Forage Maize Fertiliser Requirements

Organic manures

Forage maize is a very convenient crop on which to apply manure or slurry in the spring when there are limited opportunities for spreading on grassland. In the past, heavy applications have often been applied to arable land before sowing maize. Such applications may be counter-productive because they can decrease yield and quality. Applications should not exceed 250 kg/ha of total nitrogen to conform with the Code of Good Agricultural Practice and NVZ requirements.

Be careful that regular applications of manure (or fertiliser) do not increase soil P or K levels beyond Index 3. The uncertainty of nutrient provision from manures requires the regular use of soil analysis to monitor the effects on soil fertility - sample every 4-5 years. Where manure is transferred to maize ground away from another crop (e.g. grass silage) adequate nutrient adjustments to fertiliser policy must be made for the other crop.

The available nutrients in manure or slurry can be very variable. The table below, derived from 'Fertiliser Recommendations RB209, 7th edition' and PDA leaflet 'Nutrient Content of Manures' can be used to estimate available nutrient content. More accurate information can be obtained by having the manure or slurry analysed if it is possible to take a representative sample.

Available nutrients for the next crop following spring application

Manure applied before February may only have half the available nitrogen of a spring application.

Timing of fertiliser application

The importance of placed starter N:P fertiliser has already been discussed. Other fertiliser is best worked into the seedbed. Where large quantities of fertiliser potash are required some should be applied the previous autumn so that no more than 100 kg/ha are applied in the seedbed.

Some of the nitrogen application can be delayed for up to 4 weeks after sowing. Applying one third of the nitrogen after crop emergence has given good results in trials and is especially beneficial in wet years.

Any nitrogen applied after the crop is growing should be placed on the soil between the rows using adapters especially made for fertilising maize to avoid scorching the crop.

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