertilized with nitrogen. The "autumn scan" can save an average of 12% nitrogen fertilizer in winter rape and increase yields by up to 5% at the same time. Current results from agricultural experience show that this approach leads to similar positive effects in winter grain.

An "autumn scan"? What's the point?

In autumn one should already think about the fertilization in spring. How is the correct amount of fertiliser in spring determined? How do you react to differently developed stands in a site-specific way?

The previous approach was to determine the first N application on the basis of N minimum studies or balance models. This is done either by laboratories, the state authorities or your consultant. The problem is that only very few Nmin studies are carried out and these do not reflect the real small-scale distribution in the slightest. On the other hand, it has also been understood that the N minimum value and the correct amount of the first N minimum dosage are only very slightly related. Balance models are completely unsuitable. So what should we do?

Ten years ago, agricultural scientists at Kiel University were able to prove that the N uptake of rapeseed in autumn is closely related to the optimal level of the first N dosage. The higher the N uptake in autumn (i.e. the better the crops are developed), the lower the fertilization has to be. The same applies to winter grain.

The N uptake in autumn is even more suitable because it correlates more strongly with the amount of the first N dose than if you were driving online. After winter we often measure the plant stress caused by winter weather. It can be hoarfrost or residual snow in the stand that falsifies the measurements. With today's state of knowledge, the N-photo taken before winter is the best parameter for measuring the first N dosage.

Scanning with the YARA N-Sensor®

The YARA N-Sensor® is used for an "autumn scan". It can be used to determine differences in the N uptake of plant stands in rape, barley, rye, triticale and normally sown wheat.

The sensor system is mounted on the roof of a carrier vehicle. Due to its flexibility, the new generation of the YARA N-Sensor® ALS can also be mounted directly on devices such as pneumatic fertiliser spreaders. During the crossing, the sensor heads then scan the plant population to the left and right of the lane and measure its current N uptake in kg N/ha. Differences of 60-90 kg N uptake/ha in winter rape and 20-40 kg N/ha in winter wheat are not uncommon within one crop. It is rather the normality. We should react to this as early as possible with an adapted amount of fertiliser.

The data determined by the YARA N-Sensor® are automatically sent to agriPORT and stored. Back in the office, you can display field-specific N-Sensor® maps. They are the basis for the corresponding spread charts for the first N dosage in spring. Farmers, crop consultants or other service providers only have to enter the target value for N uptake, the average dead biomass and the minimum or maximum in agriPORT. The system then generates the N distribution maps.

This example of an autumn scan" in rape shows how much the N uptake can vary within a plot. If a general target value of 160 kg/ha, for example, is taken as the basis for the first N intake in rape, the map shows optimal N fertilisation

A constant fertilisation would lead to a clear over- or undersupply of the partial area.

Why you should also scan winter grain in autumn

The described procedure has proved to be very successful in winter rape for years. In winter grain we also recommend this procedure without reservation. The very good practical experience and the results from practical trials show that we can condition the plants very well for spring dryness with a first N dose adapted to the crop.

In our trials we were able to show that winter barley in autumn 2018 showed average N intake differences between 10 and 43 kg N/ha and winter grain between 5 and 23 kg N/ha. These differences accounted for two to three weeks of vegetation in spring 2019. In difficult years, it is crucial to have closed the plant population as far as possible by the beginning of the lap. If we succeed, the stands will grow almost effortlessly due to the spring dryness. The plants shade the soil completely, the temperature in the stand is lower, more dew, less evaporation.

Well developed population effortlessly create this necessary development process. On the contrary weak populations with low N uptake often do not. Here it is absolutely necessary to trigger a strong development and growing stimulus with a strongly emphasized first N dosage. As a rule, this high amount of nitrogen is not used up until the beginning of the sprout. However, the excess nitrogen is then available as a reserve in the soil if the nitrogen fertilizer of the second N application does not dissolve immediately due to spring dryness. By carefully monitoring the crop with the N-tester, this excess quantity is later caught again.

In order not to overrun stands with high N uptake,  they therefore receive less nitrogen, and populations with low N uptake in the autumn are fertilized accordingly. The N uptake can differ from 10 to 40kg/ha, if we consider that, the N fertilization within one plot may vary from 30 up to 100 kg N/ha.


When "autumn scanning" rape and cereals, you should always consider six important points:


  1. When scanning, the plants must still be vegetatively active. This is often the case with cereals until the end of the year. Rapeseed should be scanned between mid-October and the end of November.
  2. The stands must be free from hoarfrost and dew.
  3. Grain should on average have reached at least leaf stage EC 13/14.
  4. If you have not reached the end of the vegetation during scanning, you can easily take further N uptake increases into account in the later calculation of the scatter map.
  5. Passive N-sensors can currently only be used for approx. three hours a day at noon. The overcast sky offers optimal operating conditions.
  6. Active YARA N-Sensors® (ALS) can be used around the clock. The new generation ALS 2 even for dew-covered populations.

bibliographic reference

This text contains content elements from the professional articles "Inventory management of weakly developed partial areas" (by Peer Leithold; Getreidemagazin 1/2015) and "Die neue Rapsdüngung" (by Bodo Hanns; Raps 1/2015). Both articles are available for you to read.





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