Agronomy Advice

Energising cereal crops with well timed foliar phosphate

Cereal crops often struggle due to low phosphorus levels as a result of low phosphate availability in soils, exacerbated by poor or compromised root systems. Giving these crops a quick 'energy boost' from foliar phosphate is the best way to get them started.

Spreader in a cereal crop field spraying liquid fertiliser
Spreader in a cereal crop field spraying liquid fertiliser

During early spring phosphate availability is often low due to cold, wet or waterlogged soils which can be exacerbated by poor or compromised root systems. This early spring growth period in cereal crops is an essential phase during which the foundation for high biomass is established. High biomass is a fundamental prerequisite to achieving high grain yields. This biomass is the result of achieving a good population of main shoots and tillers. The main shoot numbers are determined by the initial seed rate, and then the subsequent germination % and plant survival.

Tiller numbers are affected by the prevailing conditions during the weeks and months between initial emergence and the growth stage GS 29. The tillering phase commences after leaf 3 is fully expanded and generally finishes when the ‘double-ridge’ stage of development is reached (just before GS 30.) This growth stage is typically reached by mid-March. The final number of tillers can therefore be manipulated through the appropriate use of inputs. One such input is crop nutrition.

Phosphate deficiencies will limit early spring growth

Nutrient deficiencies, especially nitrogen and phosphate, will limit early spring growth and development, thus reducing the number of tillers produced. Such a limitation becomes ever more important in years when drilling is severely delayed, or winter conditions (e.g. water logging or severe cold) prevail.

Waterlogging has been shown to reduce tiller production by 40% to 85% (Malik et al, 2001). Not only is the tillering capacity restricted, but also the root size and structure. This poor rooting further exacerbates the potential for poor nutrient uptake, making the plants vulnerable to stress periods as the season progresses.

Poor rooting further exacerbates nutrient uptake

To give the plants the best chance of early spring growth and development it is important to focus on those nutrients that are most likely to be limiting. Considering phosphate, the processes in the soil that determine how much phosphate is in the ‘available pool’, which is the one that the plants draw from as they require it, are temperature-dependent i.e. cold soils reduce soil phosphate availability.

The developing cereal plants grow at these cold temperatures (approx. 5 – 6 °C), thus potentially exhausting this supply. A poor supply of phosphate restricts the conversion of solar energy into the plant's chemical energy (ATP) that is used during photosynthesis to drive new growth and development.

To help overcome this limitation there are actions that can help. Firstly, consider how the root system can be repaired, or improved to enable better access to nutrients that are available. One way of repairing and building a larger root system is to apply some phosphate through the leaves. Research has shown that an application at GS 25 – 29 can significantly increase the root size/area.

Phosphorus deficiency can limit grain filling too

Later in the season phosphorus is important for grain filling due to its role in energy transfer systems, so any ongoing deficiency can limit grain filling and ultimately restrict yields. Using foliar phosphates at the T2 timing in wheat is an efficient way of getting that all-important P into the plant to enable optimum energy transfer during the critical grain-filling period. Having sufficient P available will help ensure efficient grain filling and good grain size.

Foliar application of phosphate gives an ‘energy boost’ to the crop

A foliar application of phosphate gives an ‘energy boost’ to the crop, stimulating the growth of roots and consequently shoots. Not only does this give an immediate benefit by way of recovery/repair, it builds in resilience, enabling the crop to overcome further potential stress points such as drought during the spring and summer months.

Secondly, it is important to consider the soil nutrient supply and how this needs to be managed. Such an injection of growth through the foliar phosphate application will of course create further demands on the soil nutrient supply to satisfy this new growth. There is the potential that the cold wet soils have a very limited pool of available phosphate that will be quickly exhausted. Therefore to ensure the new growth momentum continues, supply some fresh soil-applied phosphate such as a YaraMila grade.

Effect of foliar phosphate on root growth

This combination of a YaraVita foliar phosphate product along with an application of YaraMila soil-applied phosphate will energise the crop for early, rapid spring growth and development to recover and build biomass for an improved grain harvest. Indeed, recent Yara trials have shown wheat yield increases from 0.23 – 0.6 t/ha.

YaraVita Magphos K or YaraVita Crop Boost are recommended for all cereals

An application of foliar phosphate such as YaraVita Magphos K or YaraVita Crop Boost at 5 l/ha during tillering, ideally GS 25-29, will give a much needed 'energy boost' to get crops moving again. This then should be followed up with a solid NPKS fertiliser such as YaraMila Actyva S very soon afterwards so that the crop doesn’t run out of momentum once it's has started. It is also worth considering a second application at GS 37-51 to ensure sufficient phosphorus is available during grain filling.

Read more about YaraVita foliar fertilisers

Latest advice background
Latest advice background
Grow the future | Nitrogen and sulphur Grow the future | Nitrogen and sulphur

Applying nitrogen and sulphur together just makes sense

Combining nitrogen and sulphur together increases nitrogen use efficiency so means more for your money with less wastage

Find out more

Read about improving nutrient efficiency