Forage Maize Fertiliser Requirements | print version (pdf 196kb) |
Phosphate requirement
The target index for soil phosphorus is Index 2 (16-25 mg P/litre). Large amounts of P are often applied with slurry and consequently fertiliser P applications should be adjusted to allow for this input. Maize removes around 1.4 kg of P2O5 per tonne of silage and this amount should be replaced to maintain the soil P Index at about 2. At lower levels of fertility additional quantities of phosphate are required to improve soil P status whilst with higher fertility there are opportunities for savings. In fact it is important that applications of P in fertiliser and manure should be reduced at higher soil P levels and omitted when soil P is unnecessarily high, i.e P index 4 or above.
Maize has a very high demand for nutrients during its early growth and normally appears to benefit from phosphate placed close to the seed as a "starter" dose regardless of soil P level. Placing nitrogen is also usually beneficial and there is an added benefit from N and P placed together. The fertiliser should be placed 5 cm to the side of the seed row at a depth of 4 cm. It should not be combine drilled because of the risk of damage to the developing roots from high 'salt' concentrations in the soil solution.
A starter dose of N and P can be provided by a suitable N:P compound fertiliser. Diammonium phosphate (DAP) 18% N + 46% P2O5 is one such suitable compound but should NOT be used on soils containing free lime as there is a risk that volatilised ammonia gas can damage roots. Triple superphosphate (TSP) 46% P2O5 should be used on used on soils containing free lime.
"Starter" fertiliser for non calcareous soils
| Soil P Index | kg/ha | kg/ha nutrient | |
|---|---|---|---|
| DAP | N | P2O5 | |
| 0,1 | 185 | 33 | 85 |
| 2 | 130 | 23 | 60 |
| 3 | 45 | 8 | 20 |
| 4 or higher | 0 | 0 | 0 |
"Starter" fertiliser for calcareous soils containing free lime
| Soil P Index | kg/ha | kg/ha nutrient | |
|---|---|---|---|
| TSP | N | P2O5 | |
| 0,1 | 185 | 0 | 85 |
| 2 | 130 | 0 | 60 |
| 3 | 45 | 0 | 20 |
| 4 or higher | 0 | 0 | 0 |
Phosphate recommendations
If a starter application is not made, that phosphate should be included with the main dressing.
Soil P Index |
Starter application P2O5 kg/ha |
Main Application P2O5 kg/ha |
||
|---|---|---|---|---|
| Restricted yield | Average yield | High yield | ||
| 0 | 85 | 10 | 25 | 40 |
| 1 | 85 | 0 | 0 | 15 |
| 2 | 60 | 0 | 0 | 15 |
| 3 | 20 | 0 | 0 | 0 |
| 4 & above | 0 | 0 | 0 | 0 |
Total nitrogen requirement
The average maize crop removes 160 kg/ha of nitrogen. The nitrogen taken up by the crop is made up of nitrogen from the soil reserves and nitrogen from the fertiliser and manure applied. The amount available from the soil is termed the 'Soil N Supply' and this should be used as the basis for manure and fertiliser use. Because maize is very efficient at extracting nitrogen from the soil, experiments in the UK have rarely shown the need apply more than 100 kg N/ha as fertiliser.
It is important to estimate the fertiliser nitrogen requirement as closely as possible. Too little will reduce yield and quality, too much will delay maturity and increase the risk of lodging. An estimate of nitrogen supply is available from the Maize Growers Association from their web site given at the end of this leaflet.
