Basic agronomic information
The goal of every fertilisation measure should always be to provide the plant stand with an optimal supply of nutrients. It is, however, questionable where precisely this optimum lies. In general, it is true that the cost of the last kilogram of nitrogen fertiliser must still be covered by the increased yield. If the farmer falls short of this optimum, he/she then loses possible yield and the raw protein values are mostly too low. With a high N input the danger of lodging and pressure of disease increase and the protein content increases excessively. In addition, with N fertilisation way over the optimum the yield sinks again.
In an analysis of N increased-rate trials it becomes clear that there is a different optimal yield for each trial area. The related amount of N differs to a greater or lesser extent. Thus, for instance a yield of between 6 and 12 t/ha is obtained with a fertiliser volume of 250 kg N/ha. Vital: these yields were economically correct in the respective year and trial. Conclusion: there is no fixed relationship between the optimal yield and the related volume of nitrogen fertiliser. The planned yield at the beginning of the fertilisation season is not suitable for determining the optimal N fertilisation.
Flexible fertilising strategies
The reasons for the varying fertiliser requirement lies, on the one hand, in the different growth rate of the plants and, on the other hand, on the continuously changing N availability in the soil. The knowledge of each optimal fertiliser volume can first be determined in the course of the vegetation growth.
In order to determine the current N fertilisation requirement farmers can fall back on the analysis procedure and the measurement device that have been used and tried out for several years in practice. Their use offers precise recommendations for the current N requirement during the vegetation period. With a precision of ± 2 to 3 percent, the N-tester can determine the nutrient status of the plants of a sub-area. With field specific N monitoring the farmer is also able to follow precisely the course of the N uptake during the season and thus to determine the optimal moment for a fertiliser application.
From the small parcel to the field
The information from the N-monitoring and the N-tester are, however, only valid for small areas. On a field, there are often enormous differences in the N supply situation of the plants. Depending on soil and weather the N requirement of a crop can vary by up to 120 kg N/ha within the field, for example due to rises and hollows or heterogeneous soil.
The YARA N-Sensor is able to recognise such differences in the stand. For this the farmer calibrates the YARA N-Sensor according to the fertiliser volume recorded by the N-tester. The YARA N-Sensor implements these recommendations in the field using agronomic control functions for the start, shoots, ears and quality applications.
The measurement of the actual N uptake of the plants has proved to be the best method to derive the sub-area specific optimum N requirement. There is a very close relationship between the measured N uptake and the optimum N fertilisation – determination measure R²=0.8. In the recording of the nitrogen level, both the N content of the plants as well as the crop density are taken into account.
The current spectrum of use of the N-Sensor in cereals includes almost all types of cereal.
| Crop type | Number of regulatory functions |
|---|---|
| Winter crops: wheat, barley and rye, triticale | Start-, shoot-, ear-, quality applications |
| Brewing barley, oats | shoot application |
| Maize | 1 control function |
| Potatoes | 1 control function |
| Oil-seed rape | 1st application, 2nd application |