Basic Agronomics
Winter rape is a valuable crop in our rotation, for many farmers perhaps the most valuable. Winter rape provides the highest cover together with the many possibilities for use. Last, but not least, it is an excellent preceding crop for the cereal rich rotations in market crop farms.
For high economic yields, winter rape has to be intensively managed. High performance varieties, suitable soil cultivation, intelligent pest management and optimal fertilisation must be in agreement with each other.
High yields do not, however, automatically mean large amounts of N fertiliser. Winter rape is already in the public eye, since the high N uptake of a crop is only partly removed from the field with the harvest. The result is high N balance excesses. Usually these can no longer be taken up by the following crop in autumn. With the current production system, winter rape thus has a clear weakness in N efficiency.
Fertilisation model
- Beispiel: N-Aufnahme (kg/ha) in Winterraps
It is thus even more important to react to this challenge with an intelligent N fertilisation. It is common practice to determine the amount of fertiliser using the expected yield, corrected with the Nmin and the expected N mineralisation. Increasingly, additions and reductions for the crop development are also included, as seen in the example for Saxony on the left.
As an alternative to this, the N uptake can be determined through harvesting the above-ground biomass, weighing this and multiplying it by a factor. For this, four representative locations were selected in the rape field and one square metre of above-ground biomass was cut (just above the root) and weighed at each location. The dry matter substance and the N content of the plant vary with the development of the crop. Thus a constant factor should not be used to calculate the N-uptake from the fresh biomass.
The amount of N already taken up (kg/ha) by the plant stand can be derived from the fresh matter determined (kg/m²), as shown in the table on the left. The average of the N uptake is then calculated from the results of the four samples. The farmer then has a reliable basis on which he/she can orient the N fertilisation.
Further models for determination of N requirement are the “French Model” or the Rapsschieber from Rapool.
Fertilisation of oil-seed rape with the YARA N-Sensor
Two methods are possible for using the YARA N-Sensor in oil-seed rape:
On the one hand the YARA N-Sensor can be used with a relative calibration. This means that the farmer decides on the level of fertilisation and regulates the differences in the crop with the N-Sensor. In order to do this the farmer must scan a representative driving lane of the crop. The agronomic calculation is used to assign this scanned measurement data to the average amount of N to be applied. With a well-carried out calibration this agrees with the average amount of N applied.
The advantage is: the nitrogen is applied according to the requirements. Weak stands are strengthened, strong stands are not over-fertilised. In this way, farmers can obtain better yields with the same amount of nitrogen. The disadvantage is: possible savings of fertiliser can only be exploited to a limited extent since the amount of N is still not directly targeted at the plants’ requirements.
This is, however, the case with the absolute calibration: a suitable index especially for oil-seed rape was able to be developed using the measurements from the YARA N-Sensor. This measurement value shows a close relationship to the real N uptake (kg N/ha) of winter rape.
Instead of a visual judgement – as for the rapsschieber – or the time-consuming weighing of biomass and estimation of the N uptake, farmers can determine the real N uptake directly and everywhere in the field with high precision using the YARA N-Sensor.
Optimal N fertilisation
The optimum N fertilisation with the YARA N-Sensor is determined from the difference between the currently measured N uptake and the N-target uptake value recorded in the parcel trials.
The N-target uptake values vary according to the EC stage and the average expected yield.
Control function for the YARA N-Sensor
Control functions are available for the first and second N application in winter rape. The control function describes the amount of fertiliser, dependent on the sensor measurement value or that of the N uptake. Oil-seed rape stands with a high sensor measurement value - high N uptake - obtain a low N fertilisation. With low measurement values – low N uptake – the amount of N applied is increased.
A certain maximum fertilisation should not be exceeded. With extremely weak or damaged sub-areas – blemishes, winterkill – the amount of N is reduced again.