Even though maize crops will not be planted until April and May, early preparation will pay dividends. In particular, the starting point for all nutrient planning should be to check the levels of nutrients available in the soil, says GrowHow farm adviser Ross Leadbeater.
“Nutrient levels can vary a lot between fields so it is important to assess any differences,” explains Mr Leadbeater. “If you have not tested soil in the last three years, then you should certainly check the pH, phosphate, potash and magnesium levels.”
Optimum nitrogen applications are vital for producing a high yielding, profitable crop. Under-supply results in a crop will fall short of its potential, whereas over-supply will give you an excessively leafy plant which is slow to ripen – reducing grain production and the overall energy content of the ensiled crop. Also, over-application of this nutrient can increase the likelihood of nitrogen losses to the environment.
“Estimating soil nitrogen supply can be difficult where slurries and manures have been used,” says Mr Leadbeater. “The field history and RB209 provide a good starting point but taking a soil N-Min test will give certainty about how much nitrogen is available and make sure N rates are spot on.”
Maize is also hungry for potash as well as nitrogen. At index 2-, 175kg/ha potash is needed, but an ‘average’ cattle slurry (6 per cent dry matter) applied at 50m3 will not quite supply this so a dressing of K may be needed. However, soils which have been receiving regular manure will probably be at index 2+ and above so no additional K will be required.
Phosphate requirements are smaller than those for N or K; index 2 needs 55 kg P2O5. Slurry nutrients will normally be sufficient, at lower indices, some phosphate fertiliser will be needed on top of the slurry.
“For all fertiliser applications, I favour working everything into the seedbed and then sowing, as this gets the work out of the way and reduces the risk of crop damage,” says Mr Leadbeater.
“The maize will make use of the fertiliser just as well in the seedbed as top-dressed. If you spread after emergence, there is a risk of leaf scorch from fertiliser getting caught between the leaf and stem.”
Mr Leadbeater also reminds growers not to forget about the maize crop’s appetite for sulphur. “So little is now deposited from the atmosphere that many crops will benefit from an application.
“Trials carried out by GrowHow suggest 20-25 kg SO3 improves yield and N uptake, so it is cost-effective to apply a sulphur-containing fertiliser. For example, this could be applied as 160kg/ha of a combined nitrogen sulphur fertiliser such as 27 N + 12 SO3 which would supply 43 kg N + 20kg SO3.”