Spring a crucial time for fertiliser P on grass swards

P exists in soil mainly as negatively charged ions dissolved in the soil water. However, these ions are present at very low concentrations because P readily binds to soil particles, especially clays and iron or aluminium oxides. As a result, P moves very slowly in soil and usually reaches roots by diffusion, rather than by mass flow (e.g. nitrogen).

In spring, grass growth resumes rapidly as soil temperatures rise above about 5.5 – 6 °C. P plays a critical role in early root development, tillering, and energy transfer within the plant. When roots absorb P from the surrounding soil solution, a concentration gradient is created, causing more P to diffuse toward the root. The rate of P diffusion is limited in the spring by soil type, low soil temperatures, below optimum soil P indices and low soil pH.

Applying half of your annual P requirement in March and April ensures that readily available P is present when grass plants are actively developing new roots and shoots, supporting early growth and higher spring yield. Trial results demonstrated that P applications in spring in conjunction with nitrogen and sulphur increased spring grass yields by 22 – 29%.

Finally, spring application fits well with grassland management practices for silage and grazing. Using products such as YaraMila ExtraGrass or YaraMila SulphurCut this spring will supply enough early P to support maximum sward growth in the early part of the season.