How should nitrogen fertilisation take place when using conserving soil working techniques? A difficult question because arable land can look very different especially when a plough is not used. Dr. Konrad Steinert, LOP Landwirtschaft ohne Pflug (Agriculture without the Plough), explains the solutions.
If a plough is not used, the very different conditions may lead to completely different fertilisation strategies, as demonstrated by the following examples: even if no ploughs are used, many farmers carry out relatively intensive soil cultivation: disc harrow, tiller and rotary harrow for seeding. The straw is then almost completely decomposed next spring, and there are almost no differences for fertilisation following the plough furrow. This applies particularly after favourable preceding crops, such as rapeseed, potatoes, pulses, or after straw removal.
Even with ploughless tillage, very different conditions may apply after preceding grain crop. The surfaces are ideally structured and aerated in parts, such as in soils with high biological activity or when seeders for strip tillage are used. In this case, it is not uncommon for the stocks to be ahead of seeding after furrow ploughing because ploughed surfaces silt up considerably so that the soil life lacks oxygen and mineralisation sets in later than on unploughed surfaces.
On the other hand, there are also many areas tilled without a plough where the soil is denser meaning it dries late in spring and thus only warms up slowly. Here the vegetation and mineralisation starts late, and the development of these areas lags behind those tilled conventionally. In this case, it is most certainly right to moderately increase the first fertiliser application in order to kick start juvenile growth and tillering; in turn the following fertiliser applications can then be reduced.
Thus, there is no blanket solution for nitrogen fertilisation in case of ploughless soil cultivation. It is too difficult to predict how much nitrogen will be released by mineralisation in the following vegetation process.
Straw as a nitrogen barrier
In case of conserving soil cultivation and especially in case of direct sowing, permanent soil COVER using straw and crop residues are applied as protection against drying-out and erosion. Finally yet importantly, the mulch layer constantly provides the soil life with nutrition, from which anectic earthworms particularly profit. Thus, many non-ploughing cultivators do not aim for rapid removal of the straw, but rather want to retain the straw COVER on the soil surface at least until the end of the successive crop. A long interval crop rotation prevents pathogenic organisms, such as HTR/DTR or Septoria tritici, from surviving on the straw residues and infecting the successive crop.
Potentially, however, the straw on the soil surface may cause a nitrogen blockage. The straw has a very low C:N ratio, and for this reason the micro-organisms living there require nitrogen. This nitrogen comes from the soil reserves as well as from the spread nitrogen fertiliser, and is subsequently immobilised for a certain period in the microbial protein. This effect may be more pronounced by flat straw incorporation into the soil, than if the harvest residues remain in the soil surface completely in case of direct sowing. Given conventional nitrogen fertilisation, it is difficult to judge the degree of fixation.
Alternative for more CONTROL: Fertiliser injection
The supply of nutrients is more controllable if the nitrogen fertiliser is applied directly to the root by injection into the ground. By placing the fertiliser below the straw COVER, interactions between fertiliser and straw are avoided – even under unfavourable meteorological conditions, the plants continue to have access to the urgently required nutrients. At the same time, this method also avoids gaseous nitrogen losses.
As a rule, this fertiliser injection is carried out by using “pin wheels” as CULTAN fertilisation (Controlled Uptake Long-term Ammonium Nutrition). These ammonium deposits are stable in the ground for a longer period of time. The plants tap these deposits with their roots and remove the nitrogen according to their requirements. For this reason, direct sowing and the CULTAN process fit especially well together, and the good nutrient availability during spring drought must be especially emphasised. Apart from spiked wheels, there are other possibilities that can be used for depot fertilisation, such as the use of hose spreaders or slot runners in conjunction with the use of stabilised ammonia fertiliser. In practice, liquid fertilisers are applied also, such as AHL, even if this does not quite meet the requirements of the CULTAN process due to its level of nitrate. As growing crops have a very high nutrient requirement in spring, these “compromise procedures” have also been able to prove themselves.
Positioned fertilisation while sowing
In the meantime, appropriate combined machines with integrated fertilisation for positioned application while sowing are available from almost every manufacturer. For summer grain in particular this process has proved itself very well, where as a rule ammonium-containing N-fertilisers are used in addition to phosphate fertilisers, and sometimes even complete fertilisers. When using root fertilisation, especially for spring barley, the entire N demand can be applied to the seed. Newer machines today combine a surface fertiliser placement (side dressing) with a topsoil placement (subsurface) in order to ensure ideal nutrition for the young plants on the one hand, and also to stimulate the growth of roots at depth on the other hand. Practitioners report that stock sowed by strip tillage survives dry periods better than conventionally fertilised crops, and in the end produce distinctly higher harvests.
In case of winter grain, this process is said to produce strong and deep rooting stocks when using medium and late sowing, the development of which does not require encouragement with an extra portion of fertiliser in spring. However, the new Fertiliser Ordinance brings additional limitations, especially in the case of autumn fertilisation. A sensible possibility here is the application of seed tape fertilisation. Here special fertilisers, which also contain easily available bulk minerals and trace elements and are well tolerated by the plants, can be introduced in solid or liquid form into the seed furrow along with the seed. Less than 10 kg/ha of N is sufficient to effectively boost young plants.
With deep straw incorporation and good preceding crops, the nitrogen fertilisation of grain without the use of a plough does not differ from that under conventional soil working methods. However, the more the cultivation intensity is reduced and the more straw and crop residues remain on the soil surface, then the greater is the need to consider alternative fertilisation procedures. At the same time, greater emphasis on the first fertiliser application to promote weaker crops remains only an emergency measure!
The entire cultivation system should ensure development of the young plants and an ideal nutrient supply to the plants. Optimal tilth is the prerequisite for intensive root penetration and use of the moisture and nutrients in the soil – management measures, such as controlled traffic farming or strip tillage can help to achieve this aim. A CULTAN fertilisation, stabilised fertiliser or fertiliser placed directly with the seed when drill sowing are sensible methods here.
An optimal nutrient supply also increases the stress tolerance of the stock. Higher yields with moderate fertilisation not only improve the economic efficiency of the process for the farmer, but they leave behind less nitrate in soil after harvest to then possibly leach into the ground water.
Status: 17th December 2015