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.
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).
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.
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).
Calcium ammonium nitrate, three applications at the beginning of vegetation, GS 30/31 and GS 39/49
Stabilised urea, two applications at the beginning of vegetation and GS 30/31
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.
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.
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.