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- Herausgeber: novum publishing
- Kategorie: Gesellschafts- und Liebesromane
- Sprache: Englisch
The winter wheat yield depends on nitrogen fertilization and on the total precipitation in the main yield-forming months of May and June. Nitrogen fertilization and precipitation in excess of the maximum yield lead to yield reductions. Climate change results in yield reductions with lower monetary returns at high temperatures in May/June of more than 15 degrees. The increased CO2 emissions of the last 25 years, as well as breeding progress, have so far led to yield increases of 50% for winter wheat in Germany. The author underpins his explanations and conclusions, which are presented on the basis of several studies, with numerous data and figures for a better understanding.
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Seitenzahl: 132
Veröffentlichungsjahr: 2025
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Dr. Helfried Zschaler
Ex-post and ex-ante estimation of winter wheat yield as a function of nitrogen Fertilisation, precipitation level and temperatures in Germany
Formerly Institute for Impact Assessment in Plant Protection Kleinmachnow
Ex-post and ex-ante estimates of winter wheat yields in dependency on nitrogen fertilizing and precipitation level as well as temperatures in Germany
Summary
Aim: The aim of the article is firstly to provide information on the influence of N fertilization on yield formation as a function of precipitation levels and to document the consequences of over-fertilization on the ecology. Secondly, the influence of temperature on yield formation, the contribution margin and N fertilization is to be demonstrated.
Material and methods: 249 plot trials were carried out from 2012 to 2022 on nitrogen fertilization in winter wheat and throughout Germany, taking into account the regional annual weather conditions (May + June + 1st decade of July precipitation totals and temperatures). In addition to data on N increase from our own trials, data was provided by the chambers of agriculture. Ex-post regression models for yield as a function of N fertilization and precipitation totals were set up. The contribution margin is calculated as a function of yields, N fertilization and precipitation totals.
Results: With a precipitation total of 190 mm in May, June and the first decade of July and an N fertilization of 200 kg N/ha, the maximum yield is 92 dt/ha. With a precipitation total of 140 mm and N fertilization of 175 kg/ha, the maximum yield is 77 dt/ha. With a precipitation total of 90 mm and N fertilization of 160 kg N/ha, the maximum yield reaches 66 dt/ha. N fertilization exceeding the maximum yield leads to significant yield losses in all precipitation ranges.
With a total rainfall of 220 mm and a May/June temperature of 10 degrees, a yield of 114 dt/ha, a contribution margin of 889 €/ha and an N fertilization of 210 kg/ha are achieved.
With a total rainfall of 50 mm and a May/June temperature of 18 degrees, a yield of 45 dt/ha, a contribution margin of -75 €/ha and an N fertilization of 85 kg/ha are achieved.
Conclusion: The maximum yields, N fertilization and cover crops are significantly positively correlated with the rainfall totals in May, June and the first decade of July.
Yields, cover crops and N fertilization have a significant negative correlation with the May/June temperatures.
Keywords
Winter wheat yield; N fertilization; precipitation; temperatures
1 Introduction
Lawrence (2010) showed in a study that wheat is the most important crop for food production worldwide.
With 2.89 million hectares, winter wheat is the crop with the largest cultivation area and the greatest importance for food production in Germany in 2023.
Winter wheat had an annual net fixation of 788 kg CO2/ha in Germany in 2020 and is therefore climate-positive (BROEKER, 2020).
Groundwater nitrate pollution is still too high in some areas.
The nitrogen surplus must not exceed 50 kg/ha. This value is binding for Germany from 2020 (BMUB, 2016).
According to AWATER-ESPER (2019) and TAUBE (2021), 20 % must be deducted when determining fertilizer requirements in order to relieve the groundwater of nitrate in the "red areas" (with more than 50 mg nitrate/l groundwater).
The main aim of the article is to provide information on the influence of N fertilization, precipitation levels on yield formation and the income situation in agricultural practice and to show the consequences of over-fertilization on the ecology. Furthermore, climate change is to be documented.
2 Material and methods
249 plot trials from 2012 to 2022 were carried out with N fertilizers in the federal states described below, taking into account the regional annual weather conditions with bread and A wheat varieties in fully randomized single-factorial block designs, harvested with plot combines, calculated to 86 % dry matter and evaluated with single-factorial regression analyses. The trials with 55 to 75 soil points included narrow crop rotations (mostly 3-year-olds with winter barley, winter oilseed rape or sugar beet). The trial fields were also fertilized with potash and phosphorus according to the nutrient tests and treated with herbicides against weeds, stalk stabilizers and fungicides (against fungal pathogens) according to damage thresholds (control guide values). Data on N increase with 0 to max. 240 kg N per ha (ZSCHALER et al., 2019) was also provided by chambers of agriculture - Saxony, Brandenburg, Lower Saxony, Thuringia and Bavaria (in some cases with several trials per year and on different sites) - and by the variety trial system in Germany.
The precipitation calculated with the freely programmable software SAS (Statistical Analysis System, USA) only showed a positive correlation with the yield for the months of May and June and the first decade of July.
The multiple intercorrelation coefficient of the precipitation in the present experiments from May, June and the first decade in July of all locations was on average 0.85, with an error probability of p < 0.1. In this article, the precipitation from May and June and from the first decade in July was therefore added together.
The classification into the precipitation areas listed below was based on the meteorological data of the test farms and on information from the German Weather Service.
The Atlantic precipitation level of 190 mm has an average rainfall in May, June and the first decade of July.
The average precipitation level includes an average precipitation of 140 mm during this period.
The low precipitation level of 90 mm has an average rainfall in May, June and the first decade of July.
The precipitation levels differ significantly from each other with an error probability of p < 0.05.
Further definitions: The N balance is the N fertilization in kg/ha and Nmin and N-precrop and N-residual organic minus N-withdrawal by the grain and straw (yield times 2.5 with a crude protein content of 14 % in kg/ha). The output in €/ha is the yield in dt/ha times 23 €/dt (top agrar 2023). The contribution margin in €/ha is the output minus the production costs in €/ha.
The yield coefficient is the yield difference (highest - lowest value of the analyses) divided by the temperature difference (highest - lowest value) indicates by how much the yield increases with a temperature reduction of 1 degree.
All mean values of the optimum yields are rounded.
The developmental stages of winter wheat were named after ZADOKS et al. (1974).
3 Ex-post assessment of the test results
3.1 High Atlantic precipitation level
With average precipitation of 190 mm in May, June and the first decade of July, the yield initially increases with increasing N application and a maximum yield of 92 dt/ha is achieved with N fertilization of 220 kg N/ha (Figure 1). The N balance is -10 kg/ha. With a further increase in N fertilization to 240 kg N/ha, the yield decreases significantly compared to the maximum yield with an error probability of p < 0.1 and also leads to groundwater pollution. The N balance surplus with an N fertilization of 240 kg N/ha and an Nminn of 35 kg/ha is + 44 kg/ha. The N-balance surplus leads to higher climate-damaging N2O emissions and climate pollution (FLESSA, 2019).
Figure 1: Yield [dt/ha] as a function of N fertilization [kg/ha] with average precipitation of 190 mm
3.2 Average precipitation level
With 140 mm of precipitation, the yield initially increases with increasing N application and the maximum yield is 77 dt/ha with an N fertilization of 185 kg/ha (Figure 2). The N balance is -4 kg/ha.
With an error probability of p < 0.1, a further increase in N fertilization to 210 kg N/ha and more results in a significant yield depression and groundwater pollution compared to the maximum yield. The N balance with an N fertilization of 210 kg N/ha and an Nminof 35 kg/ha is 52 kg/ha and is thus slightly above the limit value of 50 kg/ha. The N-balance surplus leads to higher climate-damaging N2O emissions and climate pollution (FLESSA, 2019).
Figure 2: Yield [dt/ha] as a function of N fertilization [kg/ha] with average precipitation of 140 mm
3.3 Low precipitation level
With 90 mm of precipitation in May, June and the first decade of July and with frequent pre-summer drought, the yield initially increases with increasing N application and the maximum yield is 66 dt/ha with an N fertilization of 150 kg N/ha (Figure 3). The N balance is +2 kg/ha. Higher N fertilizations, e.g. 200 kg/ha, cannot be converted into a yield with a significant error probability of p < 0.1 compared to maximum yield due to the insufficient precipitation and lead to groundwater pollution. With an N fertilization, e.g. 200 kg/ha and an Nmin of 35 kg/ha, the N balance is + 69 kg/ha and is thus above the limit value of 50 kg/ha. The N-balance surplus leads to higher climate-damaging N2O emissions and climate pollution (FLESSA, 2019).
In addition, a shorter vegetation period (longer dormancy) limits yield formation and also results in earlier harvest dates.
Figure 3: Yield [dt/ha] as a function of N fertilization [kg/ha] with average precipitation of 90 mm
The optimum yields differ significantly from one another at the individual precipitation levels with an error probability of p < 0.05.
3.4 Germany-wide yield as a function of precipitation
The Excel database (ZSCHALER, 2023a) was used to calculate the yield as a function of precipitation (Fig. 4). The maximum yield of 114 dt/ha is achieved with a precipitation of 220 mm. The minimum yield is 45 dt/ha with a low precipitation of 50 mm. "If precipitation exceeds 340 mm as a result of climate change, this leads to significant yield reductions"
Figure 4: Yield as a function of total precipitation
3.5 Ex-post recommendations for agricultural N fertilization practice
The problem is that N fertilization cannot be predicted with certainty at the start of vegetation. This often leads to misjudgements when assessing nitrogen fertilization. Wheat crops usually come out of the winter well nourished and the good nutritional status should be maintained. If there is no rainfall, the plants suffer from a lack of water, which hinders generative development (grain formation) (Schulzke, 2014). The result is a low TKM. All evaluated trials confirm this physiological correlation.
It is generally advisable to adjust the amount of N to the ecological conditions such as the precipitation level or the expected yield.
DETER (2015) found in an evaluation of the different fertilization strategies of the Institute for Plant Nutrition and Environmental Research Hanninghof on twelve locations that with a split N application (3 x) compared to the single application at the beginning of vegetation, the yield increases by 3 % and the N surplus is reduced from 51 kg N/ha with the single application to 21 kg N/ha with a split N application.
The farmer can now also enter the partial N-applications into his online field record via cell phone or tablet and document them in accordance with the Fertilizer Ordinance (SCHULZE-HARLING, 2021).
There are indications from the literature that the use of the common nitrification inhibitor DMPP usually leads to increased yields and lower environmental pollution (Wissenschaftliche Dienste, 2016).
A separate precipitation measuring device is recommended for the assessment of N applications. For forward-looking N- fertilization, it is helpful to use the medium-term regional weather forecast.
If sulphur deficiency symptoms or low values determined using the Smin method occur, applications of sulphur-containing N fertilizers as well as other macro- and micronutrients (e.g. the foliar liquid fertilizer: YaraVita GETREIDE PLUS, which is also effective against drought stress [top agrar, 2021]) are required so that the N fertilization can be effective, especially at high yield levels.
The distribution of N quantities can be carried out according to the following scheme: For the Atlantic precipitation level of the western federal states with precipitation of 190 mm in May, June and in the first decade of July and with an N fertilization of 220 kg N/ha*, this is minus Nmin as a fertilization recommendation:
1. N application: Stage 23: start of main tillering to promote tillering [40 kg N/ha].
2. N-application: Stage 30: start of shoot growth to strengthen shoots [50 kg N/ha], as the highest N uptake takes place here.
3. N application: Stage 39: Flag leaf fully developed to form thousand-grain weight [60 kg N/ha]. The flag leaf accounts for 40 to 70 % of the yield.
4. N application: Stage 49: for protein formation [35 kg N/ha].
According to the new fertilizer ordinance, the current
Nmin
value from the spring measurement, the nitrogen supply from the organic fertilization of previous years, e.g. 12 kg/ha, the nitrogen supply from the previous crop, e.g. 10 kg/ha for winter oilseed rape, must be deducted from the nitrogen requirement value.
3.6 Ex-post and ex-ante contribution margin calculations
The cover amount is the monetary output (yield in dt/ha times 23 €/dt [top agrar 5/2023]) in €/ha minus the production costs (PK) in €/ha.
The PK in €/ha for the precipitation level of 190 mm is € 1625/ha. They include: Costs for tillage, cultivation, seed, fertilization, plant protection, combine harvesting and wages.
Table 1: Precipitation levels, yields, production costs, temperatures and estimates
Precipitation level
[mm May + June+ 1. decade. July]
Yield [dt/ha]
Production costs
[€/ha]
Temperature
In May/June [degrees Celsius]
Estimation
Very high Atlantic, climate change
220
114
1733
10
ex-ante
High Atlantic
190
92
1625
11,5
ex-post
Middle
140
77
1571
13,5
ex-post
Lower
90
66
1394
15
ex-post
Drought
50
45
1027
18
ex-ante
Precipitation level
May+ June+
1. dec.
July [mm]
Yield [dt/ha]
N-fertilizer. [kg/ha]
Performance
[€/ha]
DB
[€/ha]
May/June Temperature
[Degree]
Estimation
Very high Atlantic, climate change
240
114
210
2622
889
10
ex-ante
Atlantic
190
92
185
2116
491
11,5
ex-post
Middle
140
77
154
1771
200
13,5
ex-post
Low
90
66
132
1518
124
15
ex-post
Drought, climate change
50
45
85
1035
-75
18
ex-ante
Table 2: Precipitation levels, yields, practical N fertilization, outputs, contribution margins (DB), temperatures and estimates
3.7 Ex-post and ex-ante estimation of the influence of temperature on yield and contribution margin in winter wheat
3.7.1 Yield
The following values result for the yield in dt/ha in relation to the temperature in degrees Celsius: The yield formation coefficient is 8 dt/ha with a temperature drop of one degree Celsius in the primarily yield-forming months of May and June. The yield formation coefficient is -8 dt/ha with a temperature increase of one degree Celsius.
3.7.2 Contribution margin
The contribution margin corresponds to the output minus the production costs.
The contribution margin coefficient for a temperature reduction of one degree Celsius is 96 €/ha. With a temperature increase of one degree Celsius, it is -96 €/ha.
4 Ex-ante estimates of potential climate change
A) If predominantly low pressure areas in the period from May to the first decade of July lead to heavier rainfall, then the yield can increase to 114 dt/ha, for example, with 210 kg/ha N fertilization. The contribution margin increases from 114 dt/ha to 889 €/ha.
If, due to climate change, the precipitation totals in the yield-generating months of May, June and the first decade of July exceed 340 mm, this will increasingly lead to significant yield reductions.
The current range of varieties is sufficient to ensure production. As more severe infestation with harmful fungi (foot, leaf and ear diseases) is to be expected, the application of fungicides must be increased for susceptible varieties in accordance with the control guidelines. Multiple applications of stalk stabilizers are essential to avoid crop losses due to storage.
B) If predominantly high-pressure areas in May, June and the first decade of July lead to higher temperatures and lower rainfall of 40 mm, the yield is reduced to 45 dt/ha and the contribution margin to -75 €/ha. To minimize the yield risk, the
