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# Variable N fertilization increases yields and saves nitrogen

This spring, for the first time, the amended Fertiliser Enactment will have a particularly large impact on the N fertilization of agricultural holdings. Restrictions due to the fertilizer requirement value sometimes allow less than 100 kg N/ha in wheat or rapeseed. The operational nutrient comparison and its intensification to 50 kg N balance surplus per hectare in the 3-year average becomes a challenge for many farms. Low yields from the previous year with "normal N-fertilizer quantities" at the same time, but still high organic quantities, make many farmers think and break a sweat. Against this background, increasing N-efficiency is now of the utmost importance! In order to achieve this, N fertilizers must be applied as required.

**Positive impacts are scientifically proven**

The effects on yield and N fertiliser application are certainly among the best investigated parameters in precision farming. These experiments are relatively easy to implement with a functioning yield mapping system and proper documentation of the N fertilizer quantities.

The trials carried out by Agricon and its partners between 2001 and 2014 prove the following beneficial effects:

yield increase | N-reduction | N-balance | |
---|---|---|---|

winter wheat | 5% | 6% | 18 kg N/ha |

winter oilseed rape | 5% | 8% | 22 kg N/ha |

*Table 1: Advantage effect of the variable in comparison to the constant N fertilisation. Calculation from 53 trials WW and 17 trials WR.*

Assuming a price of € 18 for wheat and € 0.95 for nitrogen fertilizers, the average additional revenue is € 74 per hectare. In rape, additional revenues of 92 €/ha can be achieved at an assumed price of 35 €/dt..

**Where do these effects come from?**

The advantage of variable N-fertilization is that we work with intelligent and always objective tools. If these are used in combination with basic agronomic rules, the effects almost adjust themselves by themselves. These basic rules are:

- Every year is different. Plant growth, N-supply from the soil, weather conditions etc. almost always differ from the previous year. In this respect, only limited direct conclusions about the N fertilisation of the current year are possible from the experiences of previous years. This becomes more than clear from the examples marked in red in Table 1.
- There is no connection between the yield and the optimum N fertilisation level. With the implementation of average values or planned yields ("My target is 90 dt wheat, for this I need 200 kg N fertiliser) one cannot achieve optimal yields. This can be seen very clearly in Table 2.
- The yield potential and the associated N requirement only arise in the course of vegetation. In this respect, it is not possible to determine the optimum amount of N fertiliser at the beginning of the season.
- Both factors also differ in the different areas of a field. Relief, soil differences, water retention capacity have different effects on plant growth in small areas. Constant fertilisation on a field inevitably leads to over- and undersupply of partial areas.
- With the appropriate tools, you can always orient yourself to the current N requirement of the plants and apply the N fertiliser - in the right quantity - at the right time - at the right optimum location.

*Tabelle 2: Yields and N expenditure in winter wheat at experimental sites in Saxony. Source: LfULG Saxony, supplemented by calculations by Agricon GmbH.*

### The correct amount

Plant analyses have been used for some time now to determine the current N fertiliser requirement of populations. For cereals we use the N-tester. In the case of non-destructive measurement, the measuring device provides concrete fertiliser recommendations for the application of the shoot- and the ear of the crop. This ensures that the optimum fertilisation is achieved to an accuracy of +/- 2-3% every year.

### The right time

From an agronomic point of view, the right time for N fertilisation can be determined with N monitoring. Regular measurements with the N-tester at a marked point in the field provide a very good view of whether a crop needs to be fertilized again, whether previous doses have been taken, whether the mineralization of soil N has started or whether organic N is effective.

### The right location

The heterogeneity of partial areas can then be determined with the YARA N sensor. The system measures the current N uptake of the plant population. With the help of scientifically based control functions, N fertilisation can be variably applied to any type of fruit at any relevant fertilisation date.

Compared to constant fertilisation, this results in a much more flexible fertilisation strategy that is geared to the N requirements of the plants. This can differ from the constant variant in the timing, amount and number of individual applications as well as the total quantity of N fertiliser.

**Fertilize high-yield zones**

The increase in yield through adapted N-fertilisation is achieved in all the different sections. Weaker populations are boosted by increased N-feeding, better developed sub-areas are not overfertilized.

The exception is heavily underdeveloped populations. Instead, N is significantly saved in these areas if N fertilisation is no longer worthwhile because N uptake is measured too low. In the end, this will continue to lead to in part strong fluctuations in yields within a single field. However, the overall level is higher than with constant N fertilisation. High-yield zones continue to be fertilized, while sections with lower yield potential are increased in yield.

**N balance down - N efficiency up**

With higher yields and lower N expenditure at the same time, the N effort decreases and the N efficiency increases by itself. These two factors are certainly not directly depictable in monetary terms, but they play an equally important role.

On the one hand, the amended fertiliser enactment reduces the permitted N balance excess. By restricting the N-fertiliser quantities, every kg of nitrogen should be used as efficiently as possible if economically profitable arable farming is to continue. In the above-mentioned trials, an average of 10% N efficiency gain could be achieved in wheat and 12% in rapeseed.

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