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18.04.2018 - Bodo Hanns (Send email to Bodo Hanns)

Do we really have to fertilize at maximum?

Since the amended Fertilizer Ordinance (DüV) became effective in summer 2017, farmers are obliged to determine a fertilizer requirement value N for all relevant arable crops and grassland. This is also the maximum permissible N fertilization level.

A major point of criticism of this regulation is that it is largely the same for all farms in Germany, irrespective of location, soil properties and annual weather conditions. In case of doubt, the maximum permissible N fertilization amounts on loamy sand hardly differ from the amounts on a loamy soil site.

With regard to the Fertilizer Ordinance, farmers face the challenge of achieving the best economic result on their farms as a businessman. In plant cultivation, optimum yields must be achieved with simultaneous high efficiency in the use of nutrients.

The owner of a mere fruit farm with short crop rotation may now think that the new regulations will not cause them any major problems. For yield management with mineral fertilizers is relatively easy to manage. However, this is too short-sighted, because in the medium term, soil fertility will suffer from this strategy. Therefore there is a need to take action on these farms.

On the other hand farms using organic materials (animal husbandry, biogas) must already pay attention to the avoidance of damage and to application quantities and dates if they want to achieve the optimum yield in terms of plant nutrition.

Regardless of the type of operation or cultivation, the industry is almost unanimous in its belief that capping the N quantities will have a more or less negative effect on yields. The reason for this is in the still widespread "accounting thinking": For a decitonne yield I need x kg N-fertilizer/ha.

However, this is not entirely correct, as the approach has two major flaws:

1. An expected yield is assumed for the N fertilization: this is usually the average of the farm. However, the exact yield of the current year is not known at the time of fertilization.

2. Total amount of N: this consists of the N fertilizer and the soil N. However, the proportion of nitrogen supplied from the soil cannot be determined on a flat-rate basis, but depends on various parameters which only become apparent in the course of the vegetation period.

The two essential components of the balance model and the determination of N fertilization are strictly speaking, two unknown variables.

What does this mean for fertilization? Depending on how the year, the location or the sub-area develops, these variables turn out very differently. The optimum fertilization level must also be correspondingly differentiated.

This can be illustrated very well using the example of the long-term yield trials of the Free State of Saxony (Fig. 1 on the next page).

Figure 1: Yield trials (nitrogen increase trials in small plot plants) from 1994 to 2013.

year	base yield (dt/ha)	optimal N-expense (kg/ha)	optimum yield (dt/ha)
2013	43,5	216	80,4
2012	50,7	240	106,5
2011	65,7	205	113,6
2010	55,1	202	97,8
2009	54,4	203	102,6
2008	73,5	141	103,6
2007	75,8	166	104,3
2006	69,2	173	83,5
2005	55,8	213	105,5
2004	89	153	105,5
2003	45,9	158	65,2
2002	75,7	81	84,6
2001	64,7	191	87,4
2000	74,5	151	95,7
1999	59,9	159	86,3
1998	81,3	60	85
1997	48,9	194	83,2
1996	66,3	159	95,4
1995	71,4	115	83,4
1994	62,1	133	82,8
minimum	43	60	65
medium	64	166	93
maximum	89	240	113

Source: Saxon State Office for Environment, Agriculture and Geology, Dr. Albert

Three important pieces of information can be derived from these values:

They illustrate how large the fluctuations in yield (optimum yield) can be between the years. The average yield of approx. 90 to 95 dt/ha is hardly affected, but much more often lower or higher yields are achieved.
They clarify how much the optimum N fertilization level can vary between the years.
In addition, the fluctuations in the basic yield show how big the influence of the factors weather, soil and soil N on the yield is.

Considering this intel we can make the following statement: There is no fixed relationship between the yield and the optimum amount of N fertilizer required for it! A yield of 80 to 85 dt/ha can or must be produced with 80 kg N/ha or 150 kg N/ha or also 200 kg N/ha optimum fertilizer.

Therefore, no serious statement can be made as to whether the fertilizer requirement of a fruit species will be limiting this year.

Once again for clarification:

If you take the tests from Saxony as a basis and compare these with a standard fertilizer requirement value according to DüV of 183 kg N fertilizer/ha (WW A 230 kg / yield average 93dt/ha +13 kg / Nmin -50 kg/ha / previous crop effect -10 kg), the following result is theoretically obtained:

Fertilizer requirement value: 183 kg N fertilizer /ha
Fertilizer requirement value for achieving optimum yield exceeded: 8 out of 20 years
Fertilizer requirement value for achieving the optimum yield undershot: 12 out of 20 years

However, these facts can be countered with a flexible and variable N fertilization. With the Agricon N fertilization method, the resource nitrogen can be used highly efficiently in time, quantity and location. With our digital solutions, every farmer can - also under the conditions of the amended Fertilizer Ordinance - operate in an economically and ecologically optimal manner and ensure the future viability of his farm.

Further information on the Agricon N fertilization process: www.agricon.de/n-duengung

This project received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement 720176.