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06.09.2019 - Peer Leithold (Send email to Peer Leithold)

Site specific application of growth regulators

Over the past twenty years, state authorities and industrial companies have carried out various precision tests on the use of growth regulators. The research groups came to results, some of which differed enormously from each other. However, some facts can be summarised:

  • All applications of growth regulators reduce the growth heights, early applications to EC 31/32 shorten the lower internodes, the late applications the upper internodes..
  • A high lodging pressure causes lodging in the zero-N
    • By using the growth regulator, lodging extend can usually be reduced. However, this reduction is not always complete.
    • The earlier lodging occur, the higher the yield loss, the later, the lower. Particularly in the case of the prevention of early lodging, the costs of use are recouped solely through the yield advantage. Adjusted for the growth regulators, this yield effect is usually between 50 and 100 €/ha per year. Together with the better harvestability and higher quality of the grain, these measures are highly economical.
  • Low lodging pressure prevents lodging in zero-N
    • The yields of the treated parcels are then (with a few exceptions) usually lower than in the zero parcel.
    • This negative yield effect, supplemented by the costs of the annual growth regulator, also lies between 50 and 100 €/ha.

By deciding on the use of a growth regulator and its correct dosage, the user decides on average on an annual profit difference in the range from 100 to 200 €/ha in grain production. This knowledge alone should motivate every farm manager to find methods and tools that can assess the so-called "storage pressure" as precisely as possible. This is the only way to derive an appropriate dosage of the growth regulator.

Which factors influence use and quantity

The use of growth regulators is primarily dependent on the so-called susceptibility to storage. In turn, the susceptibility to warehousing consists of two components:

  • First of all, the influence of the variety should be mentioned here. Varieties have different stability (see descriptive list of varieties).
  • Secondly, the susceptibility to lodging depends on the growth conditions and the amount of nitrogen available. Looking back, both factors can be seen from the development of populations. In the field, this is done by subjective assessment of crop density, intensity of green colouring and general growth rate.

Looking forward, neither the total nitrogen supply resulting from mineral fertilization and nitrogen release from the soil can be predicted with sufficient accuracy, nor can future weather and growth conditions be predicted. The weather conditions on the day of application determine the intensity of the effectiveness of the growth regulator on the shortening effect of the plant. This means that the use of the growth regulator and its intensity are only possible on the basis of an assessment of the actual situation on the day of application, supplemented by a weather forecast for the next seven days.

Why partial-area specific

The influence of the variety on the lodging risk is known with the limitations already mentioned. The weather, i.e. radiation intensity and temperature, are also known on the day of application. A forecast of the future growth conditions is and remains a forecast with an accuracy of 50 %.

What can be significantly improved when deciding on the dosage of the growth regulator is the measurement of population development and its influence on the expected lodging risk. Good farmers have been dosing higher and higher in high biomass, vigorous crops and reducing in underdeveloped, poorly nourished grain. This subjective assessment of the degree of grain development can be measured precisely and objectively with the N-Sensor® and thus also automated.

This connection will be explained using an example: The picture next to Table 1 shows a lane in a winter wheat field about 250 m long. This was done with a field sprayer equipped with four N-Sensor® heads. The measured nitrogen uptake in kg N/ha is shown here. In addition, biomass cuts were carried out at selected locations. This makes the heterogeneity in the field more than clearly visible.

Table 1 shows exemplarily for the three situations which application quantities are carried out in litres of active ingredient per kg of fresh mass, related to a uniform application in reality. If, for example, the manufacturer's recommendation is to apply one litre of a growth regulator per hectare, then in the less developed areas of the field up to 400 %, based on active ingredient per kg fresh mass, only just under 70 % are applied in the most developed areas. Once again for clarification: it is over-concentrated four times! Physiological stress, extreme cutbacks, growth stagnancy and loss of yield are the logical results.

In the field, the quantities are then usually - and often not so unjustifiably - reduced to 70 % of the manufacturer's recommendation. In the example, the overdosage is then reduced from 400 % to 280 %. The other side of the coin with constant application, however, is that in the highly developed populations, only just under 50 % is then applied. This again opens the door to lodging.

The only way to escape the dilemma is to constantly readjust the quantities by hand when spraying. From a purely statistical point of view, you would have to make about 25 variations per hectare in this case. With 100 hectares of grain, that would already be 2,500 variations. The human eye is not in a position to assess these crop differences continuously and objectively. Our brain would also fail if it were to perform the necessary arithmetic operations reliably and permanently. The figure shows that this heterogeneity can not only be reduced to an arbitrary lane, but that the entire operating area shows these differences. With an N-Sensor® this process can be completely automated.

Agronomic control algorithms

The measured absolute N-uptake is the basis for the agronomic control functions. Absolute measured values and control functions prevent the spraying technology from being over- or understeered. An overdrive causes such a high degree of variation that an excessive reduction in the spray rate on weak parts of the surface can no longer guarantee a sufficient fungicidal effect - the risk of resistance increases. With understeering, on the other hand, the full potential of a variation is not exploited. Only validated control curves ensure the optimal distribution in the area. Long-term tests have shown that this is correct not only from a plant cultivation point of view but also from an economic point of view.

Sensor-controlled application

The procedure of site-specific and sensor-supported application of growth regulators is relatively simple: an expert module proposes a basic dosage based on the variety, the current weather conditions and the long-term assessment (rather dry location/sufficient precipitation). This basic dosage is based on the theoretical maximum nitrogen uptake of a given fruit species and a given EC stage. A maximum dosage is recommended here so that the greatest lodging risk is reliably combated. This can be confirmed or corrected by the user. The sensor then continuously adapts to the currently measured nitrogen uptake during the passage.

Different but absolutely calibrated control functions are available for each culture, application time and active ingredient group. These control functions adjust the basic dosage to the different population situations depending on the situation. Populations with high nitrogen uptake, i.e. high biomass and high nitrogen supply, receive a high dosage. The maximum permissible spray rate is not exceeded. In weak stands, on the other hand, the application rate is reduced. If the growth regulator is applied solo, the application rate is also reduced to zero at a certain point. With tank mixes, however, the system remains at a certain minimum quantity, which must absolutely be applied due to the mixing partner. This is also suggested by the system, but can be corrected by the user.

Test result from six years of field work

From 2008 to 2014, a series of experiments was carried out on 36 large areas for the sensor-controlled application of growth regulators. The available sprayer technology with an N-Sensor® was used in each case. The well-known On-Farm-Research-(OFR-)test design was applied for site-specific questions of Agricon. At least three, usually four or more long plots, consisting of two tramlines, were randomly arranged. All other agrotechnical cultivation measures were carried out uniformly. The plant manager specified the growth regulator quantity of the constant plots.


As described above, the sensor variants were managed with the N-Sensor® system. Although Agricon wanted the nitrogen fertilization to be constantly aligned, in the majority of the trials nitrogen was fertilized with the aid of sensors. The field was uniformly harvested over the entire area with yield mapping. The digital consolidation and linking of the data took place in GIS.

The message reads,

lodging was effectively prevented in all tests (Tab. 2). In the final year there was one exception with a small but not profitable population. This means that the main objective, namely lodging avoidance, was achieved - despite a 12% reduction in total expenditure. As is well known, these were significantly lower on the weak plots. Earnings rose by around 3 %. This is all the more remarkable as most of the nitrogen was applied with the aid of sensors. It can be assumed that the effect in fields that are not sensor-fertilized is once again significantly bigger.

The evaluation of the results of the individual trials with the respective product prices for the growth regulator and the grain resulted in an average economic advantage of € 45 per hectare. The main economic effect is primarily due to the higher yields. As an additional side effect, the farm managers mentioned the relief for the drivers and the generally better distribution of the spray agent.


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