Speaker
Description
Introduction
In the near future, we will (hopefully) live in a de-carbonised economy and CO2-neutral produced nitrogen (N) fertiliser from green ammonia will likely be standard in conventional agriculture. The use of such sustainable produced mineral N fertiliser products could become an option in organic farming within strictly limited and regulated rates for applications only in early spring. Compliance monitoring is then expected to be available nationwide and publicly accessible from spectral remote sensing data.
Even though, organically managed soils are known for their high fertility and potential to deliver nutrients from mineralisation processes, the synchrony of plant N demand and supply in early spring is rather poor. Cool temperatures during the important yield determining phase between double ridge and terminal spikelet stages cannot ensure a proper N nutrition for maximal sink formation. Hence, a moderate support from rapidly plant available mineral N fertiliser would help to bridge this gap during the start of the vegetation period in spring.
Materials & Methods
To assess the potential for yield increase from moderate N fertilisation in we used a long-term field experiment (established in 1974) from the experimental farm “Hohenschulen” at Kiel University with full-factorial combined N rate variation (0,40, 80, 120 kg N ha) at all three split applications (beginning of spring growth, stem elongation, ear emergence), leading to overall 64 N treatments. This was implemented in a winter oilseed rape – winter wheat – spring oats – winter barley crop rotation with N rate variation only in wheat and barley in an inverse pattern, resulting in the same amount of total N applied on each plot after one rotational cycle (Sieling and Kage 2021, 2022). Additional fungicide treatments were included within subplots and until 2002 a comparison of full fungicides against no fungicides was available to derive effects of only moderate N but no further synthetic plant protection as estimation for conventional versus low external input. The used cultivars shifted over time and reflected breeding progress.
Results
Highest grain yields in low intensity systems (up to 50 kg N) were achieved from only spring applications (Fig 1A). N response functions showed steeper slopes for N applications only in spring compared to only at later splits or at more applications than the first split. Long-term average grain yields under spring-supported moderate N input environments without additional synthetic plant protection were between 4.9 and 5.3 t ha-1. Under typical conventional three split applications of total 210 kg N ha-1 the average yield was 7.1 t ha-1. The yield gap of low-N-input systems to typical conventional high-N-input intensity of 39% could be reduced to 25-30% with N fertilisation of 50 or 25 kg ha-1, respectively (Fig 2b). When considering shifting 1 kg N fertiliser from high-N-input into low-N-input systems, the yield effect would be doubled (10-15 versus 25-30 kg grain yield per kg N input in typical conventional compared to low-N-input with spring N support).
Discussion
Environmental impacts such as nitrate leaching, or N balance surplus are rather small during early spring applications since leaching below the root zone is unlikely as are problems with high post-harvest N-surplus. Gaseous losses are likely to be less pronounced under low N-input intensity due to a non-linear relationship between fertiliser N input and N2O emissions (Shcherbak et al. 2014). Therefore, a shifting of about 25-50 kg mineral N fertiliser from conventional into low-N-input cropping systems would significantly reduce the net environmental burden in terms of GHG emissions., we could observe a clear increase in apparent fertiliser N recovery over time of which a major contribution might be attributed to newer cultivars (Sieling and Kage 2021).
References
Shcherbak I, Millar N, Robertson GP (2014) Global metaanalysis of the nonlinear response of soil nitrous oxide (N 2O) emissions to fertilizer nitrogen. Proc Natl Acad Sci U S A 111:9199–9204.
Sieling K, Kage H (2022) Winter barley grown in a long-term field trial with a large variation in N supply: Grain yield, yield components, protein concentration and their trends. Eur J Agron 136:126505.
Sieling K, Kage H (2021) Apparent fertilizer N recovery and the relationship between grain yield and grain protein concentration of different winter wheat varieties in a long-term field trial. Eur J Agron 124:126246.
| Keywords | organic agriculture; resource use efficiency; climate change; nitrogen; sustainable intensification |
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