Precision FarmingEffects of crop manage­ment on wheat yield and grain quality

A joint field trial by John Deere and Saaten-Union is inves­ti­gating the influ­ence of various para­me­ters such as fertil­iza­tion, seed density and growth regu­la­tors on the yield and protein content of winter wheat.

Crop­ping systems are being chal­lenged by rising input costs and pres­sure on producer prices. The EU public also demand that area-related subsi­dies should be linked to providing so-called public goods. Growers must there­fore continue to opti­mise crop­ping systems to ensure prof­itability. A joint field trial by John Deere and Saaten-Union will inves­ti­gate the influ­ence of various para­me­ters on winter wheat yield and protein content.

The exper­i­ment

Yields and grain quality can be influ­enced by plant protec­tion, fertil­i­sa­tion, variety selec­tion, seed density and the use of growth regu­la­tors. Varying those factors and measuring the impact will show the effects of different manage­ment strate­gies.

Exper­i­mental sites and set-up

The first exper­i­mental site (S1) in Upper Bavaria has parabrown soil while the second site (S2) in the Magde­burger Börde has rich black soil. S1 is char­ac­terised by higher annual precip­i­ta­tion totals (about 850mm) and usually balanced precip­i­ta­tion distri­b­u­tion. S2, on the other hand, is located in the rainy half­shade of the Harz Moun­tains, so the average annual precip­i­ta­tion is higher, albeit with a pronounced early summer drought.

The strip trials were created with two (S1) and four (S2) repe­ti­tions. At Site two, three indi­vidual samples were harvested from each plot using a plot harvester (=864 measure­ments). At site one, each plot yielded four indi­vidual samples (=288 measure­ments).

Mean grain yield and protein contents as a func­tion of seed density and form of nitrogen fertiliser.


Two modern winter wheat vari­eties were sown at seed rates of 80, 160 and 240 grains/m² (at S1)and 100, 160, 220 and 280 grains/m² (at S2). The aim was to confirm the poten­tial for reducing seed rates compared to the usual prac­tice. As a basis for the entire exper­i­ment, an optimal seed place­ment in the soil was realised by using a modi­fied drilling tech­nique.

Düngung Fertil­i­sa­tion

Half of the plots received a rapidly avail­able ammo­nium nitrate fertiliser (N) in the form of calcium ammo­nium nitrate divided into three appli­ca­tions according to crop need. The other plots received a slow-acting urea fertiliser in only two early appli­ca­tions, both of which saved a pass and took into account the increasing aridity in early summer. The trials simu­lated a 20% reduc­tion in all N appli­ca­tions to simu­late the effects of regu­la­tions in water protec­tion areas, according to which the total fertiliser calcu­la­tion was made on a site-specific basis (Nmin early in the year S1: 60 kg/ha, S2: 45 kg/ha).

N-Strategy 1:

Calcium ammo­nium nitrate, three appli­ca­tions at the begin­ning of vege­ta­tion, GS 30/31 and GS 39/49

N-Strategy 2:

Stabilised urea, two appli­ca­tions at the begin­ning of vege­ta­tion and GS 30/31

Growth regu­la­tors

Growth regu­lator strategy 1

for stalk stabil­i­sa­tion: 0.4 litres/ha product with trinexapac-ethyl at GS 31/32

Growth regu­lator strategy 2

for stalk stabil­i­sa­tion and simul­ta­neous breaking of apical domi­nance: Two appli­ca­tions of 0.5 kg/ha product with prohexa­dione calcium and trinexapac-ethyl at GS 20/25 and 37/39

Growth regu­lator strategy 3

for stalk stabil­i­sa­tion, short­ening and calcu­la­tion of apical domi­nance: 0.8 litres/ha chlorme­quat-chlo­ride at GS 25/30 and 0.3 litres product with trinexapac-ethyl at GS 31/32


The two exper­i­mental sites differed signif­i­cantly in yield across all exper­i­mental vari­ants. S1, with an average grain yield of 10.1t/ha, was a good 2t/ha below the average yield of S2 (12.3t/ha). These high yields were achieved despite the spring drought in the Magde­burger Börde region and the unusual heat and drought in the grain filling and ripening phase in Upper Bavaria. In Magde­burger Börde (S2) there was low rain­fall, but it rained at the right time.

Effect of growth regu­la­tors by seed density (CMC: chlorme­quat chlo­ride, Trinex: trinexapac-ethyl, TrinPro: trinexapac-ethyl and prohexa­dione calcium).

Influ­ence of fertiliser on yield and crude protein content  

The impact of different fertiliser regimes was evident at both sites. The urea produced higher yields except at the lowest seed rates (Figs. 1 and 2) at the Bavaria site. Overall, the protein contents were very low, below 11.5%, and only reached feed wheat quality.

In contrast, calcium ammo­nium nitrate at the Börde site produced yields that were. 0.65t/ha higher than where urea was used. These plots all achieved nearly 13t/ha or more – even at the lowest seed rates. Despite the high yield, protein contents aver­aged above 12%. All urea vari­ants achieved A-quality grain with over 13% protein content. This may be due to the fertiliser form, which had a posi­tive effect on protein synthesis due to a later avail­ability of the stabilised urea. Or the dilu­tion effect in the lime ammo­nium nitrate trials may have resulted in lower protein levels due to higher yields.

Growth regu­lator strategy

At low seed rates, the target yield can only be achieved with good tillering. At the same time, apical domi­nance of the main shoot coun­ter­acts high yield and crop even­ness. The aim was to break the apical domi­nance of the main shoots or to achieve stalk stabil­i­sa­tion, espe­cially at low seed rates, by means of suit­able growth regu­lator strate­gies. The vari­ants with chlorme­quat chlo­ride and a product containing trinexa-pac-ethyl produced the highest yields among medium seed rates.

However, with only 80 grains/m² at S1, the effect of too low a seed rate was greater than the benefit from breaking apical domi­nance. At S2, the effects were even more visible. Here the CMC+ Trinex site achieved a yield advan­tage of 0.2 and 0.4t/ha at the medium to low seed rates of 160 and at 100 grains/m², respec­tively (figs. 3 and 4). The trial with only one dose of trinexapac-ethyl at GS 31/32 and a seed rate of 220 grains/m² showed posi­tive yield effects at S2. In contrast, at S1, applying the product twice with trinexapac-ethyl and prohexa­dione-calcium showed addi­tional yields of just over 0.3t/ha at a seed rate of 240 grains/m².

View into the wheat field
Wheat popu­la­tion at reduced seed rate

N balance

It is note­worthy to look at the N balance after the exper­i­ments were conducted at both sites. S1, including the Nmin values, has an almost balanced N record (calcu­lated as an average of +0.4 kg N/ha for all plots). Here, under the premise that Nmin values remain constant on average, a balance of the soil N can be expected.

However, a consid­er­a­tion of the N balance without including the highly volatile Nmin value from the spring would show a clearly nega­tive balance between fertil­i­sa­tion and crop use for S1. In contrast, the blow on S2 has a calcu­lated mean of -106.2 kg/ha across all plots. The high protein contents combined with high grain yields, which are usually not expected, meant more N removal versus inputs. However, looking back over the past few years, S2 shows high volatility in returns: In years with low yields, N balance can be achieved with fertiliser appli­ca­tions based on fertiliser regu­la­tions, but even with average to high yields, sticking to the regu­lated amount results in a clearly nega­tive N balance.

This is likely to result in humus deple­tion as well as the asso­ci­ated nega­tive effects on soil fertility and the envi­ron­ment.


The effects of seed rates and the two forms of fertiliser were signif­i­cant this year once again. The results showed that seed rates can be reduced in winter wheat compared to those used in common prac­tice. Modern wheat vari­eties are very adapt­able to the avail­able stand space and achieve high yields and grain quality even at reduced seed rates.

Using a readily avail­able N fertiliser (in this case, calcium ammo­nium nitrate), which promotes strong plant growth, in combi­na­tion with a growth regu­lator strategy that prevents excess biomass from being formed, can increase winter wheat yield. However, this often corre­lates nega­tively with crude protein levels. Higher protein levels are more likely to be achieved with stabilised urea. Depending on the target market, this can be econom­i­cally advan­ta­geous because a third pass for fertil­i­sa­tion is prevented and this, together with the quality premium, can compen­sate for lower yields.

Peren­nial high N-removal, as observed at the site in the Magde­burger Börde, cannot be compen­sated for within fertiliser regu­la­tions. In the medium term, this will lead to a decrease in soil N stocks and there­fore to humus deple­tion. A 20% reduc­tion of N fertiliser against the calcu­lated N-require­ment, as carried out at both trial loca­tions with regard to the “red areas”, is there­fore to be seen very crit­i­cally with regard to the medium and long-term agro­nomic and ecolog­ical effect.